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/* -*- Mode: java; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
package org.mozilla.javascript;
import java.io.Serializable;
/**
* This class implements the Undefined value in JavaScript.
*
* We represent "undefined" internally using two static objects -- "Undefined.instance" and
* SCRIPTABLE_UNDEFINED. Java code that needs to make something undefined should generally use the
* first, and use the second if a Scriptable object is absolutely required.
*
*
Java code that needs to test whether something is undefined must use the "isUndefined"
* method because of the multiple internal representations.
*/
public class Undefined implements Serializable {
private static final long serialVersionUID = 9195680630202616767L;
/**
* This is the standard value for "undefined" in Rhino. Java code that needs to represent
* "undefined" should use this object (rather than a new instance of this class).
*/
public static final Object instance = new Undefined();
private static final int instanceHash = System.identityHashCode(instance);
private Undefined() {}
public Object readResolve() {
return instance;
}
@Override
public boolean equals(Object obj) {
return isUndefined(obj) || super.equals(obj);
}
@Override
public int hashCode() {
// All instances of Undefined are equivalent!
return instanceHash;
}
/**
* An alternate representation of undefined, to be used only when we need to pass it to a method
* that takes as Scriptable as a parameter. This is used when we need to pass undefined as the
* "this" parmeter of a Callable instance, because we cannot change that interface without
* breaking backward compatibility.
*/
public static final Scriptable SCRIPTABLE_UNDEFINED =
new Scriptable() {
@Override
public String getClassName() {
return "undefined";
}
@Override
public Object get(String name, Scriptable start) {
return NOT_FOUND;
}
@Override
public Object get(int index, Scriptable start) {
return NOT_FOUND;
}
@Override
public boolean has(String name, Scriptable start) {
return false;
}
@Override
public boolean has(int index, Scriptable start) {
return false;
}
@Override
public void put(String name, Scriptable start, Object value) {}
@Override
public void put(int index, Scriptable start, Object value) {}
@Override
public void delete(String name) {}
@Override
public void delete(int index) {}
@Override
public Scriptable getPrototype() {
return null;
}
@Override
public void setPrototype(Scriptable prototype) {}
@Override
public Scriptable getParentScope() {
return null;
}
@Override
public void setParentScope(Scriptable parent) {}
@Override
public Object[] getIds() {
return ScriptRuntime.emptyArgs;
}
@Override
public Object getDefaultValue(Class hint) {
if (hint == null || hint == ScriptRuntime.StringClass) {
return toString();
}
return null;
}
@Override
public boolean hasInstance(Scriptable instance) {
return false;
}
@Override
public String toString() {
return "undefined";
}
@Override
public boolean equals(Object obj) {
return isUndefined(obj) || super.equals(obj);
}
@Override
public int hashCode() {
return instanceHash;
}
};
/**
* Safely test whether "obj" is undefined. Java code must use this function rather than testing
* the value directly since we have two representations of undefined in Rhino.
*/
public static boolean isUndefined(Object obj) {
return Undefined.instance == obj || Undefined.SCRIPTABLE_UNDEFINED == obj;
}
}