deep cloning in java showing null pointer exception

Question

hi im trying to make a simple deep cloning example in java

public class Deepcloning implements Cloneable
{
    public Shallowcloning shallowcopy;
    public Deepcloning() {
    }
    public Shallowcloning getShallowcopy() {
        return shallowcopy;
    }
    public void setShallowcopy(Shallowcloning shallowcopy) {
        this.shallowcopy = shallowcopy;
    }
    public String getEmployee() {
        return employee;
    }
    public void setEmployee(String employee) {
        this.employee = employee;
    }
    private String employee;

    public Object clone() throws CloneNotSupportedException{

        Deepcloning shls=(Deepcloning)super.clone();
        shls.setShallowcopy((Shallowcloning)shallowcopy.clone());
        return shls;
    }
}

and in the main implementation method

public class Clonningimplementation {

    public static void main(String[] args) {

        try {

            Deepcloning dp1 = new Deepcloning();
            dp1.setEmployee("solomon");

            dp1.getShallowcopy().setAge(11);
            dp1.getShallowcopy().setSalary(3000);


            System.out.println("orignal copy employee" + dp1.getEmployee());
            System.out.println("orignal copy employee" + dp1.getShallowcopy().getAge());
            System.out.println("orignal copy employee" + dp1.getShallowcopy().getSalary());
        } catch (ClonenotSupportedException e) {
            e.printstacktrace();
        }

        ...
    }
    ...
}

while running this code im getting null pointer exception. in deep cloning im supposed to clone the reference that too i have done still didnt getting the result any help would be appreciated

You should read this q/a: [Java: recommended solution for deep cloning/copying an instance](http://stackoverflow.com/q/2156120/1065197) — Luiggi Mendoza, Jan 10 '15 at 15:29

score 0 · Accepted Answer · answered Jan 10 '15 at 15:12

dp1.getShallowcopy().setAge(11);

You are directly calling methods on shallowcopy reference without instantiating it. By default it's value is null. calling methods on null reference will give NPE.

You need to do

Deepcloning dp1=new Deepcloning(); dp1.setEmployee("solomon");
dp1.setShallowcopy(new Shallowcloning ());
dp1.getShallowcopy().setAge(11);;
dp1.getShallowcopy().setSalary(3000);

SMA · Answer 2 · 2015-01-10T15:18:00.127

0

By default every object initializes to null and is your shallowcopy.

You are calling getter for shallowcopy as below:

dp1.getShallowcopy().setAge(11);

But you have never setted value for shallowCopy and hence when you call this method it gets evaluated as null.setAge(11); and calling a method on null gives you null pointer exception.

To avoid this, you might need to set Shallowcloning using

Deepcloning dp1=new Deepcloning(); 
dp1.setEmployee("solomon");
dp1.setShallowcopy(...);

This applies to clone method as well.

edited Jan 10 '15 at 15:18

answered Jan 10 '15 at 15:12

SMA

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and whats the solution – user3878073 Jan 10 '15 at 15:15
See the last few lines of my answer. – SMA Jan 10 '15 at 15:20
@user3878073 the solution is: **don't reinvent the wheel**. There are frameworks that help you to do this. – Luiggi Mendoza Jan 10 '15 at 15:28

deep cloning in java showing null pointer exception

2 Answers2