無論是在java面試過程中,還是在與各種老鳥交流的過程中,對java對象的深淺拷貝,都是一個繞不開的問題,這個問題看似很容易,卻是大多數(shù)人用來區(qū)分小白的標準問題。現(xiàn)在對該問題進行說明。
1.定義
淺克隆(拷貝):復(fù)制一個對象的實例,但是這個對象中包含的其它的對象還是共用的。一般用super.clone()方法,clone的對象就是淺克隆。
深克隆(拷貝):復(fù)制一個對象的實例,而且這個對象中包含的其它的對象也要復(fù)制一份。如果使用clone(),那么需要對clone方法進行重寫,復(fù)制一個對象super.clone(),之后再一一對屬性進行復(fù)制。這樣顯得非常冗余,幸好,在java中還可以通過流來實現(xiàn)。但是注意,對象需要實現(xiàn)Serializable接口。
2.舉例
有如下類Husband, Husband又引用了Wife。
類結(jié)構(gòu)圖
Wife類
package com.dhb.CloneTest;
import lombok.Data;
import java.io.Serializable;
import java.util.Date;
@Data
public class Wife implements Serializable {
private String name;
private Date birthday;
public Wife() {
this.name = "思思";
this.birthday = new Date();
}
public Wife(String name, Date birthday) {
this.name = name;
this.birthday = birthday;
}
}
Husband類
package com.dhb.CloneTest;
import lombok.Data;
import java.io.*;
import java.util.Date;
@Data
public class Husband implements Cloneable,Serializable {
private Wife wife;
private Date birthday;
public Husband() {
this.wife = new Wife();
this.birthday = new Date();
}
public Husband(Wife wife, Date birthday) {
this.wife = wife;
this.birthday = birthday;
}
public Object clone() {
Husband husband = null;
try {
husband = (Husband) super.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}finally {
return husband;
}
}
public Object deepClone() throws IOException, ClassNotFoundException {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(this);
ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
ObjectInputStream ois = new ObjectInputStream(bis);
return ois.readObject();
}
}
在Husband類中存在clone和deepClone方法。現(xiàn)在對這兩個方法進行測試。
package com.dhb.CloneTest;
import java.io.IOException;
public class CloneTest {
public static void main(String[] args) {
try {
Husband husband = new Husband();
System.out.println("husband birthday is :"+husband.getBirthday());
System.out.println("wife birthday is :"+husband.getWife().getBirthday());
System.out.println("***********************************************");
Husband husband1 = (Husband) husband.clone();
System.out.println("husband1 birthday is :"+husband1.getBirthday());
System.out.println("wife birthday is :"+husband1.getWife().getBirthday());
System.out.println("***********************************************");
System.out.println("husband 是否相同:"+(husband == husband1));
System.out.println("wife 是否相同:"+(husband.getWife() == husband1.getWife()));
System.out.println("***********************************************");
Husband husband2 = (Husband) husband.deepClone();
System.out.println("husband2 birthday is :"+husband2.getBirthday());
System.out.println("wife birthday is :"+husband2.getWife().getBirthday());
System.out.println("***********************************************");
System.out.println("husband 是否相同:"+(husband == husband2));
System.out.println("wife 是否相同:"+(husband.getWife() == husband2.getWife()));
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
運行結(jié)果:
husband birthday is :Mon Aug 07 19:03:38 CST 2017
wife birthday is :Mon Aug 07 19:03:38 CST 2017
***********************************************
husband1 birthday is :Mon Aug 07 19:03:38 CST 2017
wife birthday is :Mon Aug 07 19:03:38 CST 2017
***********************************************
husband 是否相同:false
wife 是否相同:true
***********************************************
husband2 birthday is :Mon Aug 07 19:03:38 CST 2017
wife birthday is :Mon Aug 07 19:03:38 CST 2017
***********************************************
husband 是否相同:false
wife 是否相同:false
注:上述代碼中的@Data 是lombak的一個注解。
當(dāng)然,實現(xiàn)深克隆的方法并不局限于流這一種辦法,還可以通過json等其他辦法實現(xiàn)。