How do I copy an object in Java?

How to Copy an Object in Java? 📝🚀

Copying objects in Java can be a tricky task, especially when you want to create a fresh copy without affecting the original object. In this blog post, we'll explore a common issue and provide you with easy solutions to copy objects in Java. 🚀

Understanding the Problem

Consider the following code snippet:

DummyBean dum = new DummyBean();
dum.setDummy("foo");
System.out.println(dum.getDummy()); // prints 'foo'

DummyBean dumtwo = dum;
System.out.println(dumtwo.getDummy()); // prints 'foo'

dum.setDummy("bar");
System.out.println(dumtwo.getDummy()); // prints 'bar' but it should print 'foo'

In this example, we have an object dum of type DummyBean and we want to create a fresh copy of it and assign it to dumtwo. However, when we change something in dum, the same change is reflected in dumtwo as well. 😱

Why does this happen?

The issue here is that Java copies the reference of the object when we assign it to another variable. So, both dum and dumtwo point to the same memory location, leading to unexpected behavior when modifying one of them. 😮

Solution 1: Use the Copy Constructor

One way to achieve object copying without affecting the original object is by using a copy constructor. By implementing a copy constructor in the DummyBean class, we can create a fresh copy of the object. Here's how you can do it:

public class DummyBean {
    private String dummy;

    public DummyBean() {
        // default constructor
    }

    public DummyBean(DummyBean other) {
        this.dummy = other.dummy;
    }

    // getters and setters...
}

Now, let's modify the code to utilize the copy constructor:

DummyBean dum = new DummyBean();
dum.setDummy("foo");
System.out.println(dum.getDummy()); // prints 'foo'

DummyBean dumtwo = new DummyBean(dum);
System.out.println(dumtwo.getDummy()); // prints 'foo'

dum.setDummy("bar");
System.out.println(dumtwo.getDummy()); // prints 'foo' (Yay! 🎉)

With the copy constructor, we are creating a new instance of DummyBean using the values from the original object. This way, any modifications to dum will not affect dumtwo.

Solution 2: Use Object Cloning

Another way to achieve object copying is by using the clone() method in Java. However, this method comes with its own set of caveats and complexities. Nonetheless, let's explore how to copy objects using cloning:

1. Implement the Cloneable interface in the DummyBean class:

   public class DummyBean implements Cloneable { // class definition... }

2. Override the clone() method:

   @Override public Object clone() throws CloneNotSupportedException { return super.clone(); }

3. Modify the code to utilize object cloning:

   DummyBean dum = new DummyBean(); dum.setDummy("foo"); System.out.println(dum.getDummy()); // prints 'foo' DummyBean dumtwo = (DummyBean) dum.clone(); System.out.println(dumtwo.getDummy()); // prints 'foo' dum.setDummy("bar"); System.out.println(dumtwo.getDummy()); // prints 'foo' (Wohoo! 🎉)

By calling the clone() method on dum, we create a separate copy of the object, allowing independent modifications on dum and dumtwo.

Conclusion

Copying objects in Java can be a challenge, but with the right techniques, it becomes much simpler. In this blog post, we explored two solutions: using a copy constructor and utilizing object cloning. Choose the approach that best suits your needs.

Now, go ahead and copy those objects without any worries! 👯‍♂️

Have you encountered any other methods to copy objects in Java? Share your thoughts and experiences in the comments below. Let's learn from each other! 💬😊