The effect of final on fields : final « Class Definition « Java Tutorial

1. Java Tutorial
2. Class Definition
3. final

import java.util.Random;

class A {
  int i; // Package access

  public A(int i) {
    this.i = i;
  }
}

public class MainClass {
  private static Random rand = new Random();

  private String id;

  public MainClass(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 A v1 = new A(11);

  private final A v2 = new A(22);

  private static final A v3 = new A(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) {
    MainClass fd1 = new MainClass("fd1");
    fd1.v2.i++; 
    fd1.v1 = new A(9); 
    for (int i = 0; i < fd1.a.length; i++)
      fd1.a[i]++; 

    System.out.println(fd1);
    System.out.println("Creating new FinalData");
    MainClass fd2 = new MainClass("fd2");
    System.out.println(fd1);
    System.out.println(fd2);
  }
}

fd1: i4 = 15, i5 = 5
Creating new FinalData
fd1: i4 = 15, i5 = 5
fd2: i4 = 15, i5 = 5