Java:The final Keyword

標籤：

 

 1 import java.util.*; 2  3 class Value { 4     int i; 5  6     public Value(int i) { 7         this.i = i; 8     } 9 }10 11 public class FinalData {12 13     private static Random rand = new Random(47);14     private String id;15 16     public FinalData(String id) {17         this.id = id;18     }19     //can be compile-time constants:20     private final int valueOne = 9;21     private static final int VALUE_TWO = 99;22     //Typical public constant:23     public static final int VALUE_THREE = 39;24     //cannot be compile-time constants25     private final int i4 = rand.nextInt(20);26     static final int INT_5 = rand.nextInt(20);27     private Value v1 = new Value(11);28     private final Value v2 = new Value(22);29     private static final Value VAL_3 = new Value(33);30     private final int[] a = { 1, 2, 3, 4, 5, 6 };31 32     public String toString() {33         return id + ": i4 = " + i4 + ", INT_5 = " + INT_5;34     }35 36     public static void main(String[] args) {37         FinalData fd1 = new FinalData("fd1");38         //!fd1.valueOne++; //Error:cannot change value39         fd1.v2.i++;//Object is not constant40         fd1.v1 = new Value(9);//OK--not final41         for (int i = 0; i < fd1.a.length; i++) {42             fd1.a[i]++; //Object is not constant43         }44         //!fd1.v2=new Value(0); //Error:cannot45         //!fd1.VAL_3=new Value(1);//change reference46         //!fd1.a=new int[3];47         System.out.println(fd1);48         System.out.println("creating new FinalData");49         FinalData fd2 = new FinalData("fd2");50         System.out.println(fd1);51         System.out.println(fd2);52     }53 }

輸出

fd1: i4 = 15, INT_5 = 18creating new FinalDatafd1: i4 = 15, INT_5 = 18fd2: i4 = 13, INT_5 = 18

 

Java:The final Keyword