clone中的浅复制和深复制
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clone：用于两个对象有相同的内容时，进行复制操作。
提示：Java中要想自定义类的对象可以被复制，自定义类就必须实现Cloneable中的clone()方法。
浅复制：另一个对象用clone()方法对已经存在的对象进行复制的时候，会改变被复制对象里面所有的内容，换句话说，浅复制就是对对象的复制出现了一些问题。
深复制：另一个对象对已有的对象进行相同的内容复制的时候，不会改变原对象的内容
什么情况下会出现浅复制呢？用下面的例子进行说明：
学生类：
public class Student implements Cloneable {
private String name;
private int age;
private Professor professor;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Professor getProfessor() {
return professor;
}
public void setProfessor(Professor professor) {
this.professor = professor;
}
@Override
public String toString() {
return "Student [name=" + name + ", age=" + age + ", professor="
+ professor + "]";
}
public Object clone() throws CloneNotSupportedException{
return super.clone();
}
}
教授类：
public class Professor {
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Professor [name=" + name + ", age=" + age + "]";
}
}
案例一：
public class ShadowCopy {
public static void main(String[] args) {
Professor p1 = new Professor();
p1.setName("Professor Zhang");
p1.setAge(30);
Student s1 = new Student();
s1.setName("xiao ming");
s1.setAge(18);
s1.setProfessor(p1);
System.out.println(s1);
try {
Student s2 = (Student) s1.clone();
Professor p2 = s2.getProfessor();
p2.setName("Professor Li");
p2.setAge(45);
s2.setProfessor(p2);
System.out.println("复制后的：s1 = " + s1);
System.out.println("复制后的：s2 = " + s2);
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
}
}
运行结果1：
1 Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]] 2 复制后的：s1 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Li, age=45]] 3 复制后的：s2 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Li, age=45]]
s1的导师为30岁的Professor Zhang，恰巧s2与s1同名同岁，但是s2的导师为45岁的Professor Li，于是我们直接复制s1给s2，再修改下s2的导师的信息。可是，问题出现了，当我们修改了s2的导师后，s2的信息是正确的，但是s1的导师信息也跟着修改了。
案例二：
public class ShadowCopy {
public static void main(String[] args) {
Professor p1 = new Professor();
p1.setName("Professor Zhang");
p1.setAge(30);
Student s1 = new Student();
s1.setName("xiao ming");
s1.setAge(18);
s1.setProfessor(p1);
System.out.println(s1);
try {
Student s2 = (Student) s1.clone();
s2.setName("xiao hong");
s2.setAge(17);
Professor p2 = s2.getProfessor();
p2.setName("Professor Li");
p2.setAge(45);
s2.setProfessor(p2);
System.out.println("复制后的：s1 = " + s1);
System.out.println("复制后的：s2 = " + s2);
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
}
}
运行结果二：
1 Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]] 2 复制后的：s1 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Li, age=45]] 3 复制后的：s2 = Student [name=xiao hong, age=17, professor=Professor [name=Professor Li, age=45]]
这次，我们在clone后，又修改了s2的name和age，从结果可以看出，s1的name和age并没有因为s2的修改而改变。
以上出现的两种情况，就是我们所说的浅复制，但我们实际上不希望出现这两种问题，如何解决呢？那我们必须就要进行深复制。接下来就是我要说的深复制
public class Professor implements Cloneable {
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Professor [name=" + name + ", age=" + age + "]";
}
public Object clone() throws CloneNotSupportedException{
return super.clone();
}
}
public class Student implements Cloneable {
private String name;
private int age;
private Professor professor;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Professor getProfessor() {
return professor;
}
public void setProfessor(Professor professor) {
this.professor = professor;
}
@Override
public String toString() {
return "Student [name=" + name + ", age=" + age + ", professor="
+ professor + "]";
}
public Object clone() throws CloneNotSupportedException{
Student newStudent = (Student) super.clone();
newStudent.professor = (Professor) professor.clone();
return newStudent;
}
}
再次运行案例一：
1.Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]] 2.复制后的：s1 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]] 3.复制后的：s2 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Li, age=45]]
再次运行案例二：
1 Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]] 2 复制后的：s1 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]] 3 复制后的：s2 = Student [name=xiao hong, age=17, professor=Professor [name=Professor Li, age=45]]
以上就是我们所说的深复制。好好去领悟哦！
参考博客：https://www.cnblogs.com/acode/p/6306887.html
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