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	/*
	* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.beans;

	/**
	* An <code>Expression</code> 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 <code>"a.getFoo()"</code>.
	* <p>
	* In addition to the properties of the super class, the
	* <code>Expression</code> object provides a <em>value</em> 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 <code>getValue</code> is made.
	*
	* @see #getValue
	* @see #setValue
	*
	* @since 1.4
	*
	* @author Philip Milne
	*/
	public class Expression extends Statement {

	private static Object unbound = new Object();

	private Object value = unbound;

	/**
	* Creates a new {@link Expression} object
	* for the specified target object to invoke the method
	* specified by the name and by the array of arguments.
	* <p>
	* 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.
	*
	* @param target the target object of this expression
	* @param methodName the name of the method to invoke on the specified target
	* @param arguments the array of arguments to invoke the specified method
	*
	* @see #getValue
	*/
	@ConstructorProperties({"target", "methodName", "arguments"})
	public Expression(Object target, String methodName, Object[] arguments) {
	super(target, methodName, arguments);
	}

	/**
	* Creates a new {@link 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 {@link #getValue} method will return it
	* without executing this {@code Expression}.
	* <p>
	* 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.
	*
	* @param value the value of this expression
	* @param target the target object of this expression
	* @param methodName the name of the method to invoke on the specified target
	* @param arguments the array of arguments to invoke the specified method
	*
	* @see #setValue
	*/
	public Expression(Object value, Object target, String methodName, Object[] arguments) {
	this(target, methodName, arguments);
	setValue(value);
	}

	/**
	* {@inheritDoc}
	* <p>
	* 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}.
	*
	* @throws NullPointerException if the value of the {@code target} or
	* {@code methodName} property is {@code null}
	* @throws NoSuchMethodException if a matching method is not found
	* @throws SecurityException if a security manager exists and
	* it denies the method invocation
	* @throws Exception that is thrown by the invoked method
	*
	* @see java.lang.reflect.Method
	* @since 1.7
	*/
	@Override
	public void execute() throws Exception {
	setValue(invoke());
	}

	/**
	* 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 <code>getValue</code>. If the value property
	* was already set, either by a call to <code>setValue</code>
	* or a previous call to <code>getValue</code> then the value
	* property is returned without either looking up or calling the method.
	* <p>
	* The value property of an <code>Expression</code> is set to
	* a unique private (non-<code>null</code>) value by default and
	* this value is used as an internal indication that the method
	* has not yet been called. A return value of <code>null</code>
	* replaces this default value in the same way that any other value
	* would, ensuring that expressions are never evaluated more than once.
	* <p>
	* See the <code>execute</code> method for details on how
	* methods are chosen using the dynamic types of the target
	* and arguments.
	*
	* @see Statement#execute
	* @see #setValue
	*
	* @return The result of applying this method to these arguments.
	* @throws Exception if the method with the specified methodName
	* throws an exception
	*/
	public Object getValue() throws Exception {
	if (value == unbound) {
	setValue(invoke());
	}
	return value;
	}

	/**
	* Sets the value of this expression to <code>value</code>.
	* This value will be returned by the getValue method
	* without calling the method associated with this
	* expression.
	*
	* @param value The value of this expression.
	*
	* @see #getValue
	*/
	public void setValue(Object value) {
	this.value = value;
	}

	/pp/ String instanceName(Object instance) {
	return instance == unbound ? "<unbound>" : super.instanceName(instance);
	}

	/**
	* Prints the value of this expression using a Java-style syntax.
	*/
	public String toString() {
	return instanceName(value) + "=" + super.toString();
	}
	}

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