When you declare a variable final, you do not want anyone to change it. If the type of variable is primitive types, you can undoubtedly make it. Unfortunately, if the variable is a reference to an object, the "final" stuff you think may be not final!
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Non-compliant Code Example
| Code Block |
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class Test{
Â
 Test(int a, int b){
  this.a = a;
  this.b = b;
 }
 void set_ab(int a, int b){
  this.a = a;
  this.b = b;
 }
 void print_ab(){
  System.out.println("the value a is: "+this.a);
  System.out.println("the value b is: "+this.b);
 }
 private int a;
 private int b;
}
public class TestFinal1 {
Â
 public static void main(String[] args) {
       final Test mytest = new Test(1,2);
       mytest.print_ab();
       //now we change the value of a,b.
       mytest.set_ab(5, 6);
       mytest.print_ab();
      Â
   }
}
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We can see that the value of a and b has been changed, which means that when you declare a reference final, it only means that the reference can not be changed but the contents it refer to can still be changed!
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Non-Compliant Solution
If you do not want to change a and b after they are initialized, the simplest approach is to declare a and b final:
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But now you can not have setter method of a and b.
Compliant Solution
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An alternative approach is to provide the clone method in the class. When you want do something about the object, you can use clone method to get a copy of original object. Now, you can do everything to this new object, and the original one will be never changed.
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