在未实现Cloneable接口的对象上调用clone（）方法时，不会引发CloneNotSupportedException

Question

I recently started Java programming and according to Java SE API Documentation, the Cloneable interface is implemented to indicate that clone operations on that class are allowed. If not, then a CloneNotSupportedException is thrown. However in a practice session i managed to run a program that cloned a class that does not implement the Cloneable interface and no exception was thrown. I need to know why the exception was not thrown. I am using JDK 6 update 45 and latest Eclipse IDE on Windows 7. The following is the code:

package com.warren.project.first;

public class PracticeClass {

   //explicit initialisation of PracticeClass Instance Variables
   private int fieldOne=1;
   private int fieldTwo=2;
   private int fieldThree=3;

   //setters and getters for instance fields of PracticeClass
   public void setField1(int field1){
     this.fieldOne=field1;
   }

   public void setField2(int field2){
     this.fieldTwo=field2;
   }

   public void setField3(int field3){
     this.fieldThree=field3;
   }

   public int getField1(){
     return this.fieldOne;
   }

   public int getField2(){
     return this.fieldTwo;
   }

   public int getField3(){
     return this.fieldThree;
   }


   //This method clones the PracticeClass's instances and returns the clone
   @Override
   public PracticeClass clone(){
      PracticeClass practiceClass= this;
      return practiceClass;
   }

}


package com.warren.project.first;

public class AppMain {

  public static void main(String[] args) {      
    //Create PracticeClass Object
    PracticeClass pc1=new PracticeClass();

    //Set its instance fields using setters
    pc1.setField1(111);
    pc1.setField2(222);
    pc1.setField3(333);

    //Display Values to screen
    System.out.println(pc1.getField1()+" "+pc1.getField2()+" "+pc1.getField3());

    //Create clone of PracticeClass object
    PracticeClass pc2=pc1.clone();

    //Print values from PracticeClass clone object
    System.out.println(pc2.getField1()+" "+pc2.getField2()+" "+pc2.getField3());
  }

}

This code executes successfully without any exception thrown. Why isn't the CloneNotSupportedException thrown?

Answer 1

In order for CloneNotSupportedException to be thrown, you must call super.clone() inside your own clone() method. This method will verify if your class implements Cloneable