物件的克隆
摘要：
物件的克隆
物件地址的引用：
public class Person {
int id;
String name;
public Person(int id, String name) {
this.id = id;
...
物件的克隆
物件地址的引用：
public class Person {
int id;
String name;
public Person(int id, String name) {
this.id = id;
this.name = name;
}
@Override
public String toString() {
return "編號："+ this.id+" 姓名："+ this.name;
}
}
public class Demo {
public static void main(String[] args) throws Exception {
Person p1 = new Person(123,"hcx");
Person p2 = p1;
System.out.println("p1:"+p1);//p1:編號：123 姓名：hcx
System.out.println("p2:"+ p2);//p2:編號：123 姓名：hcx
}
}
以上屬於物件地址的引用：
物件地址的引用.png
一、物件的淺克隆
Person:
class Address{
String city;
public Address(String city){
this.city = city;
}
}
public class Person implements Cloneable{
int id;
String name;
Address address;
public Person(int id, String name) {
this.id = id;
this.name = name;
}
public Person(int id, String name, Address address) {
this.id = id;
this.name = name;
this.address = address;
System.out.println("=======構造方法呼叫了===");
}
@Override
public String toString() {
return "編號："+ this.id+" 姓名："+ this.name+" 地址："+ address.city;
}
@Override
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
Demo：
public class Demo {
public static void main(String[] args) throws Exception {
Address address = new Address("深圳");
Person p1 = new Person(123,"hcx",address);
Person p2 = (Person) p1.clone(); //clone() 克隆了一個物件。
p2.name = "gia";
p2.address.city ="廣州";
System.out.println("p1:"+p1);
System.out.println("p2:"+ p2);
System.out.println("p1:"+p1);//p1:編號：123 姓名：hcx 地址：廣州
System.out.println("p2:"+ p2);//p2:編號：123 姓名：gia 地址：廣州
}
}
物件的淺克隆.png
物件淺克隆要注意的細節：
- 如果一個物件需要呼叫clone的方法克隆，那麼該物件所屬的類必須要實現Cloneable介面。
- Cloneable介面是一個標識介面而已，沒有任何方法。
- 物件的淺克隆就是克隆一個物件的時候，如果被克隆的物件中維護了另外一個類的物件，這時候只是克隆另外一個物件的地址，而沒有把另外一個物件也克隆一份。
- 物件的淺克隆不會呼叫到構造方法的。
二、物件的深克隆
物件的深克隆：利用物件的輸入輸出流把物件先寫到檔案上，然後再讀取物件的資訊。這個過程就稱作為物件的深克隆。
Person：
import java.io.Serializable;
class Address implements Serializable{
String city;
public Address(String city){
this.city = city;
}
}
public class Person implements Cloneable,Serializable {
int id;
String name;
Address address;
public Person(int id, String name) {
this.id = id;
this.name = name;
}
public Person(int id, String name, Address address) {
this.id = id;
this.name = name;
this.address = address;
System.out.println("=======構造方法呼叫了===");
}
@Override
public String toString() {
return "編號："+ this.id+" 姓名："+ this.name+" 地址："+ address.city;
}
@Override
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
Demo2:
public class Demo2 {
public static void main(String[] args) throws IOException, ClassNotFoundException {
Address address = new Address("深圳");
Person p1 = new Person(123,"hcx",address);
writeObj(p1);
Person p2=readObj();
p2.address.city = "廣州";
System.out.println("p1:"+ p1);//p1:編號：123 姓名：hcx 地址：深圳
System.out.println("p2:"+ p2);//p1:編號：123 姓名：hcx 地址：廣州
}
//再從檔案中讀取物件的資訊
public static Person readObj() throws ClassNotFoundException, IOException{
FileInputStream fileInputStream = new FileInputStream("F:\\obj.txt");
//建立物件的輸入流物件
ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
return (Person) objectInputStream.readObject();
}
//先要把物件寫到檔案上。
public static void writeObj(Person p) throws IOException{
//建立一個檔案 的輸出流物件
FileOutputStream fileOutputStream= new FileOutputStream("F:\\obj.txt");
//建立物件的輸出流
ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
//把物件寫出
objectOutputStream.writeObject(p);
//關閉資源
objectOutputStream.close();
}
}