57 lines
1.8 KiB
Java
57 lines
1.8 KiB
Java
// reuse/FinalData.java
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// (c)2016 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://mindviewinc.com/Books/OnJava/ for more book information.
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// The effect of final on fields.
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import java.util.*;
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class Value {
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int i; // Package access
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public Value(int i) { this.i = i; }
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}
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public class FinalData {
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private static Random rand = new Random(47);
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private String id;
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public FinalData(String id) { this.id = id; }
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// Can be compile-time constants:
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private final int valueOne = 9;
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private static final int VALUE_TWO = 99;
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// Typical public constant:
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public static final int VALUE_THREE = 39;
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// Cannot be compile-time constants:
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private final int i4 = rand.nextInt(20);
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static final int INT_5 = rand.nextInt(20);
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private Value v1 = new Value(11);
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private final Value v2 = new Value(22);
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private static final Value VAL_3 = new Value(33);
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// Arrays:
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private final int[] a = { 1, 2, 3, 4, 5, 6 };
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@Override
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public String toString() {
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return id + ": " + "i4 = " + i4 + ", INT_5 = " + INT_5;
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}
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public static void main(String[] args) {
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FinalData fd1 = new FinalData("fd1");
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//! fd1.valueOne++; // Error: can't change value
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fd1.v2.i++; // Object isn't constant!
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fd1.v1 = new Value(9); // OK -- not final
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for(int i = 0; i < fd1.a.length; i++)
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fd1.a[i]++; // Object isn't constant!
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//! fd1.v2 = new Value(0); // Error: Can't
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//! fd1.VAL_3 = new Value(1); // change reference
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//! fd1.a = new int[3];
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System.out.println(fd1);
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System.out.println("Creating new FinalData");
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FinalData fd2 = new FinalData("fd2");
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System.out.println(fd1);
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System.out.println(fd2);
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}
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}
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/* Output:
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fd1: i4 = 15, INT_5 = 18
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Creating new FinalData
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fd1: i4 = 15, INT_5 = 18
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fd2: i4 = 13, INT_5 = 18
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*/
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