JavaTM 2 Platform
Std. Ed. v1.4.2

java.lang
Class String

java.lang.Object
  extended byjava.lang.String
All Implemented Interfaces:
CharSequence, Comparable, Serializable

public final class String
extends Object
implements Serializable, Comparable, CharSequence

The String class represents character strings. All string literals in Java programs, such as "abc", are implemented as instances of this class.

Strings are constant; their values cannot be changed after they are created. String buffers support mutable strings. Because String objects are immutable they can be shared. For example:

     String str = "abc";
 

is equivalent to:

     char data[] = {'a', 'b', 'c'};
     String str = new String(data);
 

Here are some more examples of how strings can be used:

     System.out.println("abc");
     String cde = "cde";
     System.out.println("abc" + cde);
     String c = "abc".substring(2,3);
     String d = cde.substring(1, 2);
 

The class String includes methods for examining individual characters of the sequence, for comparing strings, for searching strings, for extracting substrings, and for creating a copy of a string with all characters translated to uppercase or to lowercase. Case mapping relies heavily on the information provided by the Unicode Consortium's Unicode 3.0 specification. The specification's UnicodeData.txt and SpecialCasing.txt files are used extensively to provide case mapping.

The Java language provides special support for the string concatenation operator ( + ), and for conversion of other objects to strings. String concatenation is implemented through the StringBuffer class and its append method. String conversions are implemented through the method toString, defined by Object and inherited by all classes in Java. For additional information on string concatenation and conversion, see Gosling, Joy, and Steele, The Java Language Specification.

Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.

Since:
JDK1.0
See Also:
Object.toString(), StringBuffer, StringBuffer.append(boolean), StringBuffer.append(char), StringBuffer.append(char[]), StringBuffer.append(char[], int, int), StringBuffer.append(double), StringBuffer.append(float), StringBuffer.append(int), StringBuffer.append(long), StringBuffer.append(java.lang.Object), StringBuffer.append(java.lang.String), Charset, Serialized Form

Field Summary
static Comparator CASE_INSENSITIVE_ORDER
          A Comparator that orders String objects as by compareToIgnoreCase.
 
Constructor Summary
String()
          Initializes a newly created String object so that it represents an empty character sequence.
String(byte[] bytes)
          Constructs a new String by decoding the specified array of bytes using the platform's default charset.
String(byte[] ascii, int hibyte)
          Deprecated. This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a charset name or that use the platform's default charset.
String(byte[] bytes, int offset, int length)
          Constructs a new String by decoding the specified subarray of bytes using the platform's default charset.
String(byte[] ascii, int hibyte, int offset, int count)
          Deprecated. This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a charset name or that use the platform's default charset.
String(byte[] bytes, int offset, int length, String charsetName)
          Constructs a new String by decoding the specified subarray of bytes using the specified charset.
String(byte[] bytes, String charsetName)
          Constructs a new String by decoding the specified array of bytes using the specified charset.
String(char[] value)
          Allocates a new String so that it represents the sequence of characters currently contained in the character array argument.
String(char[] value, int offset, int count)
          Allocates a new String that contains characters from a subarray of the character array argument.
String(String original)
          Initializes a newly created String object so that it represents the same sequence of characters as the argument; in other words, the newly created string is a copy of the argument string.
String(StringBuffer buffer)
          Allocates a new string that contains the sequence of characters currently contained in the string buffer argument.
 
