clone java 安全 java clone原理

解析java中的clone方法

1 是什么

clone方法是Object类中的一个被protected和native修饰的方法,被native就代表它的实现源码是用c++实现的,只不过是我们无法去修改它的代码罢了。

2 作用

为子类提供可以重写的clone()方法,目的是实现对象的浅克隆和深克隆

3 如何用

3.1 前提

3.1.1 克隆的原理

在堆内存中新开辟一段空间,然后把被克隆对象的属性和方法赋值一份到新开辟的空间里面(副本)。

3.2 浅克隆

3.2.1 原理

对于基本数据类型而言,是复制其的副本到新开辟的空间里面

对于引用数据类型而言,只是复制了引用的地址,并没有开辟新的空间,新的空间里面的引用和被克隆的里面的引用都指向于同一个空间

3.2.2 浅克隆的实现步骤

a 实现cloneable接口,这个是判断能否克隆的条件

b 重写Clone方法,建议采用如下所示的写法

public 被克隆对象的类型 clone(){
    //不要上抛异常,在方法体里面处理异常以及进行向下转型
   被克隆对象的类型 对象名=null;
   try {
       对象名=(被克隆对象的类型)super.clone();
  } catch (CloneNotSupportedException e) {
            e.printStackTrace();
  }
   return 对象名;
}

3.2.3 示例代码

Hero

package Work;
//英雄类,因为需要用克隆,需要实现Cloneable接口
public class Hero implements Cloneable {
    private String name;
    //名字
    private int attack;
    //攻击力
    private int defence;
    //防御力
    private Weapon weapon;
    //武器

    public Hero() {
    }

    public Hero(String name, int attack, int defence, Weapon weapon) {
        this.name = name;
        this.attack = attack;
        this.defence = defence;
        this.weapon = weapon;
    }

    public String getName() {
        return name;
    }

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

    public int getAttack() {
        return attack;
    }

    public void setAttack(int attack) {
        this.attack = attack;
    }

    public int getDefence() {
        return defence;
    }

    public void setDefence(int defence) {
        this.defence = defence;
    }

    public Weapon getWeapon() {
        return weapon;
    }

    public void setWeapon(Weapon weapon) {
        this.weapon = weapon;
    }

    @Override
    public String toString() {
        return "Hero{" +
                "name='" + name + '\'' +
                ", attack=" + attack +
                ", defence=" + defence +
                ", weapon=" + weapon +
                '}';
    }

    @Override
    public  Hero clone(){
        Hero hero=null;
        try {
            hero=(Hero)super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return hero;
    }
}

Weapon

package Work;

public class Weapon implements Cloneable{
    private String name;
    //名字
    private int bonusAttack;
    //攻击力加成
    private int durable;
    //耐久值

    public Weapon() {
    }

    public Weapon(String name, int bonusAttack, int durable) {
        this.name = name;
        this.bonusAttack = bonusAttack;
        this.durable = durable;
    }

    public String getName() {
        return name;
    }

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

    public int getBonusAttack() {
        return bonusAttack;
    }

    public void setBonusAttack(int bonusAttack) {
        this.bonusAttack = bonusAttack;
    }

    public int getDurable() {
        return durable;
    }

    public void setDurable(int durable) {
        this.durable = durable;
    }

    @Override
    public String toString() {
        return "Weapon{" +
                "name='" + name + '\'' +
                ", bonusAttack=" + bonusAttack +
                ", durable=" + durable +
                '}';
    }

    @Override
    public Weapon clone() {
        Weapon weapon=null;
        try {
            weapon=(Weapon)super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return weapon;
    }
}

TestHero

package Work;
public class TestHero {
    public static void main(String[] args) {
        Hero hero=new Hero("亚瑟",200,100,new Weapon("屠龙",100,1000));
        Hero copyHero=hero.clone();
        copyHero.getWeapon().setDurable(467);
        copyHero.setName("阿古多");
        System.out.println(hero);
        System.out.println(copyHero);
    }
}

3.2.4 示例代码的内存原理图

a 克隆后

b 更改String属性和引用数据类型属性后

3.2.5 示例代码运行截图

3.3 深克隆

3.3.1 原理

对于基本数据类型而言,是复制其的副本到新开辟的空间里面

对于引用数据类型而言,并不是复制了引用的地址,而是开辟了一个新的引用对象的空间,并把引用地址里面的属性和方法拷贝一份到新的引用对象的空间中,此时克隆对象里面的引用就指向于这个新的空间

3.3.2 示例代码

Hero类

package Work;
//英雄类,因为需要用克隆,需要实现Cloneable接口
public class Hero implements Cloneable {
    private String name;
    //名字
    private int attack;
    //攻击力
    private int defence;
    //防御力
    private Weapon weapon;
    //武器

    public Hero() {
    }

    public Hero(String name, int attack, int defence, Weapon weapon) {
        this.name = name;
        this.attack = attack;
        this.defence = defence;
        this.weapon = weapon;
    }

    public String getName() {
        return name;
    }

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

    public int getAttack() {
        return attack;
    }

    public void setAttack(int attack) {
        this.attack = attack;
    }

    public int getDefence() {
        return defence;
    }

    public void setDefence(int defence) {
        this.defence = defence;
    }

    public Weapon getWeapon() {
        return weapon;
    }

    public void setWeapon(Weapon weapon) {
        this.weapon = weapon;
    }

    @Override
    public String toString() {
        return "Hero{" +
                "name='" + name + '\'' +
                ", attack=" + attack +
                ", defence=" + defence +
                ", weapon=" + weapon +
                '}';
    }

    @Override
    public  Hero clone(){
        Hero hero=null;
        try {
            hero=(Hero)super.clone();
            //给weapon属性也给克隆一下
            setWeapon(getWeapon().clone());
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return hero;
    }
}

Weapon类

package Work;

public class Weapon implements Cloneable{
    private String name;
    //名字
    private int bonusAttack;
    //攻击力加成
    private int durable;
    //耐久值

    public Weapon() {
    }

    public Weapon(String name, int bonusAttack, int durable) {
        this.name = name;
        this.bonusAttack = bonusAttack;
        this.durable = durable;
    }

    public String getName() {
        return name;
    }

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

    public int getBonusAttack() {
        return bonusAttack;
    }

    public void setBonusAttack(int bonusAttack) {
        this.bonusAttack = bonusAttack;
    }

    public int getDurable() {
        return durable;
    }

    public void setDurable(int durable) {
        this.durable = durable;
    }

    @Override
    public String toString() {
        return "Weapon{" +
                "name='" + name + '\'' +
                ", bonusAttack=" + bonusAttack +
                ", durable=" + durable +
                '}';
    }

    @Override
    public Weapon clone() {
        Weapon weapon=null;
        try {
            weapon=(Weapon)super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return weapon;
    }
}

TestHero类

package Work;
public class TestHero {
    public static void main(String[] args) {
        Hero hero=new Hero("亚瑟",200,100,new Weapon("屠龙",100,1000));
        Hero copyHero=hero.clone();
        copyHero.getWeapon().setDurable(467);
        copyHero.setAttack(500);
        copyHero.setName("阿古多");
        System.out.println(hero);
        System.out.println(copyHero);
    }
}

3.3.3 示例代码的内存原理图

a 克隆后

b 修改克隆对象的属性和方法

3.3.4 示例代码运行截图