java基础浅克隆与深克隆

为什么使用 clone

存在一个对象 A，A 已有初始值，这时候可能需要一个新的对象 B 和 A 相同，但是 A 和 B 是两个独立的对象，任意一个改动都不影响其中一个的值，但是 B 的初始值由 A 确定，这时候 clone 就是最有效也是最简单的方法。

new 一个对象和 clone 一个对象的区别

• new 操作符的本意是分配内存空间，java 程序执行到 new 操作符时，首先去看 new 操作符后面的类型，知道类型才能知道需要分配多大的内存空间，分配完成，调用构造函数，填充对象，完成对象的初始化。
• clone 的第一步也是分配内存，java 程序执行到 clone 这一步时，分配的内存和调用 clone 方法的对象相同，在根据原对象完成对新对象的初始化，一个新的对象就被创建完成。

复制对象和克隆对象

需要克隆的对象要继承 Cloneable 接口，并重写 clone() 方法

复制对象

定义类：

public class People1 {
    private String name;
    private Integer age;

    public People1(String name, Integer age) {
        this.name = name;
        this.age = age;
    }
}

复制测试

public class test {public static void main(String[] args) {People1 people1 = new People1("people",18);
        People1 people11 = people1;

        System.out.println(people1);
        System.out.println(people11);
        System.out.println(people1 == people11);
    }
}

结果：

证明复制对象只是指向原来的对象，people1 和 people11 只是引用同一个对象

clone 对象

定义类：

public class People2 implements Cloneable{
    private String name;
    private Integer age;

    public People2(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {return name;}

    public Integer getAge() {return age;}
    
    public void setName(String name) {this.name = name;}

    public void setAge(Integer age) {this.age = age;}
    @Override
    protected Object clone() throws CloneNotSupportedException {return super.clone();
    }
}

测试：

public class test {public static void main(String[] args) {
        
        //clone
        People2 people2 = new People2("people",18);
        People2 people22 = null;
        try {people22 = (People2) people2.clone();} catch (CloneNotSupportedException e) {e.printStackTrace();
        }

        System.out.println(people2);
        System.out.println(people22);
        System.out.println(people2 == people22);
    }
}

结果：

可以看出 people2 和 people22 指向的对象并不是同一个的

浅克隆与深克隆

定义类：
Student 类：

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

    public Student(String name, Integer 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 Integer getAge() {return age;}

    public void setAge(Integer age) {this.age = age;}

    public Teacher getTeacher() {return teacher;}

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

    @Override
     public String toString() {return "学生：name=" + name + ", age=" + age + ", 指导" + teacher;}

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

Teacher 类

public class Teacher {
    private String name;
    private Integer age;

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

    public String getName() {return name;}

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

    public Integer getAge() {return age;}

    public void setAge(Integer age) {this.age = age;}
    @Override
    public String toString() {return "老师：name=" + name + ", age=" + age ;}
}

浅克隆

main 函数

public class test2 {public static void main(String[] args) {Teacher teacher = new Teacher("刘老师",18);
        Student student1 = new Student("小明",10,teacher);
        Student student2 = null;
        try {student2 = (Student) student1.clone();} catch (CloneNotSupportedException e) {e.printStackTrace();
        }
        Teacher t1 = student2.getTeacher();
        t1.setName("张老师");
        t1.setAge(30);
        student2.setName("小红");
        student2.setAge(9);
        student2.setTeacher(t1);
        System.out.println(student1);
        System.out.println(student2);
    }
}

结果：

修改 student2 中的 Teacher 类，student1 也跟着改变，而修改姓名和年龄并不会修改，由此得出才重新 clone 方法时不能直接 super

深克隆

1. Teacher 继承 Cloneable
2. Student 重写 clone 方法

        Student newStudent = (Student) super.clone();
        newStudent.teacher = (Teacher) teacher.clone();
        return newStudent;

运行上方测试代码，结果：

完成预想结果