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Java™ Platform
Standard Ed. 7

DRAFT ea-b118

java.beans
Class Expression

java.lang.Object
  extended by java.beans.Statement
      extended by java.beans.Expression

public class Expression
extends Statement

An Expression object represents a primitive expression in which a single method is applied to a target and a set of arguments to return a result - as in "a.getFoo()".

In addition to the properties of the super class, the Expression object provides a value which is the object returned when this expression is evaluated. The return value is typically not provided by the caller and is instead computed by dynamically finding the method and invoking it when the first call to getValue is made.

Since:
1.4
See Also:
getValue(), setValue(java.lang.Object)

Constructor Summary
Constructor and Description
Expression(Object value, Object target, String methodName, Object[] arguments)
          Creates a new Expression object with the specified value for the specified target object to invoke the method specified by the name and by the array of arguments.
Expression(Object target, String methodName, Object[] arguments)
          Creates a new Expression object for the specified target object to invoke the method specified by the name and by the array of arguments.
 
Method Summary
Modifier and Type Method and Description
 void execute()
          The execute method finds a method whose name is the same as the methodName property, and invokes the method on the target.
 Object getValue()
          If the value property of this instance is not already set, this method dynamically finds the method with the specified methodName on this target with these arguments and calls it.
 void setValue(Object value)
          Sets the value of this expression to value.
 String toString()
          Prints the value of this expression using a Java-style syntax.
 
Methods inherited from class java.beans.Statement
getArguments, getMethodName, getTarget
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

Expression

@ConstructorProperties(value={"target","methodName","arguments"})
public Expression(Object target,
                                             String methodName,
                                             Object[] arguments)
Creates a new Expression object for the specified target object to invoke the method specified by the name and by the array of arguments.

The target and the methodName values should not be null. Otherwise an attempt to execute this Expression will result in a NullPointerException. If the arguments value is null, an empty array is used as the value of the arguments property.

Parameters:
target - the target object of this expression
methodName - the name of the method to invoke on the specified target
arguments - the array of arguments to invoke the specified method
See Also:
getValue()

Expression

public Expression(Object value,
                  Object target,
                  String methodName,
                  Object[] arguments)
Creates a new Expression object with the specified value for the specified target object to invoke the method specified by the name and by the array of arguments. The value value is used as the value of the value property, so the getValue() method will return it without executing this Expression.

The target and the methodName values should not be null. Otherwise an attempt to execute this Expression will result in a NullPointerException. If the arguments value is null, an empty array is used as the value of the arguments property.

Parameters:
value - the value of this expression
target - the target object of this expression
methodName - the name of the method to invoke on the specified target
arguments - the array of arguments to invoke the specified method
See Also:
setValue(java.lang.Object)
Method Detail

execute

public void execute()
             throws Exception
The execute method finds a method whose name is the same as the methodName property, and invokes the method on the target. When the target's class defines many methods with the given name the implementation should choose the most specific method using the algorithm specified in the Java Language Specification (15.11). The dynamic class of the target and arguments are used in place of the compile-time type information and, like the Method class itself, conversion between primitive values and their associated wrapper classes is handled internally.

The following method types are handled as special cases:

If the invoked method completes normally, the value it returns is copied in the value property. Note that the value property is set to null, if the return type of the underlying method is void.

Overrides:
execute in class Statement
Throws:
NullPointerException - if the value of the target or methodName property is null
NoSuchMethodException - if a matching method is not found
SecurityException - if a security manager exists and it denies the method invocation
Exception - that is thrown by the invoked method
Since:
1.7
See Also:
Method

getValue

public Object getValue()
                throws Exception
If the value property of this instance is not already set, this method dynamically finds the method with the specified methodName on this target with these arguments and calls it. The result of the method invocation is first copied into the value property of this expression and then returned as the result of getValue. If the value property was already set, either by a call to setValue or a previous call to getValue then the value property is returned without either looking up or calling the method.

The value property of an Expression is set to a unique private (non-null) value by default and this value is used as an internal indication that the method has not yet been called. A return value of null replaces this default value in the same way that any other value would, ensuring that expressions are never evaluated more than once.

See the excecute method for details on how methods are chosen using the dynamic types of the target and arguments.

Returns:
The result of applying this method to these arguments.
Throws:
Exception
See Also:
Statement.execute(), setValue(java.lang.Object)

setValue

public void setValue(Object value)
Sets the value of this expression to value. This value will be returned by the getValue method without calling the method associated with this expression.

Parameters:
value - The value of this expression.
See Also:
getValue()

toString

public String toString()
Prints the value of this expression using a Java-style syntax.

Overrides:
toString in class Statement
Returns:
a string representation of the object.

Java™ Platform
Standard Ed. 7

DRAFT ea-b118

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For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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DRAFT ea-b118

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