Java/Class/This

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());
 }

}

      </source>