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java.beans
public class: Expression [javadoc | source]
java.lang.Object
   java.beans.Statement
      java.beans.Expression
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.

Fields inherited from java.beans.Statement:
defaultExceptionListener,  loader
Constructor:
 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 {@code target} and the {@code methodName} values should not be {@code null}. Otherwise an attempt to execute this {@code Expression} will result in a {@code NullPointerException}. If the {@code arguments} value is {@code null}, an empty array is used as the value of the {@code 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
    Also see:
    getValue
 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 {@code value} value is used as the value of the {@code value} property, so the #getValue method will return it without executing this {@code Expression}.

    The {@code target} and the {@code methodName} values should not be {@code null}. Otherwise an attempt to execute this {@code Expression} will result in a {@code NullPointerException}. If the {@code arguments} value is {@code null}, an empty array is used as the value of the {@code 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
    Also see:
    setValue
Method from java.beans.Expression Summary:
execute,   getValue,   instanceName,   setValue,   toString
Methods from java.beans.Statement:
execute,   getArguments,   getMethod,   getMethodName,   getTarget,   instanceName,   invoke,   toString
Methods from java.lang.Object:
clone,   equals,   finalize,   getClass,   hashCode,   notify,   notifyAll,   toString,   wait,   wait,   wait
Method from java.beans.Expression Detail:
 public  void execute() throws Exception 
    {@inheritDoc}

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

 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.

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