Java clone example 2018-03-26 23:26
We can use clone method to clone an object. This is a native method in Object (make it faster). If you want to use this method you need to implement cloneable interface. If you want to use this method in different package do not forget change this method to be public. The example code is here.
public class Address implements Cloneable {
private String country;
private String city;
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
@Override
public String toString() {
return "Address{" +
"country='" + country + '\'' +
", city='" + city + '\'' +
'}';
}
@Override
public Address clone() throws CloneNotSupportedException {
return (Address) super.clone();
}
}
public class User implements Cloneable {
private String name;
private int age;
private Address address;
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public User clone() throws CloneNotSupportedException {
return (User) super.clone();
}
@Override
public String toString() {
return "User{" +
"name='" + name + '\'' +
", age=" + age +
", address=" + address +
'}';
}
}
public class DeepCopyUser implements Cloneable {
private String name;
private int age;
private Address address;
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public DeepCopyUser clone() throws CloneNotSupportedException {
DeepCopyUser copyUser = (DeepCopyUser) super.clone();
copyUser.setAddress(address.clone());
return copyUser;
}
@Override
public String toString() {
return "User{" +
"name='" + name + '\'' +
", age=" + age +
", address=" + address +
'}';
}
}
public class CloneClient {
public static void main(String[] args) throws CloneNotSupportedException {
System.out.println("-------use copy-------");
testCopy();
System.out.println("-------use deep copy-------");
testDeepCopy();
}
private static void testCopy() throws CloneNotSupportedException {
Address beijing = new Address();
beijing.setCountry("China");
beijing.setCity("beijing");
User henry = new User();
henry.setName("Henry");
henry.setAge(30);
henry.setAddress(beijing);
User cloneHenry = henry.clone();
System.out.println("Henry:" + henry);
System.out.println("Henry copy:" + cloneHenry);
System.out.println("change Henry's address");
Address newAddress = henry.getAddress();
newAddress.setCountry("USA");
newAddress.setCity("San Francisco");
System.out.println("Henry:" + henry);
System.out.println("Henry copy:" + cloneHenry);
}
private static void testDeepCopy() throws CloneNotSupportedException {
Address beijing = new Address();
beijing.setCountry("China");
beijing.setCity("beijing");
DeepCopyUser henry = new DeepCopyUser();
henry.setName("Henry");
henry.setAge(30);
henry.setAddress(beijing);
DeepCopyUser cloneHenry = henry.clone();
System.out.println("Henry:" + henry);
System.out.println("Henry copy:" + cloneHenry);
System.out.println("change Henry's address");
Address newAddress = henry.getAddress();
newAddress.setCountry("USA");
newAddress.setCity("San Francisco");
System.out.println("Henry:" + henry);
System.out.println("Henry copy:" + cloneHenry);
}
}
The output is here.
-------use copy-------
Henry:User{name='Henry', age=30, address=Address{country='China', city='beijing'}}
Henry copy:User{name='Henry', age=30, address=Address{country='China', city='beijing'}}
change Henry's address
Henry:User{name='Henry', age=30, address=Address{country='USA', city='San Francisco'}}
Henry copy:User{name='Henry', age=30, address=Address{country='USA', city='San Francisco'}}
-------use deep copy-------
Henry:User{name='Henry', age=30, address=Address{country='China', city='beijing'}}
Henry copy:User{name='Henry', age=30, address=Address{country='China', city='beijing'}}
change Henry's address
Henry:User{name='Henry', age=30, address=Address{country='USA', city='San Francisco'}}
Henry copy:User{name='Henry', age=30, address=Address{country='China', city='beijing'}}
clone method works well for primitive type(int, boolean, etc.). String is not primitive type but it is immutable. Both of them are OK. If you want to copy reference types like Address. We should use Deep Copy to avoid original and cloned class using the same reference.
EOF