Java 深复制和浅复制

信息

日期 : 2016-7-5 7:12:30

基本概念

浅复制：

被复制对象的所有变量都含有与原来的对象相同的值，而所有的对其他对象的引用仍然指向原来的对象。换言之，浅复制仅仅复制所考虑的对象，而不复制它所引用的对象。

深复制：

被复制对象的所有变量都含有与原来的对象相同的值，除去那些引用其他对象的变量。那些引用其他对象的变量将指向被复制过的新对象，而不再是原有的那些被引用的对象。换言之，深复制把要复制的对象所引用的对象都复制了一遍。

深复制（clone()）

1. 实现 Cloneable 接口，对象的引用也需要实现该方法。
2. 重载 clone() 方法。

具体代码

Teacher

public class Teacher implements Cloneable, Serializable {

    private String name;

    public String getName() {
        return name;
    }

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

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

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

Student

public class Student implements Cloneable, Serializable{

    private String name;

    private Teacher teacher;

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

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

    //深复制
    public Object deepCopy () throws IOException, ClassNotFoundException {
        ByteArrayOutputStream bo = new ByteArrayOutputStream();
        ObjectOutputStream oo = new ObjectOutputStream(bo);
        oo.writeObject(this);
        //从流里读出来
        ByteArrayInputStream bi = new ByteArrayInputStream(bo.toByteArray());
        ObjectInputStream oi = new ObjectInputStream(bi);
        return (oi.readObject());
    }

    public String getName() {
        return name;
    }

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

    public Teacher getTeacher() {
        return teacher;
    }

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

测试类

public class StudentTest {

    @Test
    public void testDeepCopy() throws CloneNotSupportedException, IOException, ClassNotFoundException {
        Teacher teacher = new Teacher("teacher");
        Student student = new Student("student", teacher);

        //进行深复制
        Student studentCopy = (Student) student.clone();
        Student studentCopy1 = (Student) student.deepCopy();
        //
        Assert.assertNotEquals(student, studentCopy);
        Assert.assertNotEquals(student.getTeacher(), studentCopy.getTeacher());
        Assert.assertNotEquals(student.getTeacher(), studentCopy1.getTeacher());

    }

}

深复制---序列化实现

在Java中有一个 Serializable 接口，实现该接口的对象都有一个序列化标志，可以直接使用java的对象写入方法，把实现序列化接口的对象写入到输出流中，然后再把输入流转换为对象，由此可以实现对象的深层复制。通过一些java关键字的控制，可以屏蔽一些不想复制的字段。

具体代码

Teacher

public class Teacher implements Cloneable, Serializable {

    private String name;

    public String getName() {
        return name;
    }

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

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

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

Student

public class Student implements Cloneable, Serializable{

    private String name;

    private Teacher teacher;

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

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

    //深复制
    public Object deepCopy () throws IOException, ClassNotFoundException {
        ByteArrayOutputStream bo = new ByteArrayOutputStream();
        ObjectOutputStream oo = new ObjectOutputStream(bo);
        oo.writeObject(this);
        //从流里读出来
        ByteArrayInputStream bi = new ByteArrayInputStream(bo.toByteArray());
        ObjectInputStream oi = new ObjectInputStream(bi);
        return (oi.readObject());
    }

    public String getName() {
        return name;
    }

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

    public Teacher getTeacher() {
        return teacher;
    }

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

测试类

public class StudentTest {

    @Test
    public void testDeepCopy() throws CloneNotSupportedException, IOException, ClassNotFoundException {
        Teacher teacher = new Teacher("teacher");
        Student student = new Student("student", teacher);

        //进行深复制
        Student studentCopy = (Student) student.clone();
        Student studentCopy1 = (Student) student.deepCopy();
        //
        Assert.assertNotEquals(student, studentCopy);
        Assert.assertNotEquals(student.getTeacher(), studentCopy.getTeacher());
        Assert.assertNotEquals(student.getTeacher(), studentCopy1.getTeacher());

    }

}