immutable1.java

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//: appendixa:Immutable1.java
// Objects that cannot be modified are immune to aliasing.
// From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
import com.bruceeckel.simpletest.*;

public class Immutable1 {
  private static Test monitor = new Test();
  private int data;
  public Immutable1(int initVal) {
    data = initVal;
  }
  public int read() { return data; }
  public boolean nonzero() { return data != 0; }
  public Immutable1 multiply(int multiplier) {
    return new Immutable1(data * multiplier);
  }
  public static void f(Immutable1 i1) {
    Immutable1 quad = i1.multiply(4);
    System.out.println("i1 = " + i1.read());
    System.out.println("quad = " + quad.read());
  }
  public static void main(String[] args) {
    Immutable1 x = new Immutable1(47);
    System.out.println("x = " + x.read());
    f(x);
    System.out.println("x = " + x.read());
    monitor.expect(new String[] {
      "x = 47",
      "i1 = 47",
      "quad = 188",
      "x = 47"
    });
  }
} ///:~