Java/Class/This
Версия от 21:01, 31 мая 2010; (обсуждение)
Calling constructors with this
<source lang="java">
// : c04:Flower.java // Calling constructors with "this." // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. public class Flower {
int petalCount = 0; String s = new String("null"); Flower(int petals) { petalCount = petals; System.out.println("Constructor w/ int arg only, petalCount= " + petalCount); } Flower(String ss) { System.out.println("Constructor w/ String arg only, s=" + ss); s = ss; } Flower(String s, int petals) { this(petals); //! this(s); // Can"t call two! this.s = s; // Another use of "this" System.out.println("String & int args"); } Flower() { this("hi", 47); System.out.println("default constructor (no args)"); } void print() { //! this(11); // Not inside non-constructor! System.out.println("petalCount = " + petalCount + " s = " + s); } public static void main(String[] args) { Flower x = new Flower(); x.print(); }
} ///:~
</source>
Simple use of the this keyword
<source lang="java">
// : c04:Leaf.java // Simple use of the "this" keyword. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. public class Leaf {
int i = 0; Leaf increment() { i++; return this; } void print() { System.out.println("i = " + i); } public static void main(String[] args) { Leaf x = new Leaf(); x.increment().increment().increment().print(); }
} ///:~
</source>
This shows off the uses of this
<source lang="java">
/*
* Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002. * All rights reserved. Software written by Ian F. Darwin and others. * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $ * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS"" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s, * pioneering role in inventing and promulgating (and standardizing) the Java * language and environment is gratefully acknowledged. * * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for * inventing predecessor languages C and C++ is also gratefully acknowledged. */
// This shows off the uses of "this". It is a non-public class // just so the file name UseThis doesn"t have to be the class name // (some students found "This" in the class name confusing in this example). public class MyClass {
final static int MAXX=640, MAXY=480; // low-res (VGA) int x, y; // current location /** Construct a MyClass with x and y values */ MyClass(int x, int y) { this.x = x; this.y = y; } /** Construct a MyClass with default values */ MyClass() { this(MAXX/2, MAXY/2); // Use the constructor above } public String toString() { return "[" + x + "," + y + "]"; } /** Test main program */ public static void main(String[] av) { System.out.println(new MyClass(300,100)); System.out.println(new MyClass()); }
}
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