Method Summary
 char charAt(int index)
          Returns the character at the specified index.
 int compareTo(Object o)
          Compares this String to another Object.
 int compareTo(String anotherString)
          Compares two strings lexicographically.
 int compareToIgnoreCase(String str)
          Compares two strings lexicographically, ignoring case differences.
 String concat(String str)
          Concatenates the specified string to the end of this string.
 boolean contentEquals(StringBuffer sb)
          Returns true if and only if this String represents the same sequence of characters as the specified StringBuffer.
static String copyValueOf(char[] data)
          Returns a String that represents the character sequence in the array specified.
static String copyValueOf(char[] data, int offset, int count)
          Returns a String that represents the character sequence in the array specified.
 boolean endsWith(String suffix)
          Tests if this string ends with the specified suffix.
 boolean equals(Object anObject)
          Compares this string to the specified object.
 boolean equalsIgnoreCase(String anotherString)
          Compares this String to another String, ignoring case considerations.
 byte[] getBytes()
          Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
 void getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin)
          Deprecated. This method does not properly convert characters into bytes. As of JDK 1.1, the preferred way to do this is via the the getBytes() method, which uses the platform's default charset.
 byte[] getBytes(String charsetName)
          Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.
 void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
          Copies characters from this string into the destination character array.
 int hashCode()
          Returns a hash code for this string.
 int indexOf(int ch)
          Returns the index within this string of the first occurrence of the specified character.
 int indexOf(int ch, int fromIndex)
          Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
 int indexOf(String str)
          Returns the index within this string of the first occurrence of the specified substring.
 int indexOf(String str, int fromIndex)
          Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
 String intern()
          Returns a canonical representation for the string object.
 int lastIndexOf(int ch)
          Returns the index within this string of the last occurrence of the specified character.
 int lastIndexOf(int ch, int fromIndex)
          Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.
 int lastIndexOf(String str)
          Returns the index within this string of the rightmost occurrence of the specified substring.
 int lastIndexOf(String str, int fromIndex)
          Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.
 int length()
          Returns the length of this string.
 boolean matches(String regex)
          Tells whether or not this string matches the given regular expression.
 boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)
          Tests if two string regions are equal.
 boolean regionMatches(int toffset, String other, int ooffset, int len)
          Tests if two string regions are equal.
 String replace(char oldChar, char newChar)
          Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
 String replaceAll(String regex, String replacement)
          Replaces each substring of this string that matches the given regular expression with the given replacement.
 String replaceFirst(String regex, String replacement)
          Replaces the first substring of this string that matches the given regular expression with the given replacement.
 String[] split(String regex)
          Splits this string around matches of the given regular expression.
 String[] split(String regex, int limit)
          Splits this string around matches of the given regular expression.
 boolean startsWith(String prefix)
          Tests if this string starts with the specified prefix.
 boolean startsWith(String prefix, int toffset)
          Tests if this string starts with the specified prefix beginning a specified index.
 CharSequence subSequence(int beginIndex, int endIndex)
          Returns a new character sequence that is a subsequence of this sequence.
 String substring(int beginIndex)
          Returns a new string that is a substring of this string.
 String substring(int beginIndex, int endIndex)
          Returns a new string that is a substring of this string.
 char[] toCharArray()
          Converts this string to a new character array.
 String toLowerCase()
          Converts all of the characters in this String to lower case using the rules of the default locale.
 String toLowerCase(Locale locale)
          Converts all of the characters in this String to lower case using the rules of the given Locale.
 String toString()
          This object (which is already a string!) is itself returned.
 String toUpperCase()
          Converts all of the characters in this String to upper case using the rules of the default locale.
 String toUpperCase(Locale locale)
          Converts all of the characters in this String to upper case using the rules of the given Locale.
 String trim()
          Returns a copy of the string, with leading and trailing whitespace omitted.
static String valueOf(boolean b)
          Returns the string representation of the boolean argument.
static String valueOf(char c)
          Returns the string representation of the char argument.
static String valueOf(char[] data)
          Returns the string representation of the char array argument.
static String valueOf(char[] data, int offset, int count)
          Returns the string representation of a specific subarray of the char array argument.
static String valueOf(double d)
          Returns the string representation of the double argument.
static String valueOf(float f)
          Returns the string representation of the float argument.
static String valueOf(int i)
          Returns the string representation of the int argument.
static String valueOf(long l)
          Returns the string representation of the long argument.
static String valueOf(Object obj)
          Returns the string representation of the Object argument.
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Field Detail

CASE_INSENSITIVE_ORDER

public static final Comparator CASE_INSENSITIVE_ORDER
A Comparator that orders String objects as by compareToIgnoreCase. This comparator is serializable.

Note that this Comparator does not take locale into account, and will result in an unsatisfactory ordering for certain locales. The java.text package provides Collators to allow locale-sensitive ordering.

Since:
1.2
See Also:
Collator.compare(String, String)
Constructor Detail

String

public String()
Initializes a newly created String object so that it represents an empty character sequence. Note that use of this constructor is unnecessary since Strings are immutable.


String

public String(String original)
Initializes a newly created String object so that it represents the same sequence of characters as the argument; in other words, the newly created string is a copy of the argument string. Unless an explicit copy of original is needed, use of this constructor is unnecessary since Strings are immutable.

Parameters:
original - a String.

String

public String(char[] value)
Allocates a new String so that it represents the sequence of characters currently contained in the character array argument. The contents of the character array are copied; subsequent modification of the character array does not affect the newly created string.

Parameters:
value - the initial value of the string.

String

public String(char[] value,
              int offset,
              int count)
Allocates a new String that contains characters from a subarray of the character array argument. The offset argument is the index of the first character of the subarray and the count argument specifies the length of the subarray. The contents of the subarray are copied; subsequent modification of the character array does not affect the newly created string.

Parameters:
value - array that is the source of characters.
offset - the initial offset.
count - the length.
Throws:
IndexOutOfBoundsException - if the offset and count arguments index characters outside the bounds of the value array.

String

public String(byte[] ascii,
              int hibyte,
              int offset,
              int count)
Deprecated. This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a charset name or that use the platform's default charset.

Allocates a new String constructed from a subarray of an array of 8-bit integer values.

The offset argument is the index of the first byte of the subarray, and the count argument specifies the length of the subarray.

Each byte in the subarray is converted to a char as specified in the method above.

Parameters:
ascii - the bytes to be converted to characters.
hibyte - the top 8 bits of each 16-bit Unicode character.
offset - the initial offset.
count - the length.
Throws:
IndexOutOfBoundsException - if the offset or count argument is invalid.
See Also:
String(byte[], int), String(byte[], int, int, java.lang.String), String(byte[], int, int), String(byte[], java.lang.String), String(byte[])

String

public String(byte[] ascii,
              int hibyte)
Deprecated. This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a charset name or that use the platform's default charset.

