先看一个简单案例
public class Test {public static void main(String args[]) {Student stu1 = new Student();stu1.number = 1;Student stu2 = stu1;//stu1和stu2指向堆内存中同一个对象System.out.println("学生1：" + stu1.number + " 学生2：" + stu2.number);stu2.number = 2;System.out.println("学生1：" + stu1.number + " 学生2：" + stu2.number);System.out.println(stu1 == stu2);}}class Student {public int number;}
如上这种形式，仅仅将一个对象的引用赋给另一个引用，并没有复制出另一个对象，这两个引用指向的是内存中的同一个对象所以，这根本不叫对象的复制
对象的复制(浅复制)
public class Test {public static void main(String args[]) {Student stu1 = new Student();stu1.number = 1;Student stu2 = (Student) stu1.clone();System.out.println("学生1：" + stu1.number + " 学生2：" + stu2.number);stu2.number = 2;System.out.println("学生1：" + stu1.number + " 学生2：" + stu2.number);System.out.println(stu1 == stu2);}}class Student implements Cloneable {public int number;@Overridepublic Object clone() {Student stu = null;try {stu = (Student) super.clone();} catch (CloneNotSupportedException e) {e.printStackTrace();}return stu;}}
Object有个protected的clone方法，该方法的签名是：protected native Object clone() throws CloneNotSupportedException;要想对一个对象进行复制，就需要覆盖clone方法，一般步骤是（浅复制）：
- 1、被复制的类需要实现Clonenable接口，不实现的话在调用clone方法会抛出CloneNotSupportedException异常，该接口为标记接口(不含任何方法)
- 2、覆盖clone()方法，访问修饰符设为public。方法中调用super.clone()方法得到需要的复制对象（native为本地方法)
浅复制可能出现的问题
public class Test {public static void main(String args[]) {Student stu1 = new Student();stu1.number = 1;stu1.address = new Address("广州");stu1.courseList.add("语文");//复制stu1Student stu2 = (Student) stu1.clone();System.out.println("学生1：" + stu1.number + " " + stu1.address + " " + stu1.courseList);System.out.println("学生2：" + stu2.number + " " + stu2.address + " " + stu2.courseList);//更改stu2stu2.number = 2;stu2.address = new Address("深圳");stu2.courseList.add("数学");System.out.println("学生1：" + stu1.number + " " + stu1.address + " " + stu1.courseList);System.out.println("学生2：" + stu2.number + " " + stu2.address + " " + stu2.courseList);}}class Student implements Cloneable {public int number;public ArrayList<String> courseList = new ArrayList<String>();public Address address;@Overridepublic Object clone() {Student stu = null;try {stu = (Student) super.clone();} catch (CloneNotSupportedException e) {e.printStackTrace();}return stu;}}class Address {public String add;public Address(String add) {this.add = add;}}
更改stu2的address和courseList后，是不是发现，stu1的相应值也变了？这是为什么呢？这是因为Java做了一个偷懒的拷贝动作，Object类提供的方法clone只是拷贝本对象，其对象内部的数组、引用对象等都不拷贝，还是指向原生对象的内部元素的地址，这种拷贝就叫做浅拷贝。确实是非常浅，两个对象共享了一个私有变量，你改我改大家都能改，是一个种非常不安全的方式，在实际项目中使用还是比较少的。注意：八大基本类型和String(虽然String 是引用类型，但Java其实是希望你把它也"认为"是基本类型，String 是没有 clone 方法的)等都会被拷贝的。
深复制
public class Test {public static void main(String args[]) {Student stu1 = new Student();stu1.number = 1;stu1.address = new Address("广州");stu1.courseList.add("语文");//复制stu1Student stu2 = (Student) stu1.clone();System.out.println("学生1：" + stu1.number + " " + stu1.address + " " + stu1.courseList);System.out.println("学生2：" + stu2.number + " " + stu2.address + " " + stu2.courseList);//更改stu2stu2.number = 2;stu2.address = new Address("深圳");stu2.courseList.add("数学");System.out.println("学生1：" + stu1.number + " " + stu1.address + " " + stu1.courseList);System.out.println("学生2：" + stu2.number + " " + stu2.address + " " + stu2.courseList);}}class Student implements Cloneable {public int number;public ArrayList<String> courseList = new ArrayList<String>();public Address address;@SuppressWarnings("unchecked")@Overridepublic Object clone() {Student stu = null;try {stu = (Student) super.clone();//浅复制stu.address = (Address) address.clone(); //深度复制stu.courseList = (ArrayList<String>) courseList.clone();//深度复制} catch (CloneNotSupportedException e) {e.printStackTrace();}return stu;}}class Address implements Cloneable {//为了达到真正的复制对象，而不是纯粹引用复制。我们需要将Address类可复制化public String add;public Address(String add) {this.add = add;}@Overridepublic Object clone() {Address addr = null;try {addr = (Address) super.clone();} catch (CloneNotSupportedException e) {e.printStackTrace();}return addr;}}