java深拷贝和浅拷贝

一：
java中要想使对象具有拷贝的功能，必须实现Cloneable接口（Cloneable接口是一个标识接口，标识这个类可以被clone），并且在类中自定义clone调用Object类提供的继承权限clone方法。

public interface Cloneable {
}

只有子类实现了Cloneable接口后才可以使用Object类提供的clone方法。

protected native Object clone() throws CloneNotSupportedException;

二：
浅拷贝：对象值拷贝。
对于浅拷贝而言，拷贝出来的对象依然保留原对象的所有引用。（牵一发而动全身）。
只要任意一个拷贝对象（或原对象）中的引用发生改变，所有对象都会受到影响。

代码范例：

class Teacher {
    private String name;
    private String skill;

    public Teacher(String name, String skill) {
        this.name = name;
        this.skill = skill;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSkill() {
        return skill;
    }

    public void setSkill(String skill) {
        this.skill = skill;
    }

    @Override
    public String toString() {
        return "Teacher{" +
                "name='" + name + '\'' +
                ", skill='" + skill + '\'' +
                '}';
    }
}

class Student implements Cloneable {
    private String name;
    private int age;
    private Teacher teacher;

    public Student(String name, int age, Teacher teacher) {
        this.name = name;
        this.age = age;
        this.teacher = teacher;
    }

    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 Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", teacher=" + teacher +
                '}';
    }

    @Override
    protected Student clone() throws CloneNotSupportedException {
        Student student = null;
        student = (Student) super.clone();
        return student;
    }
}

public class TestClone {
    public static void main(String[] args) {
        Teacher teacher = new Teacher("Peter", "basketball");
        Student student = new Student("Alice", 18, teacher);
        System.out.println(teacher);
        System.out.println(student);
        try {
            Student cloneStudent = student.clone();
            System.out.println(cloneStudent);
            System.out.println(cloneStudent.getAge());
            System.out.println(cloneStudent.getName());
            System.out.println(cloneStudent.getTeacher());
            System.out.println(teacher == cloneStudent.getTeacher());//true
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
    }
}

运行结果：

Teacher{name='Peter', skill='basketball'}
Student{name='Alice', age=18, teacher=Teacher{name='Peter', skill='basketball'}}
Student{name='Alice', age=18, teacher=Teacher{name='Peter', skill='basketball'}}
18
Alice
Teacher{name='Peter', skill='basketball'}
true

Process finished with exit code 0

可以看出：浅拷贝出来的对象中仍然保留着原来对象中其他类的引用，即对象包含的其他对象并未产生新的对象。

深拷贝：拷贝出来的对象产生了所有引用的新的对象。

实现深拷贝的的两种方式：
1…包含的其他类继续实现Cloneable接口，并且调用clone方法(递归实现Clone)。
2.序列化。
使用序列化进行深拷贝时，无须再实现Cloneable接口，只需要实现Serializable即可。
代码范例：

class Teacher implements Serializable{
    private String name;
    private String skill;

    public Teacher(String name, String skill) {
        this.name = name;
        this.skill = skill;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSkill() {
        return skill;
    }

    public void setSkill(String skill) {
        this.skill = skill;
    }

    @Override
    public String toString() {
        return "Teacher{" +
                "name='" + name + '\'' +
                ", skill='" + skill + '\'' +
                '}';
    }


}
class Student implements Serializable{
    private String name;
    private int age;
    private Teacher teacher;

    public Student(String name, int age, Teacher teacher) {
        this.name = name;
        this.age = age;
        this.teacher = teacher;
    }

    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 Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", teacher=" + teacher +
                '}';
    }

    public Student cloneObject() throws IOException, ClassNotFoundException {
        //使用内存流进行序列化操作
        ByteOutputStream bos = new ByteOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(this);
        ByteArrayInputStream bis = new ByteArrayInputStream(bos.getBytes());
        ObjectInputStream ois = new ObjectInputStream(bis);
        return (Student) ois.readObject();
    }
}

public class TextDeepClone {
    public static void main(String[] args) {
        Teacher teacher = new Teacher("Peter","basketball");
        Student student = new Student("Alice",18,teacher);
        try {
            Student cloneStudent = student.cloneObject();
            System.out.println(student);//Alice,18,Peter,"basketball"
            System.out.println(cloneStudent);//Alice,18,Peter,"basketball"
            System.out.println(cloneStudent.getName());
            System.out.println(cloneStudent.getAge());
            System.out.println(cloneStudent.getTeacher().getName());
            System.out.println(cloneStudent.getTeacher().getSkill());
            System.out.println(student == cloneStudent);//false

        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

运行结果：

Student{name='Alice', age=18, teacher=Teacher{name='Peter', skill='basketball'}}
Student{name='Alice', age=18, teacher=Teacher{name='Peter', skill='basketball'}}
Alice
18
Peter
basketball
false

Process finished with exit code 0

特点：修改任意一个对象，不会对其他对象产生影响。

            cloneStudent.setAge(20);
            System.out.println(student);
            System.out.println(cloneStudent);

结果：

Student{name='Alice', age=18, teacher=Teacher{name='Peter', skill='basketball'}}
Student{name='Alice', age=20, teacher=Teacher{name='Peter', skill='basketball'}}