Allocates a new String containing characters constructed from an array of 8-bit integer values. Each character cin the resulting string is constructed from the corresponding component b in the byte array such that:

     c == (char)(((hibyte & 0xff) << 8)
                         | (b & 0xff))
 

Parameters:
ascii - the bytes to be converted to characters.
hibyte - the top 8 bits of each 16-bit Unicode character.
See Also:
String(byte[], int, int, java.lang.String), String(byte[], int, int), String(byte[], java.lang.String), String(byte[])

String

public String(byte[] bytes,
              int offset,
              int length,
              String charsetName)
       throws UnsupportedEncodingException
Constructs a new String by decoding the specified subarray of bytes using the specified charset. The length of the new String is a function of the charset, and hence may not be equal to the length of the subarray.

The behavior of this constructor when the given bytes are not valid in the given charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.

Parameters:
bytes - the bytes to be decoded into characters
offset - the index of the first byte to decode
length - the number of bytes to decode
charsetName - the name of a supported charset
Throws:
UnsupportedEncodingException - if the named charset is not supported
IndexOutOfBoundsException - if the offset and length arguments index characters outside the bounds of the bytes array
Since:
JDK1.1

String

public String(byte[] bytes,
              String charsetName)
       throws UnsupportedEncodingException
Constructs a new String by decoding the specified array of bytes using the specified charset. The length of the new String is a function of the charset, and hence may not be equal to the length of the byte array.

The behavior of this constructor when the given bytes are not valid in the given charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.

Parameters:
bytes - the bytes to be decoded into characters
charsetName - the name of a supported charset
Throws:
UnsupportedEncodingException - If the named charset is not supported
Since:
JDK1.1

String

public String(byte[] bytes,
              int offset,
              int length)
Constructs a new String by decoding the specified subarray of bytes using the platform's default charset. The length of the new String is a function of the charset, and hence may not be equal to the length of the subarray.

The behavior of this constructor when the given bytes are not valid in the default charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.

Parameters:
bytes - the bytes to be decoded into characters
offset - the index of the first byte to decode
length - the number of bytes to decode
Throws:
IndexOutOfBoundsException - if the offset and the length arguments index characters outside the bounds of the bytes array
Since:
JDK1.1

String

public String(byte[] bytes)
Constructs a new String by decoding the specified array of bytes using the platform's default charset. The length of the new String is a function of the charset, and hence may not be equal to the length of the byte array.

The behavior of this constructor when the given bytes are not valid in the default charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.

Parameters:
bytes - the bytes to be decoded into characters
Since:
JDK1.1

String

public String(StringBuffer buffer)
Allocates a new string that contains the sequence of characters currently contained in the string buffer argument. The contents of the string buffer are copied; subsequent modification of the string buffer does not affect the newly created string.

Parameters:
buffer - a StringBuffer.
Method Detail

length

public int length()
Returns the length of this string. The length is equal to the number of 16-bit Unicode characters in the string.

Specified by:
length in interface CharSequence
Returns:
the length of the sequence of characters represented by this object.

charAt

public char charAt(int index)
Returns the character at the specified index. An index ranges from 0 to length() - 1. The first character of the sequence is at index 0, the next at index 1, and so on, as for array indexing.

Specified by:
charAt in interface CharSequence
Parameters:
index - the index of the character.
Returns:
the character at the specified index of this string. The first character is at index 0.
Throws:
IndexOutOfBoundsException - if the index argument is negative or not less than the length of this string.

getChars

public void getChars(int srcBegin,
                     int srcEnd,
                     char[] dst,
                     int dstBegin)
Copies characters from this string into the destination character array.

The first character to be copied is at index srcBegin; the last character to be copied is at index srcEnd-1 (thus the total number of characters to be copied is srcEnd-srcBegin). The characters are copied into the subarray of dst starting at index dstBegin and ending at index:

     dstbegin + (srcEnd-srcBegin) - 1
 

Parameters:
srcBegin - index of the first character in the string to copy.
srcEnd - index after the last character in the string to copy.
dst - the destination array.
dstBegin - the start offset in the destination array.
Throws:
IndexOutOfBoundsException - If any of the following is true:
  • srcBegin is negative.
  • srcBegin is greater than srcEnd
  • srcEnd is greater than the length of this string
  • dstBegin is negative
  • dstBegin+(srcEnd-srcBegin) is larger than dst.length

getBytes

public void getBytes(int srcBegin,
                     int srcEnd,
                     byte[] dst,
                     int dstBegin)
Deprecated. This method does not properly convert characters into bytes. As of JDK 1.1, the preferred way to do this is via the the getBytes() method, which uses the platform's default charset.

Copies characters from this string into the destination byte array. Each byte receives the 8 low-order bits of the corresponding character. The eight high-order bits of each character are not copied and do not participate in the transfer in any way.

