Myths regarding java cloning (Override clone method)

Myths regarding java cloning (Override clone method)

There are lots and lots of good material around us on CLONING. I don’t want to re-write those things here. The purpose of this post is just to clear the confusion that is there among many of us that we need to override clone method.

Public class Person implements Cloneable {

      private int id;

      private String personName;

      // getter setters

      public Person(int id, String name) {

            this.id = id;

            this.personName = name;

      }

      public Object clone() throws CloneNotSupportedException {

            return super.clone();

      }

      //access modifier can be anything like private, default, protected, public

      private Object myClone() throws CloneNotSupportedException {

            return super.clone();

      }

}

Both the methods ‘clone’ and ‘myClone’ will return a clone of person object. E.g.

      Person p = new Person(1,”Manish”);

      Person cloneA = (Person)p.clone();

      Person cloneB = (Person)p.myClone();

Thanks

Manish Kumar Agarwal

Manish.java@outlook.com

Difference between List< ? extends MyParentClass> and List< MyParentClass >

Difference between List< ? extends MyParentClass> and List< MyParentClass >

First look into the following code that is quite self explanatory.

 

  public static void main(String[] args) {

    List<Serializable> serializables = new ArrayList<Serializable>();

    serializables.add(new SomeClass1());

    serializables.add(new SomeClass2());

    process(serializables);

    process2(serializables);//no issues

    List<SomeClass1> SomeClassList = new ArrayList<SomeClass1>();

    SomeClassList.add(new SomeClass1());

    SomeClassList.add(new SomeClass1());

    process(SomeClassList);

    process2(SomeClassList);//compile time error in this line

}

private static void process(List< ? extends Serializable> list){

    Iterator< ? extends Serializable> itr = list.iterator();

    while (itr.hasNext()){

        Serializable s = itr.next();

        System.out.println("process1: " + s.getClass());

    }

}    

private static void process2(List<Serializable> list){

    Iterator<Serializable> itr = list.iterator();

    while (itr.hasNext()){

        Serializable s = itr.next();

        System.out.println("process2: " + s.getClass());

    }

}

public class SomeClass1 implements Serializable {

    private static final long serialVersionUID = 1L;

    private int a;

    private int b;

/*Getters and setters here*/

}

/***Here is my SomeClass2 that I will add it to List***/

import java.io.Serializable;

public class SomeClass2 implements Serializable {

    private static final long serialVersionUID = 1L;

    private String s;

/*Getters and setters here*/

}

Output is

process1: SomeClass1

process1: SomeClass2

process2: SomeClass1

process2: SomeClass2

process1: SomeClass1

process1: SomeClass1

Extract:

• List< MyParentClass> aList;

We can add any object that belongs to MyParentClass or below its hierarchy. But if there is any other List say List, we CAN NOT assign it to aList.

• List< ? extends MyParentClass> bList;

Here if there is any other List say List, we CAN assign it to bList.

Thanks

Manish Kumar Agarwal

Manish.java@outlook.com