多态

/**
 * 父类
 */
class BaseClass {
    
    void printBase() {
        System.out.println("i am a base method");
    }

    void printStr() {
        System.out.println("i am a method in BaseClass!");
    }
}

/**
 * 子类
 */
class SubClass extends BaseClass {

    @Override
    void printStr() {
        System.out.println("i am a method in SubClass!");
    }

    void printSub() {
        System.out.println("i am a sub method");
    }
}

/**
 * 多态的代码理解
 */
public class Polymorphism {
    public static void main(String[] args) {

        // 父类自身调用自身的类方法
        BaseClass bs = new BaseClass();
        bs.printBase();                 // i am a base method
        bs.printStr();                  // i am a method in BaseClass!

        // 子类自身调用自身的类方法
        SubClass sc = new SubClass();
        sc.printStr();                  // i am a method in SubClass!
        sc.printSub();                  // i am a sub method
        sc.printBase();                 // i am a base method

        // 多态
        BaseClass polymorphism = new SubClass();
        // 父类对象调用子类方法
        polymorphism.printStr();        // i am a method in SubClass!
        // 父类对象调用自身方法
        polymorphism.printBase();       // i am a base method
    }
}

组合

class HumanClass {

    void breath() {
        System.out.println("breath ~");
    }

    void sleep() {
        System.out.println("sleep ~");
    }

    void eat() {
        System.out.println("eat ~");
    }
}

class StuClass {

    private HumanClass human;

    StuClass(HumanClass human) {
        this.human = human;
    }

    void breath() {
        human.breath();
    }

    void study() {
        System.out.println("study ~");
    }
}

class WorkerClass {

    private HumanClass human;

    WorkerClass(HumanClass human) {
        this.human = human;
    }

    void eat() {
        human.eat();
    }

    void work() {
        System.out.println("work ~");
    }
}

public class Combination {
    public static void main(String[] args) {

        HumanClass jack = new HumanClass();
        jack.eat();
        jack.breath();
        jack.sleep();

        StuClass jess = new StuClass(jack);
        jess.breath();
        jess.study();

        WorkerClass li = new WorkerClass(jack);
        li.eat();
        li.work();
    }
}

继承

/**
 * 父类
 */
class HumanClass {

    void breath() {
        System.out.println("breath ~");
    }

    void sleep() {
        System.out.println("sleep ~");
    }

    void eat() {
        System.out.println("eat ~");
    }
}

/**
 * 子类
 */
class StuClass extends HumanClass {

    void study() {
        System.out.println("study ~");
    }
}

class WorkerClass extends HumanClass{

    void work() {

        System.out.println("work ~");
    }
}

public class Inherit {
    public static void main(String[] args) {
        HumanClass jack = new HumanClass();
        jack.breath();
        jack.eat();
        jack.sleep();

        StuClass jess = new StuClass();
        jess.study();
        jess.breath();
        jess.eat();
        jess.sleep();

        WorkerClass li = new WorkerClass();
        li.work();
        li.breath();
        li.eat();
        li.sleep();
    }
}