The first character to be copied is at index srcBegin; the last character to be copied is at index srcEnd-1. The total number of characters to be copied is srcEnd-srcBegin. The characters, converted to bytes, are copied into the subarray of dst starting at index dstBegin and ending at index:

     dstbegin + (srcEnd-srcBegin) - 1
 

Parameters:
srcBegin - index of the first character in the string to copy.
srcEnd - index after the last character in the string to copy.
dst - the destination array.
dstBegin - the start offset in the destination array.
Throws:
IndexOutOfBoundsException - if any of the following is true:
  • srcBegin is negative
  • srcBegin is greater than srcEnd
  • srcEnd is greater than the length of this String
  • dstBegin is negative
  • dstBegin+(srcEnd-srcBegin) is larger than dst.length

getBytes

public byte[] getBytes(String charsetName)
                throws UnsupportedEncodingException
Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.

The behavior of this method when this string cannot be encoded in the given charset is unspecified. The CharsetEncoder class should be used when more control over the encoding process is required.

Parameters:
charsetName - the name of a supported charset
Returns:
The resultant byte array
Throws:
UnsupportedEncodingException - If the named charset is not supported
Since:
JDK1.1

getBytes

public byte[] getBytes()
Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.

The behavior of this method when this string cannot be encoded in the default charset is unspecified. The CharsetEncoder class should be used when more control over the encoding process is required.

Returns:
The resultant byte array
Since:
JDK1.1

equals

public boolean equals(Object anObject)
Compares this string to the specified object. The result is true if and only if the argument is not null and is a String object that represents the same sequence of characters as this object.

Overrides:
equals in class Object
Parameters:
anObject - the object to compare this String against.
Returns:
true if the String are equal; false otherwise.
See Also:
compareTo(java.lang.String), equalsIgnoreCase(java.lang.String)

contentEquals

public boolean contentEquals(StringBuffer sb)
Returns true if and only if this String represents the same sequence of characters as the specified StringBuffer.

Parameters:
sb - the StringBuffer to compare to.
Returns:
true if and only if this String represents the same sequence of characters as the specified StringBuffer, otherwise false.
Since:
1.4

equalsIgnoreCase

public boolean equalsIgnoreCase(String anotherString)
Compares this String to another String, ignoring case considerations. Two strings are considered equal ignoring case if they are of the same length, and corresponding characters in the two strings are equal ignoring case.

Two characters c1 and c2 are considered the same, ignoring case if at least one of the following is true:

Parameters:
anotherString - the String to compare this String against.
Returns:
true if the argument is not null and the Strings are equal, ignoring case; false otherwise.
See Also:
equals(Object), Character.toLowerCase(char), Character.toUpperCase(char)

compareTo

public int compareTo(String anotherString)
Compares two strings lexicographically. The comparison is based on the Unicode value of each character in the strings. The character sequence represented by this String object is compared lexicographically to the character sequence represented by the argument string. The result is a negative integer if this String object lexicographically precedes the argument string. The result is a positive integer if this String object lexicographically follows the argument string. The result is zero if the strings are equal; compareTo returns 0 exactly when the equals(Object) method would return true.

This is the definition of lexicographic ordering. If two strings are different, then either they have different characters at some index that is a valid index for both strings, or their lengths are different, or both. If they have different characters at one or more index positions, let k be the smallest such index; then the string whose character at position k has the smaller value, as determined by using the < operator, lexicographically precedes the other string. In this case, compareTo returns the difference of the two character values at position k in the two string -- that is, the value:

 this.charAt(k)-anotherString.charAt(k)
 
If there is no index position at which they differ, then the shorter string lexicographically precedes the longer string. In this case, compareTo returns the difference of the lengths of the strings -- that is, the value:
 this.length()-anotherString.length()
 

Parameters:
anotherString - the String to be compared.
Returns:
the value 0 if the argument string is equal to this string; a value less than 0 if this string is lexicographically less than the string argument; and a value greater than 0 if this string is lexicographically greater than the string argument.

compareTo

public int compareTo(Object o)
Compares this String to another Object. If the Object is a String, this function behaves like compareTo(String). Otherwise, it throws a ClassCastException (as Strings are comparable only to other Strings).

Specified by:
compareTo in interface Comparable
Parameters:
o - the Object to be compared.
Returns:
the value 0 if the argument is a string lexicographically equal to this string; a value less than 0 if the argument is a string lexicographically greater than this string; and a value greater than 0 if the argument is a string lexicographically less than this string.
Throws:
ClassCastException - if the argument is not a String.
Since:
1.2
See Also:
Comparable

compareToIgnoreCase

public int compareToIgnoreCase(String str)
Compares two strings lexicographically, ignoring case differences. This method returns an integer whose sign is that of calling compareTo with normalized versions of the strings where case differences have been eliminated by calling Character.toLowerCase(Character.toUpperCase(character)) on each character.

Note that this method does not take locale into account, and will result in an unsatisfactory ordering for certain locales. The java.text package provides collators to allow locale-sensitive ordering.

Parameters:
str - the String to be compared.
Returns:
a negative integer, zero, or a positive integer as the the specified String is greater than, equal to, or less than this String, ignoring case considerations.
Since:
1.2
See Also:
Collator.compare(String, String)

regionMatches

public boolean regionMatches(int toffset,
                             String other,
                             int ooffset,
                             int len)
Tests if two string regions are equal.

