Java的淺拷貝和深拷貝(1)

 Java的拷貝分爲深拷貝和淺拷貝

 

淺拷貝：把一個對象中所有的非static成員變量(包括對其它對象的引用，java中的引用相當於C/C++中的指針變量)都拷貝一遍，而不拷貝引用所指向的對象

深拷貝：把一個對象中所有的非static成員變量(包括對其它對象的引用)都拷貝一遍，引用所指向的對象也拷貝一份

 

這篇文章先講述淺拷貝，深拷貝下篇文章講述

 

一個類的對象如果想要具有拷貝的功能，比如符號如下條件：

   1.必須實現Cloneable接口(這個接口中沒有定義方法，叫做標記接口)

   2.重寫Object類的clone()方法，該方法實現的是淺拷貝

   3.在該類的clone()方法中的第一句，比如調用super.clone()來調用Object的clone()方法來實現拷貝

 

以下是一個淺拷貝的例子：

 

 

package com.test; public class CloneTest { public static void main(String[] args) { Student s1 = new Student(); s1.setAge(20); s1.setName("wudi"); School school = new School(); school.setName("Peiyang University"); school.setBornYear(1895); s1.setSchool(school); System.out .println("s1:" + s1.getName() + " " + s1.getAge() + " " + s1.getSchool().getName() + " " + s1.getSchool().getBornYear()); try { //拷貝一個學生 Student s2 = (Student)s1.clone(); s2.setAge(21); s2.setName("WUDI"); System.out .println("s2:" + s2.getName() + " " + s2.getAge() + " " + s2.getSchool().getName() + " " + s2.getSchool().getBornYear()); System.out.println("after s2 changing some property:"); //通過學生s2改變了他所在學校的名稱和成立時間 s2.getSchool().setName("Tianjin University"); s2.getSchool().setBornYear(1951); System.out .println("s1:" + s1.getName() + " " + s1.getAge() + " " + s1.getSchool().getName() + " " + s1.getSchool().getBornYear()); System.out .println("s2:" + s2.getName() + " " + s2.getAge() + " " + s2.getSchool().getName() + " " + s2.getSchool().getBornYear()); } catch (CloneNotSupportedException e) { e.printStackTrace(); } } } class School { private String name; private int bornYear; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getBornYear() { return bornYear; } public void setBornYear(int bornYear) { this.bornYear = bornYear; } } class Student implements Cloneable { private int age; private String name; private School school; public School getSchool() { return school; } public void setSchool(School school) { this.school = school; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override protected Object clone() throws CloneNotSupportedException { return super.clone(); } } 

 

 

從運行結果可以看出，通過學生s2將其引用school所指向的對象的name和bornYear屬性改變，相應的s1的也被改變，這說明學生s1和學生s2裏面的school引用指向的始終是同一個School對象。這就是淺拷貝的含義。