clone中的浅复制和深复制

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