A substring of this String object is compared to a substring of the argument other. The result is true if these substrings represent identical character sequences. The substring of this String object to be compared begins at index toffset and has length len. The substring of other to be compared begins at index ooffset and has length len. The result is false if and only if at least one of the following is true:

Parameters:
toffset - the starting offset of the subregion in this string.
other - the string argument.
ooffset - the starting offset of the subregion in the string argument.
len - the number of characters to compare.
Returns:
true if the specified subregion of this string exactly matches the specified subregion of the string argument; false otherwise.

regionMatches

public boolean regionMatches(boolean ignoreCase,
                             int toffset,
                             String other,
                             int ooffset,
                             int len)
Tests if two string regions are equal.

A substring of this String object is compared to a substring of the argument other. The result is true if these substrings represent character sequences that are the same, ignoring case if and only if ignoreCase is true. The substring of this String object to be compared begins at index toffset and has length len. The substring of other to be compared begins at index ooffset and has length len. The result is false if and only if at least one of the following is true:

Parameters:
ignoreCase - if true, ignore case when comparing characters.
toffset - the starting offset of the subregion in this string.
other - the string argument.
ooffset - the starting offset of the subregion in the string argument.
len - the number of characters to compare.
Returns:
true if the specified subregion of this string matches the specified subregion of the string argument; false otherwise. Whether the matching is exact or case insensitive depends on the ignoreCase argument.

startsWith

public boolean startsWith(String prefix,
                          int toffset)
Tests if this string starts with the specified prefix beginning a specified index.

Parameters:
prefix - the prefix.
toffset - where to begin looking in the string.
Returns:
true if the character sequence represented by the argument is a prefix of the substring of this object starting at index toffset; false otherwise. The result is false if toffset is negative or greater than the length of this String object; otherwise the result is the same as the result of the expression
          this.subString(toffset).startsWith(prefix)
          

startsWith

public boolean startsWith(String prefix)
Tests if this string starts with the specified prefix.

Parameters:
prefix - the prefix.
Returns:
true if the character sequence represented by the argument is a prefix of the character sequence represented by this string; false otherwise. Note also that true will be returned if the argument is an empty string or is equal to this String object as determined by the equals(Object) method.
Since:
1. 0

endsWith

public boolean endsWith(String suffix)
Tests if this string ends with the specified suffix.

Parameters:
suffix - the suffix.
Returns:
true if the character sequence represented by the argument is a suffix of the character sequence represented by this object; false otherwise. Note that the result will be true if the argument is the empty string or is equal to this String object as determined by the equals(Object) method.

hashCode

public int hashCode()
Returns a hash code for this string. The hash code for a String object is computed as
 s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
 
using int arithmetic, where s[i] is the ith character of the string, n is the length of the string, and ^ indicates exponentiation. (The hash value of the empty string is zero.)

Overrides:
hashCode in class Object
Returns:
a hash code value for this object.
See Also:
Object.equals(java.lang.Object), Hashtable

indexOf

public int indexOf(int ch)
Returns the index within this string of the first occurrence of the specified character. If a character with value ch occurs in the character sequence represented by this String object, then the index of the first such occurrence is returned -- that is, the smallest value k such that:
 this.charAt(k) == ch
 
is true. If no such character occurs in this string, then -1 is returned.

Parameters:
ch - a character.
Returns:
the index of the first occurrence of the character in the character sequence represented by this object, or -1 if the character does not occur.

indexOf

public int indexOf(int ch,
                   int fromIndex)
Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.

If a character with value ch occurs in the character sequence represented by this String object at an index no smaller than fromIndex, then the index of the first such occurrence is returned--that is, the smallest value k such that:

 (this.charAt(k) == ch) && (k >= fromIndex)
 
is true. If no such character occurs in this string at or after position fromIndex, then -1 is returned.

There is no restriction on the value of fromIndex. If it is negative, it has the same effect as if it were zero: this entire string may be searched. If it is greater than the length of this string, it has the same effect as if it were equal to the length of this string: -1 is returned.

Parameters:
ch - a character.
fromIndex - the index to start the search from.
Returns:
the index of the first occurrence of the character in the character sequence represented by this object that is greater than or equal to fromIndex, or -1 if the character does not occur.

lastIndexOf

public int lastIndexOf(int ch)
Returns the index within this string of the last occurrence of the specified character. That is, the index returned is the largest value k such that:
 this.charAt(k) == ch
 
is true. The String is searched backwards starting at the last character.

Parameters:
ch - a character.
Returns:
the index of the last occurrence of the character in the character sequence represented by this object, or -1 if the character does not occur.

lastIndexOf

public int lastIndexOf(int ch,
                       int fromIndex)
Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index. That is, the index returned is the largest value k such that:
 this.charAt(k) == ch) && (k <= fromIndex)
 
is true.

Parameters:
ch - a character.
fromIndex - the index to start the search from. There is no restriction on the value of fromIndex. If it is greater than or equal to the length of this string, it has the same effect as if it were equal to one less than the length of this string: this entire string may be searched. If it is negative, it has the same effect as if it were -1: -1 is returned.
Returns:
the index of the last occurrence of the character in the character sequence represented by this object that is less than or equal to fromIndex, or -1 if the character does not occur before that point.

indexOf

public int indexOf(String str)
Returns the index within this string of the first occurrence of the specified substring. The integer returned is the smallest value k such that:
 this.startsWith(str, k)
 
is true.

