clone中的淺複製和深複製

clone：用於兩個對象有相同的內容時，進行復制操做。

提示：Java中要想自定義類的對象能夠被複制，自定義類就必須實現Cloneable中的clone()方法。

淺複製：另外一個對象用clone()方法對已經存在的對象進行復制的時候，會改變被複制對象裏面全部的內容，換句話說，淺複製就是對對象的複製出現了一些問題。

深複製：另外一個對象對已有的對象進行相同的內容複製的時候，不會改變原對象的內容

什麼狀況下會出現淺複製呢？用下面的例子進行說明：

學生類：

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();
    }

}

　　教授類：

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("複製後的：s1 = " + s1);
            System.out.println("複製後的：s2 = " + s2);
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }

    }

}

　　運行結果1：

1 Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]]
2 複製後的：s1 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Li, age=45]]
3 複製後的：s2 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Li, age=45]]

　　s1的導師爲30歲的Professor Zhang，恰巧s2與s1同名同歲，可是s2的導師爲45歲的Professor Li，因而咱們直接複製s1給s2，再修改下s2的導師的信息。但是，問題出現了，當咱們修改了s2的導師後，s2的信息是正確的，可是s1的導師信息也跟着修改了。

 

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("複製後的：s1 = " + s1);
            System.out.println("複製後的：s2 = " + s2);
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }

    }

}

　　運行結果二：

1 Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]]
2 複製後的：s1 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Li, age=45]]
3 複製後的：s2 = Student [name=xiao hong, age=17, professor=Professor [name=Professor Li, age=45]]

　　此次，咱們在clone後，又修改了s2的name和age，從結果能夠看出，s1的name和age並無由於s2的修改而改變。

　　以上出現的兩種狀況，就是咱們所說的淺複製，但咱們實際上不但願出現這兩種問題，如何解決呢？那咱們必須就要進行深複製。接下來就是我要說的深複製

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;
    }

}

　　再次運行案例一：

1.Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]]
2.複製後的：s1 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]]
3.複製後的：s2 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Li, age=45]]

　　

　　再次運行案例二：

1 Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]]
2 複製後的：s1 = Student [name=xiao ming, age=18, professor=Professor [name=Professor Zhang, age=30]]
3 複製後的：s2 = Student [name=xiao hong, age=17, professor=Professor [name=Professor Li, age=45]]

　　以上就是咱們所說的深複製。好好去領悟哦！

　　參考博客：https://www.cnblogs.com/acode/p/6306887.html