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FinalData.javaAPI DocExample3711Mon Apr 06 18:10:24 BST 1998None

FinalData.java

//: FinalData.java
//////////////////////////////////////////////////
// Copyright (c) Bruce Eckel, 1998
// Source code file from the book "Thinking in Java"
// All rights reserved EXCEPT as allowed by the
// following statements: You can freely use this file
// for your own work (personal or commercial),
// including modifications and distribution in
// executable form only. Permission is granted to use
// this file in classroom situations, including its
// use in presentation materials, as long as the book
// "Thinking in Java" is cited as the source. 
// Except in classroom situations, you cannot copy
// and distribute this code; instead, the sole
// distribution point is http://www.BruceEckel.com 
// (and official mirror sites) where it is
// freely available. You cannot remove this
// copyright and notice. You cannot distribute
// modified versions of the source code in this
// package. You cannot use this file in printed
// media without the express permission of the
// author. Bruce Eckel makes no representation about
// the suitability of this software for any purpose.
// It is provided "as is" without express or implied
// warranty of any kind, including any implied
// warranty of merchantability, fitness for a
// particular purpose or non-infringement. The entire
// risk as to the quality and performance of the
// software is with you. Bruce Eckel and the
// publisher shall not be liable for any damages
// suffered by you or any third party as a result of
// using or distributing software. In no event will
// Bruce Eckel or the publisher be liable for any
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// indirect, special, consequential, incidental, or
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// the theory of liability, arising out of the use of
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// possibility of such damages. Should the software
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// necessary servicing, repair, or correction. If you
// think you've found an error, please email all
// modified files with clearly commented changes to:
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// address for non-code errors found in the book.)
/////////////////////////////////////////////////

// The effect of final on fields

class Value {
  int i = 1;
}

public class FinalData {
  // Can be compile-time constants
  final int i1 = 9;
  static final int I2 = 99;
  // Typical public constant:
  public static final int I3 = 39;
  // Cannot be compile-time constants:
  final int i4 = (int)(Math.random()*20);
  static final int i5 = (int)(Math.random()*20);
  
  Value v1 = new Value();
  final Value v2 = new Value();
  static final Value v3 = new Value();
  //! final Value v4; // Pre-Java 1.1 Error: 
                      // no initializer
  // Arrays:
  final int[] a = { 1, 2, 3, 4, 5, 6 };

  public void print(String id) {
    System.out.println(
      id + ": " + "i4 = " + i4 + 
      ", i5 = " + i5);
  }
  public static void main(String[] args) {
    FinalData fd1 = new FinalData();
    //! fd1.i1++; // Error: can't change value
    fd1.v2.i++; // Object isn't constant!
    fd1.v1 = new Value(); // OK -- not final
    for(int i = 0; i < fd1.a.length; i++)
      fd1.a[i]++; // Object isn't constant!
    //! fd1.v2 = new Value(); // Error: Can't 
    //! fd1.v3 = new Value(); // change handle
    //! fd1.a = new int[3];

    fd1.print("fd1");
    System.out.println("Creating new FinalData");
    FinalData fd2 = new FinalData();
    fd1.print("fd1");
    fd2.print("fd2");
  }
} ///:~