Parameters:
str - any string.
Returns:
if the string argument occurs as a substring within this object, then the index of the first character of the first such substring is returned; if it does not occur as a substring, -1 is returned.

indexOf

public int indexOf(String str,
                   int fromIndex)
Returns the index within this string of the first occurrence of the specified substring, starting at the specified index. The integer returned is the smallest value k for which:
     k >= Math.min(fromIndex, str.length()) && this.startsWith(str, k)
 
If no such value of k exists, then -1 is returned.

Parameters:
str - the substring for which to search.
fromIndex - the index from which to start the search.
Returns:
the index within this string of the first occurrence of the specified substring, starting at the specified index.

lastIndexOf

public int lastIndexOf(String str)
Returns the index within this string of the rightmost occurrence of the specified substring. The rightmost empty string "" is considered to occur at the index value this.length(). The returned index is the largest value k such that
 this.startsWith(str, k)
 
is true.

Parameters:
str - the substring to search for.
Returns:
if the string argument occurs one or more times as a substring within this object, then the index of the first character of the last such substring is returned. If it does not occur as a substring, -1 is returned.

lastIndexOf

public int lastIndexOf(String str,
                       int fromIndex)
Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index. The integer returned is the largest value k such that:
     k <= Math.min(fromIndex, str.length()) && this.startsWith(str, k)
 
If no such value of k exists, then -1 is returned.

Parameters:
str - the substring to search for.
fromIndex - the index to start the search from.
Returns:
the index within this string of the last occurrence of the specified substring.

substring

public String substring(int beginIndex)
Returns a new string that is a substring of this string. The substring begins with the character at the specified index and extends to the end of this string.

Examples:

 "unhappy".substring(2) returns "happy"
 "Harbison".substring(3) returns "bison"
 "emptiness".substring(9) returns "" (an empty string)
 

Parameters:
beginIndex - the beginning index, inclusive.
Returns:
the specified substring.
Throws:
IndexOutOfBoundsException - if beginIndex is negative or larger than the length of this String object.

substring

public String substring(int beginIndex,
                        int endIndex)
Returns a new string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is endIndex-beginIndex.

Examples:

 "hamburger".substring(4, 8) returns "urge"
 "smiles".substring(1, 5) returns "mile"
 

Parameters:
beginIndex - the beginning index, inclusive.
endIndex - the ending index, exclusive.
Returns:
the specified substring.
Throws:
IndexOutOfBoundsException - if the beginIndex is negative, or endIndex is larger than the length of this String object, or beginIndex is larger than endIndex.

subSequence

public CharSequence subSequence(int beginIndex,
                                int endIndex)
Returns a new character sequence that is a subsequence of this sequence.

An invocation of this method of the form

 str.subSequence(begin, end)
behaves in exactly the same way as the invocation
 str.substring(begin, end)
This method is defined so that the String class can implement the CharSequence interface.

Specified by:
subSequence in interface CharSequence
Parameters:
beginIndex - the begin index, inclusive.
endIndex - the end index, exclusive.
Returns:
the specified subsequence.
Throws:
IndexOutOfBoundsException - if beginIndex or endIndex are negative, if endIndex is greater than length(), or if beginIndex is greater than startIndex
Since:
1.4

concat

public String concat(String str)
Concatenates the specified string to the end of this string.

If the length of the argument string is 0, then this String object is returned. Otherwise, a new String object is created, representing a character sequence that is the concatenation of the character sequence represented by this String object and the character sequence represented by the argument string.

Examples:

 "cares".concat("s") returns "caress"
 "to".concat("get").concat("her") returns "together"
 

Parameters:
str - the String that is concatenated to the end of this String.
Returns:
a string that represents the concatenation of this object's characters followed by the string argument's characters.

replace

public String replace(char oldChar,
                      char newChar)
Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.

If the character oldChar does not occur in the character sequence represented by this String object, then a reference to this String object is returned. Otherwise, a new String object is created that represents a character sequence identical to the character sequence represented by this String object, except that every occurrence of oldChar is replaced by an occurrence of newChar.

Examples:

 "mesquite in your cellar".replace('e', 'o')
         returns "mosquito in your collar"
 "the war of baronets".replace('r', 'y')
         returns "the way of bayonets"
 "sparring with a purple porpoise".replace('p', 't')
         returns "starring with a turtle tortoise"
 "JonL".replace('q', 'x') returns "JonL" (no change)
 

Parameters:
oldChar - the old character.
newChar - the new character.
Returns:
a string derived from this string by replacing every occurrence of oldChar with newChar.

matches

public boolean matches(String regex)
Tells whether or not this string matches the given regular expression.

An invocation of this method of the form str.matches(regex) yields exactly the same result as the expression

Pattern.matches(regex, str)

Parameters:
regex - the regular expression to which this string is to be matched
Returns:
true if, and only if, this string matches the given regular expression
Throws:
PatternSyntaxException - if the regular expression's syntax is invalid
Since:
1.4
See Also:
Pattern

replaceFirst

public String replaceFirst(String regex,
                           String replacement)
Replaces the first substring of this string that matches the given regular expression with the given replacement.

