//: c06:FinalData.java // The effect of final on fields. // From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002 // www.BruceEckel.com. See copyright notice in CopyRight.txt. import com.bruceeckel.simpletest.*; import java.util.*; class Value { int i; // Package access public Value(int i) { this.i = i; } } public class FinalData { private static Test monitor = new Test(); private static Random rand = new Random(); private String id; public FinalData(String id) { this.id = id; } // Can be compile-time constants: private final int VAL_ONE = 9; private static final int VAL_TWO = 99; // Typical public constant: public static final int VAL_THREE = 39; // Cannot be compile-time constants: private final int i4 = rand.nextInt(20); static final int i5 = rand.nextInt(20); private Value v1 = new Value(11); private final Value v2 = new Value(22); private static final Value v3 = new Value(33); // Arrays: private final int[] a = { 1, 2, 3, 4, 5, 6 }; public String toString() { return id + ": " + "i4 = " + i4 + ", i5 = " + i5; } public static void main(String[] args) { FinalData fd1 = new FinalData("fd1"); //! fd1.VAL_ONE++; // Error: can't change value fd1.v2.i++; // Object isn't constant! fd1.v1 = new Value(9); // OK -- not final for(int i = 0; i < fd1.a.length; i++) fd1.a[i]++; // Object isn't constant! //! fd1.v2 = new Value(0); // Error: Can't //! fd1.v3 = new Value(1); // change reference //! fd1.a = new int[3]; System.out.println(fd1); System.out.println("Creating new FinalData"); FinalData fd2 = new FinalData("fd2"); System.out.println(fd1); System.out.println(fd2); monitor.expect(new String[] { "%% fd1: i4 = \\d+, i5 = \\d+", "Creating new FinalData", "%% fd1: i4 = \\d+, i5 = \\d+", "%% fd2: i4 = \\d+, i5 = \\d+" }); } } ///:~