在开发过程中，创建多个数据相同的对象，每次new都开销比较大，在这里可以使用对象克隆，以先创建的原型对象为模板进行对象的复制。这种模式是实现了一个原型接口，该接口用于创建当前对象的克隆。当直接创建对象的代价比较大时，则采用这种模式。例如，一个对象需要在一个高代价的数据库操作之后被创建。我们可以缓存该对象，在下一个请求时返回它的克隆，在需要的时候更新数据库，以此来减少数据库调用
浅克隆
在浅克隆中，如果原型对象的成员变量是值类型，将复制一份给克隆对象；如果原型对象的成员变量是引用类型，则将引用对象的地址复制一份给克隆对象，也就是说原型对象和克隆对象的成员变量指向相同的内存地址
java
public class Person implements Cloneable{
int num;
String name;
public Person() {
}
public Person(int num, String name) {
this.num = num;
this.name = name;
}
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
protected Person clone() throws CloneNotSupportedException {
Person person = (Person)super.clone();
return person;
}
@Override
public String toString() {
return "Person{" +
"num=" + num +
", name='" + name + '\'' +
'}';
}
}
java
public class Test {
public static void main(String[] args) throws CloneNotSupportedException {
Person p1 = new Person(100,"jim");
Person p2 =p1.clone();//clone方法 返回一个新对象
p2.name = "tom";
System.out.println(p1);//100 ,jim
System.out.println(p2);//100 tom
System.out.println(p1==p2);//false
}
}深克隆
多层克隆
在深克隆中，无论原型对象的成员变量是值类型还是引用类型，都将复制一份给克隆对象，深克隆将原型对象的所有引用对象也复制一份给克隆对象。简单来说，在深克隆中，除了对象本身被复制外，对象所包含的所有成员变量也将复制
java
public class Person implements Cloneable{
int num;
String name;
Address address;
public Person() {
}
public Person(int num, String name) {
this.num = num;
this.name = name;
}
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
@Override
protected Person clone() throws CloneNotSupportedException {
Person person = (Person)super.clone();
person.address = address.clone(); //深度复制 联同person中关联的对象也一同克隆.
return person;
}
@Override
public String toString() {
return "Person{" +
"num=" + num +
", name='" + name + '\'' +
", address=" + address +
'}';
}
}
java
public class Address implements Cloneable{
String address;
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public String toString() {
return "Address{" +
"address='" + address + '\'' +
'}';
}
@Override
protected Address clone() throws CloneNotSupportedException {
return (Address) super.clone();
}
}序列化
java
public class Address implements Serializable {
String address;
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
@Override
public String toString() {
return "Address{" +
"address='" + address + '\'' +
'}';
}
}
java
public class Person implements Serializable {
int num;
String name;
Address address;
public Person() {
}
public Person(int num, String name) {
this.num = num;
this.name = name;
}
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
/**
* 自定义克隆方法
* @return
*/
public Person myclone() {
Person person = null;
try { // 将该对象序列化成流,因为写在流里的是对象的一个拷贝，而原对象仍然存在于JVM里面。所以利用这个特性可以实现对象的深拷贝
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(this);
// 将流序列化成对象
ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
ObjectInputStream ois = new ObjectInputStream(bais);
person = (Person) ois.readObject();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
return person;
}
@Override
public String toString() {
return "Person{" +
"num=" + num +
", name='" + name + '\'' +
", address=" + address +
'}';
}
}练习
java
import java.util.Scanner;
public class Main {
public static void main(String[] args) throws CloneNotSupportedException {
Scanner scanner = new Scanner(System.in);
int num = scanner.nextInt();
while(num-->0){
String color = scanner.next();
int width = scanner.nextInt();
int height = scanner.nextInt();
Prototype prototype = new Prototype(color, width, height);
Prototype clone = prototype.clone();
System.out.println(clone.toString());
}
}
}
class Prototype implements Cloneable{
private String color;
private int width;
private int height;
public Prototype(String color, int width, int height) {
this.color = color;
this.width = width;
this.height = height;
}
@Override
public String toString() {
return "Color: " + color + ", Width: " + width + ", Height: " + height;
}
@Override
protected Prototype clone() throws CloneNotSupportedException {
return (Prototype) super.clone();
}
}