An invocation of this method of the form str.replaceFirst(regex, repl) yields exactly the same result as the expression

Pattern.compile(regex).matcher(str).replaceFirst(repl)

Parameters:
regex - the regular expression to which this string is to be matched
Returns:
The resulting String
Throws:
PatternSyntaxException - if the regular expression's syntax is invalid
Since:
1.4
See Also:
Pattern

replaceAll

public String replaceAll(String regex,
                         String replacement)
Replaces each substring of this string that matches the given regular expression with the given replacement.

An invocation of this method of the form str.replaceAll(regex, repl) yields exactly the same result as the expression

Pattern.compile(regex).matcher(str).replaceAll(repl)

Parameters:
regex - the regular expression to which this string is to be matched
Returns:
The resulting String
Throws:
PatternSyntaxException - if the regular expression's syntax is invalid
Since:
1.4
See Also:
Pattern

split

public String[] split(String regex,
                      int limit)
Splits this string around matches of the given regular expression.

The array returned by this method contains each substring of this string that is terminated by another substring that matches the given expression or is terminated by the end of the string. The substrings in the array are in the order in which they occur in this string. If the expression does not match any part of the input then the resulting array has just one element, namely this string.

The limit parameter controls the number of times the pattern is applied and therefore affects the length of the resulting array. If the limit n is greater than zero then the pattern will be applied at most n - 1 times, the array's length will be no greater than n, and the array's last entry will contain all input beyond the last matched delimiter. If n is non-positive then the pattern will be applied as many times as possible and the array can have any length. If n is zero then the pattern will be applied as many times as possible, the array can have any length, and trailing empty strings will be discarded.

The string "boo:and:foo", for example, yields the following results with these parameters:

Regex Limit Result
: 2 { "boo", "and:foo" }
: 5 { "boo", "and", "foo" }
: -2 { "boo", "and", "foo" }
o 5 { "b", "", ":and:f", "", "" }
o -2 { "b", "", ":and:f", "", "" }
o 0 { "b", "", ":and:f" }

An invocation of this method of the form str.split(regex, n) yields the same result as the expression

Pattern.compile(regex).split(str, n)

Parameters:
regex - the delimiting regular expression
limit - the result threshold, as described above
Returns:
the array of strings computed by splitting this string around matches of the given regular expression
Throws:
PatternSyntaxException - if the regular expression's syntax is invalid
Since:
1.4
See Also:
Pattern

split

public String[] split(String regex)
Splits this string around matches of the given regular expression.

This method works as if by invoking the two-argument split method with the given expression and a limit argument of zero. Trailing empty strings are therefore not included in the resulting array.

The string "boo:and:foo", for example, yields the following results with these expressions:

Regex Result
: { "boo", "and", "foo" }
o { "b", "", ":and:f" }

Parameters:
regex - the delimiting regular expression
Returns:
the array of strings computed by splitting this string around matches of the given regular expression
Throws:
PatternSyntaxException - if the regular expression's syntax is invalid
Since:
1.4
See Also:
Pattern

toLowerCase

public String toLowerCase(Locale locale)
Converts all of the characters in this String to lower case using the rules of the given Locale. Case mappings rely heavily on the Unicode specification's character data. Since case mappings are not always 1:1 char mappings, the resulting String may be a different length than the original String.

Examples of lowercase mappings are in the following table:

Language Code of Locale Upper Case Lower Case Description
tr (Turkish) \u0130 \u0069 capital letter I with dot above -> small letter i
tr (Turkish) \u0049 \u0131 capital letter I -> small letter dotless i
(all) French Fries french fries lowercased all chars in String
(all) capiotacapchi capthetacapupsil capsigma iotachi thetaupsilon sigma lowercased all chars in String

Parameters:
locale - use the case transformation rules for this locale
Returns:
the String, converted to lowercase.
Since:
1.1
See Also:
toLowerCase(), toUpperCase(), toUpperCase(Locale)

toLowerCase

public String toLowerCase()
Converts all of the characters in this String to lower case using the rules of the default locale. This is equivalent to calling toLowerCase(Locale.getDefault()).

Returns:
the String, converted to lowercase.
See Also:
toLowerCase(Locale)

toUpperCase

public String toUpperCase(Locale locale)
Converts all of the characters in this String to upper case using the rules of the given Locale. Case mappings rely heavily on the Unicode specification's character data. Since case mappings are not always 1:1 char mappings, the resulting String may be a different length than the original String.

Examples of locale-sensitive and 1:M case mappings are in the following table.

Language Code of Locale Lower Case Upper Case Description
tr (Turkish) \u0069 \u0130 small letter i -> capital letter I with dot above
tr (Turkish) \u0131 \u0049 small letter dotless i -> capital letter I
(all) \u00df \u0053 \u0053 small letter sharp s -> two letters: SS
(all) Fahrvergnügen FAHRVERGNÜGEN

Parameters:
locale - use the case transformation rules for this locale
Returns:
the String, converted to uppercase.
Since:
1.1
See Also:
toUpperCase(), toLowerCase(), toLowerCase(Locale)

toUpperCase

public String toUpperCase()
Converts all of the characters in this String to upper case using the rules of the default locale. This method is equivalent to toUpperCase(Locale.getDefault()).

