java基础——浅克隆与深克隆

摘要：为什么使用存在一个对象，已有初始值，这时候可能需要一个新的对象和相同，但是和是两个独立的对象，任意一个改动都不影响其中一个的值，但是的初始值由确定，这时候就是最有效也是最简单的方法。

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。

需要克隆的对象要继承Cloneable接口，并重写clone()方法

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

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

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 ;
    }
}

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

Teacher继承Cloneable

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