The Importance of clone() Method in Java?

Theclone()　The method is used to create a copy of an object of a class that it implementsCloneable　interface. By default, itCopy by field　Because the Object class has no knowledge of the specific class members that are called by this method on an object. Therefore, if the class only has primitive data type members, a new copy of the object will be created, and a reference to the new object copy will be returned. However, if the class contains any class type members, only references to those members' objects will be copied, so the member references in both the original object and the cloned object refer to the same object.

if an attempt is made to clone an object that has not implementedCloneable　interface's class object on which the method is calledclone()method, then you will getCloneNotSupportedException　. This interface ismarked interface,and that thisinterfaceThe implementation simply indicates that it can be called on objects of the implementing classObject.clone()method.

syntax

protected Object clone() throws CloneNotSupportedException

We can useclone()Two ways to implement this method

Shallow Copy

If the class also has non-primitive data type members, then this isObject.clone()The result of the default cloning functionality provided by the method. In the case of 'shallow copy', the cloned object still refers to the same object as the original object, because only object references are copied, not the objects themselves.

Example

public class ShallowCopyTest {
　　　public static void main(String args[]) {
　　　　　　A a1　= new A();
　　　　　　A a2　= (A) a1.clone();
　　　　　　a1.sb.append("w3codebox!");
　　　　　　System.out.println(a1);
　　　　　　System.out.println(a2);
　　　}
}
class A implements Cloneable {
　　　public StringBuffer sb = new StringBuffer("Welcome to ");
　　　　　　public String toString() {
　　　　　　　　　return sb.toString();
　　　　　　}
　　　public Object clone() {
　　　　　　try {
　　　　　　　　　return super.clone();
　　　　　　} catch(CloneNotSupportedException e) {
　　　　　　}
　　　　　　return　null;
　　　}
}

Output Result

Welcome　to　w3codebox!
Welcome　to　w3codebox!

Deep Copy

For classes with non-primitive type members, we need to overrideclone()　methods to implementDeep Copy,because it also needs to clone member objects, and the default cloning mechanism cannot do this.

Example

public class DeepCopyTest {
　　　public static void main(String args[]) {
　　　　　　A a1　= new A();
　　　　　　A a2　= (A) a1.clone();
　　　　　　a1.sb.append("　w3codebox!");
　　　　　　System.out.println(a1);
　　　　　　System.out.println(a2);
　　　}
}
class A implements Cloneable {
　　　public StringBuffer sb = new StringBuffer("Welcome to ");
　　　public String toString() {
　　　　　　return sb.toString();
　　　}
　　　public Object clone() {
　　　　　　try {
　　　　　　　　　A a = (A) super.clone();
　　　　　　　　　a.sb = new StringBuffer(sb.toString());
　　　　　　　　　return a;
　　　　　　}
　　　　　　catch(CloneNotSupportedException e) {
　　　　　　}
　　　　　　return　null;
　　　}
}

Output Result

Welcome　to　w3codebox!
Welcome　to