Java基础 5.27

最新推荐文章于 2025-12-11 08:58:14 发布

原创最新推荐文章于 2025-12-11 08:58:14 发布 · 322 阅读

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多态注意事项和细节讨论

属性没有重写之说属性的值看编译类型

package com.logic.poly_.detail_;

public class PolyDetail02 {
    public static void main(String[] args) {
        Base base = new Sub();
        System.out.println(base.count);
        Sub sub = new Sub();
        System.out.println(sub.count);
    }
}

class Base {
    int count = 10;
}

class Sub extends Base {
    int count = 20;
}

instanceOf比较操作符用于判断对象的运行类型是否为XX类型或XX类型的子类型

package com.logic.poly_.detail_;

public class PolyDetail03 {
    public static void main(String[] args) {
        //编译类型是BB 运行类型是BB
        BB bb = new BB();
        System.out.println(bb instanceof BB);
        System.out.println(bb instanceof AA);
        //编译类型是AA 运行类型是BB
        AA aa = new BB();
        System.out.println(aa instanceof AA);
        System.out.println(aa instanceof  BB);

        Object obj = new Object();
        System.out.println(obj instanceof AA);
        String str = "logic";
        System.out.println(str instanceof Object);
    }
}

class AA {} //父类
class BB extends AA{} //子类

多态练习

package com.logic.poly_.detail_;

public class PolyPractice {
    public static void main(String[] args) {
        double d = 13.4;//ok
        long i = (long)d;//ok
        System.out.println(i);//13
        int in = 5;//ok
        boolean b = (boolean)in;//不对 boolean -> int
        Object obj = "hello";//ok 向上转型
        String objStr = (String) obj;//ok 向下转型
        System.out.println(objStr);//hello
        
        Object objPri = new Integer(5);//ok 向上转型
        String str = (String) objPri;//不对 ClassCastException
        //指向Integer的父类引用 转成String
        Integer str1 = (Integer) objPri;//ok 向下转型
    }
}

package com.logic.poly_.detail_;

public class PolyPractice02 {
    public static void main(String[] args) {
        B b = new B();
        System.out.println(b.count);//20
        b.display();//20
        A a = b;
        System.out.println(a == b);//true
        System.out.println(a.count);//10
        a.display();//20
    }
}
class A {
    public int count = 10;

    public void display() {
        System.out.println(this.count);
    }
}
class B extends A {
    public int count = 20;

    public void display() {
        System.out.println(this.count);
    }
}