Java中浅拷贝和深拷贝

引入

浅拷贝

浅拷贝仅仅复制所考虑的对象，而不复制它所引用的对象。

实现Cloneable重写clone

注：此方法默认是浅克隆

定义两个类Teacher和Student

Teacher类：

class Teacher implements Cloneable {
    String name;

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

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

Student类：

class Student implements Cloneable {
    String name;
    Integer id;
    Teacher teacher;

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

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

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

测试：

public class CopyTest {
        public static void main(String[] args) throws Exception {
            Teacher teacher = new Teacher("李四老师");
            Student student = new Student("张三", 12, teacher);
            Student cloneStudent = (Student) student.clone();
            System.out.println(student);
            System.out.println(cloneStudent);
            teacher.name = "王五老师";
            System.out.println("=========修改老师信息后=========");
            System.out.println(student);
            System.out.println(cloneStudent);
        }
    }
}

输出结果：

Student{name='张三', id=12, teacher=Teacher{name='李四老师'}}
Student{name='张三', id=12, teacher=Teacher{name='李四老师'}}
=========修改老师信息后=========
Student{name='张三', id=12, teacher=Teacher{name='王五老师'}}
Student{name='张三', id=12, teacher=Teacher{name='王五老师'}}

图解：

分析：

两个student和cloneStudent指向不同的对象，但是两个引用student和copyStudent中的teacher引用指向的是同一个对象，所以说是浅拷贝。

深拷贝

深拷贝是把要复制的对象所引用的对象都复制一遍。

Teacher类：

class Teacher implements Cloneable {
    String name;

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

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

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

Student类：

class Student implements Cloneable {
    String name;
    Integer id;
    Teacher teacher;

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

    @Override
    protected Object clone() throws CloneNotSupportedException {
        // 浅复制时
        // return super.clone();

        //深复制时
        Student student = (Student) super.clone();
        student.teacher = (Teacher) student.teacher.clone();
        return student;
    }

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

测试代码：

Teacher teacher1 = new Teacher("李四老师");
Student student = new Student("张三", 12, teacher1);
Student cloneStudent = (Student) student.clone();
System.out.println(student);
System.out.println(cloneStudent);

teacher.name = "王五老师";
System.out.println("=========修改老师信息后=========");
System.out.println(student);
System.out.println(cloneStudent);

结果：

Student{name='张三', id=12, teacher=Teacher{name='李四老师'}}
Student{name='张三', id=12, teacher=Teacher{name='李四老师'}}
=========修改老师信息后=========
Student{name='张三', id=12, teacher=Teacher{name='王五老师'}}
Student{name='张三', id=12, teacher=Teacher{name='李四老师'}}

结果分析：

两个引用student和copyStudent 指向不同的对象，这两个对象中的成员变量teacher是指向的两个对象，对teacher1修改只能影响到student对象，所以说是深拷贝。

图解（teacher姓名更改前）

图解（teacher姓名更改后）