Java/Class/This

Calling constructors with this

// : 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();
  }
} ///:~

Simple use of the this keyword

// : 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();
  }
} ///:~

This shows off the uses of this

/*
 * 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());
  }
}