Java集合引用传递问题（集合的浅复制和深复制）
2018-01-09 19:32
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浅复制
实体类
package com.ahut.entity;
import java.io.Serializable;
import java.util.Date;
/**
*
* @ClassName: Demo
* @Description:
* @author cheng
* @date 2017年11月21日 下午8:32:59
*/
public class Demo implements Serializable {
/**
* 序列化
*/
private static final long serialVersionUID = 4122974131420281791L;
private String id;
private String userName;
private int age;
private Date birthDay;
public Demo() {
super();
// TODO Auto-generated constructor stub
}
@Override
public String toString() {
return "Demo [birthDay=" + birthDay + ", userName=" + userName + ", age=" + age + ", id=" + id + "]";
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Date getBirthDay() {
return birthDay;
}
public void setBirthDay(Date birthDay) {
this.birthDay = birthDay;
}
}集合测试
/**
*
* @Title: testCollection
* @Description:
*/
@Test
public void testCollection(){
// 创建元素1
Demo demo1 = new Demo();
demo1.setId("1234");
demo1.setUserName("demo1");
demo1.setAge(20);
demo1.setBirthDay(new Date());
// 创建元素2
Demo demo2 = new Demo();
demo2.setId("5678");
demo2.setUserName("demo2");
demo2.setAge(40);
demo2.setBirthDay(new Date());
// 将元素添加到list1中
List<Demo> demoList1 = new ArrayList<>();
demoList1.add(demo1);
demoList1.add(demo2);
// 使用list1作为参数，创建list2
List<Demo> demoList2 = new ArrayList<>(demoList1);
System.out.println("demoList1====================================");
for(Demo demo : demoList1){
System.out.println(demo);
}
System.out.println("demoList2====================================");
for(Demo demo : demoList2){
System.out.println(demo);
}
输出如下：
demoList1====================================
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo1, age=20, id=1234]
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo2, age=40, id=5678]
demoList2====================================
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo1, age=20, id=1234]
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo2, age=40, id=5678]
// 取出list2中的元素并修改其属性，发现list1中的元素也发生了改变
Demo demo3 = demoList2.get(0);
demo3.setAge(9999);
System.out.println("demoList1====================================");
for(Demo demo : demoList1){
System.out.println(demo);
}
System.out.println("demoList2====================================");
for(Demo demo : demoList2){
System.out.println(demo);
}
输出如下：
demoList1====================================
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo1, age=9999, id=1234]
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo2, age=40, id=5678]
demoList2====================================
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo1, age=<
11e0a
span class="hljs-number">9999, id=1234]
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo2, age=40, id=5678]
// 删除list2中的元素，list1不发生改变
demoList2.remove(0);
System.out.println("demoList1====================================");
for(Demo demo : demoList1){
System.out.println(demo);
}
System.out.println("demoList2====================================");
for(Demo demo : demoList2){
System.out.println(demo);
}
输出结果：
demoList1====================================
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo1, age=9999, id=1234]
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo2, age=40, id=5678]
demoList2====================================
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo2, age=40, id=5678]
// 取出list2中剩下的元素并修改其属性，发现list1中的元素也发生了改变
Demo demo4 = demoList2.get(0);
demo4.setAge(6666);
System.out.println("demoList1====================================");
for(Demo demo : demoList1){
System.out.println(demo);
}
System.out.println("demoList2====================================");
for(Demo demo : demoList2){
System.out.println(demo);
}
输出结果：
demoList1====================================
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo1, age=9999, id=1234]
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo2, age=6666, id=5678]
demoList2====================================
Demo [birthDay=Tue Jan 09 14:29:21 CST 2018, userName=demo2, age=6666, id=5678]
}内存分析
拷贝list中的对象是一致的，而list是2个对象
改变其中一个list，另一个list不改变
改变list内的一个对象，另一个也改变
List中ArrayList的本质还是数组，本质上区别在于是同一个数组，还是不同的数组。对于其中的对象存储的都是实例的地址，改变影响在所难免。
深复制
实体类
实现Cloneable 接口，重写clone方法注意：虽然Object中就有clone方法，但想要实现clone方法的实体类必须实现Cloneable 接口，否则实体类在调用clone方法时，会抛出异常
package com.ahut.entity;
import java.io.Serializable;
import java.util.Date;
/**
*
* @ClassName: Demo
* @Description:
* @author cheng
* @date 2017年11月21日 下午8:32:59
*/
public class Demo implements Serializable,Cloneable {
/**
* 序列化
*/
private static final long serialVersionUID = 4122974131420281791L;
private String id;
private String userName;
private int age;
private Date birthDay;
public Demo() {
super();
// TODO Auto-generated constructor stub
}
@Override
public String toString() {
return "Demo [birthDay=" + birthDay + ", userName=" + userName + ", age=" + age + ", id=" + id + "]";
}
/**
* 重写clone方法
*/
@Override
public Demo clone() throws CloneNotSupportedException {
return (Demo)super.clone();
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Date getBirthDay() {
return birthDay;
}
public void setBirthDay(Date birthDay) {
this.birthDay = birthDay;
}
}集合测试
/**
*
* @throws CloneNotSupportedException
* @Title: testCollection
* @Description:
*/
@Test
public void testCollection() throws CloneNotSupportedException{
Demo demo1 = new Demo();
demo1.setId("1234");
demo1.setUserName("demo1");
demo1.setAge(20);
demo1.setBirthDay(new Date());
Demo demo2 = new Demo();
demo2.setId("5678");
demo2.setUserName("demo2");
demo2.setAge(40);
demo2.setBirthDay(new Date());
List<Demo> demoList1 = new ArrayList<>();
demoList1.add(demo1);
demoList1.add(demo2);
// 集合深复制
List<Demo> demoList2 = new ArrayList<>();
for(Demo demo : demoList1){
demoList2.add(demo.clone());
}
System.out.println("demoList1====================================");
for(Demo demo : demoList1){
System.out.println(demo);
}
System.out.println("demoList2====================================");
for(Demo demo : demoList2){
System.out.println(demo);
}
Demo demo3 = demoList2.get(0);
demo3.setAge(9999);
System.out.println("demoList1====================================");
for(Demo demo : demoList1){
System.out.println(demo);
}
System.out.println("demoList2====================================");
for(Demo demo : demoList2){
System.out.println(demo);
}
demoList2.remove(0);
System.out.println("demoList1====================================");
for(Demo demo : demoList1){
System.out.println(demo);
}
System.out.println("demoList2====================================");
for(Demo demo : demoList2){
System.out.println(demo);
}
Demo demo4 = demoList2.get(0);
demo4.setAge(6666);
System.out.println("demoList1====================================");
for(Demo demo : demoList1){
System.out.println(demo);
}
System.out.println("demoList2====================================");
for(Demo demo : demoList2){
System.out.println(demo);
}
}结果
list1和list2操作互不干扰demoList1==================================== Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo1, age=20, id=1234] Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo2, age=40, id=5678] demoList2==================================== Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo1, age=20, id=1234] Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo2, age=40, id=5678] demoList1==================================== Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo1, age=20, id=1234] Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo2, age=40, id=5678] demoList2==================================== Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo1, age=9999, id=1234] Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo2, age=40, id=5678] demoList1==================================== Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo1, age=20, id=1234] Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo2, age=40, id=5678] demoList2==================================== Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo2, age=40, id=5678] demoList1==================================== Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo1, age=20, id=1234] Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo2, age=40, id=5678] demoList2==================================== Demo [birthDay=Tue Jan 09 21:00:03 CST 2018, userName=demo2, age=6666, id=5678]
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