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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

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 * 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,

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 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

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>excecute</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.

     */

    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();

    }

}