Returns:
the String, converted to uppercase.
See Also:
toUpperCase(Locale)

trim

public String trim()
Returns a copy of the string, with leading and trailing whitespace omitted.

If this String object represents an empty character sequence, or the first and last characters of character sequence represented by this String object both have codes greater than '\u0020' (the space character), then a reference to this String object is returned.

Otherwise, if there is no character with a code greater than '\u0020' in the string, then a new String object representing an empty string is created and returned.

Otherwise, let k be the index of the first character in the string whose code is greater than '\u0020', and let m be the index of the last character in the string whose code is greater than '\u0020'. A new String object is created, representing the substring of this string that begins with the character at index k and ends with the character at index m-that is, the result of this.substring(km+1).

This method may be used to trim whitespace from the beginning and end of a string; in fact, it trims all ASCII control characters as well.

Returns:
A copy of this string with leading and trailing white space removed, or this string if it has no leading or trailing white space.

toString

public String toString()
This object (which is already a string!) is itself returned.

Specified by:
toString in interface CharSequence
Overrides:
toString in class Object
Returns:
the string itself.

toCharArray

public char[] toCharArray()
Converts this string to a new character array.

Returns:
a newly allocated character array whose length is the length of this string and whose contents are initialized to contain the character sequence represented by this string.

valueOf

public static String valueOf(Object obj)
Returns the string representation of the Object argument.

Parameters:
obj - an Object.
Returns:
if the argument is null, then a string equal to "null"; otherwise, the value of obj.toString() is returned.
See Also:
Object.toString()

valueOf

public static String valueOf(char[] data)
Returns the string representation of the char array argument. The contents of the character array are copied; subsequent modification of the character array does not affect the newly created string.

Parameters:
data - a char array.
Returns:
a newly allocated string representing the same sequence of characters contained in the character array argument.

valueOf

public static String valueOf(char[] data,
                             int offset,
                             int count)
Returns the string representation of a specific subarray of the char array argument.

The offset argument is the index of the first character of the subarray. The count argument specifies the length of the subarray. The contents of the subarray are copied; subsequent modification of the character array does not affect the newly created string.

Parameters:
data - the character array.
offset - the initial offset into the value of the String.
count - the length of the value of the String.
Returns:
a string representing the sequence of characters contained in the subarray of the character array argument.
Throws:
IndexOutOfBoundsException - if offset is negative, or count is negative, or offset+count is larger than data.length.

copyValueOf

public static String copyValueOf(char[] data,
                                 int offset,
                                 int count)
Returns a String that represents the character sequence in the array specified.

Parameters:
data - the character array.
offset - initial offset of the subarray.
count - length of the subarray.
Returns:
a String that contains the characters of the specified subarray of the character array.

copyValueOf

public static String copyValueOf(char[] data)
Returns a String that represents the character sequence in the array specified.

Parameters:
data - the character array.
Returns:
a String that contains the characters of the character array.

valueOf

public static String valueOf(boolean b)
Returns the string representation of the boolean argument.

Parameters:
b - a boolean.
Returns:
if the argument is true, a string equal to "true" is returned; otherwise, a string equal to "false" is returned.

valueOf

public static String valueOf(char c)
Returns the string representation of the char argument.

Parameters:
c - a char.
Returns:
a string of length 1 containing as its single character the argument c.

valueOf

public static String valueOf(int i)
Returns the string representation of the int argument.

The representation is exactly the one returned by the Integer.toString method of one argument.

Parameters:
i - an int.
Returns:
a string representation of the int argument.
See Also:
Integer.toString(int, int)

valueOf

public static String valueOf(long l)
Returns the string representation of the long argument.

The representation is exactly the one returned by the Long.toString method of one argument.

Parameters:
l - a long.
Returns:
a string representation of the long argument.
See Also:
Long.toString(long)

valueOf

public static String valueOf(float f)
Returns the string representation of the float argument.

The representation is exactly the one returned by the Float.toString method of one argument.

Parameters:
f - a float.
Returns:
a string representation of the float argument.
See Also:
Float.toString(float)

valueOf

public static String valueOf(double d)
Returns the string representation of the double argument.

The representation is exactly the one returned by the Double.toString method of one argument.

Parameters:
d - a double.
Returns:
a string representation of the double argument.
See Also:
Double.toString(double)

intern

public String intern()
Returns a canonical representation for the string object.

A pool of strings, initially empty, is maintained privately by the class String.

When the intern method is invoked, if the pool already contains a string equal to this String object as determined by the equals(Object) method, then the string from the pool is returned. Otherwise, this String object is added to the pool and a reference to this String object is returned.

It follows that for any two strings s and t, s.intern() == t.intern() is true if and only if s.equals(t) is true.

All literal strings and string-valued constant expressions are interned. String literals are defined in §3.10.5 of the Java Language Specification

Returns:
a string that has the same contents as this string, but is guaranteed to be from a pool of unique strings.

JavaTM 2 Platform
Std. Ed. v1.4.2

Submit a bug or feature
For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2003 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.


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