Java example source code file (UseBeforeDeclaration.java)

This example Java source code file (UseBeforeDeclaration.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

object, usebeforedeclaration

The UseBeforeDeclaration.java Java example source code

/*
 * Copyright (c) 2002, 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.
 *
 * 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.
 */

/*
 * @test
 * @bug 4459133
 * @summary Forward reference legal or illegal?
 * @author gafter
 *
 * @compile UseBeforeDeclaration.java
 */

class UseBeforeDeclaration {
    static {
        x = 100; // ok - assignment
//      int y = ((x)) + 1; // error - read before declaration
        int v = ((x)) = 3; // ok - x at left hand side of assignment
        int z = UseBeforeDeclaration.x * 2; // ok - not accessed via simple name
        Object o = new Object(){
                void foo(){x++;} // ok - occurs in a different class
                {x++;} // ok - occurs in a different class
            };
    }
    {
        j = 200; // ok - assignment
//      j = j + 1; // error - right hand side reads before declaration
//      int k = j = j + 1; // error - right hand side reads before declaration
        int n = j = 300; // ok - j at left hand side of assignment
//      int h = j++; // error - read before declaration
        int l = this.j * 3; // ok - not accessed via simple name
        Object o = new Object(){
                void foo(){j++;} // ok - occurs in a different class
                { j = j + 1;} // ok - occurs in a different class
            };
    }
    int w = x= 3; // ok - x at left hand side of assignment
    int p = x; // ok - instance initializers may access static fields
    static int u = (new Object(){int bar(){return x;}}).bar(); // ok - occurs in a different class
    static int x;
    int m = j = 4; // ok - j at left hand side of assignment
    int o = (new Object(){int bar(){return j;}}).bar(); // ok - occurs in a different class
    int j;
}