结果：（我怎么理解的是注释的结果啊）
Frog swim
Frog speak
Frog eat
Frog grow
Frog eat            //Amphibian eat
Amphibian grow
Frog eat           // Amphibian eat



import static org.greggordon.tools.Print.*;

class Amphibian {
    protected void swim() {
        println("Amphibian swim");
    }
    protected void speak() {
        println("Amphibian speak");
    }
    void eat() {
        println("Amphibian eat");
    }
    static void grow(Amphibian a) {
        println("Amphibian grow");
        a.eat();
    }
}

public class Frog17 extends Amphibian {
    @Override protected void swim() {
        println("Frog swim");
    }
    @Override protected void speak() {
        println("Frog speak");
    }
    @Override void eat() {
        println("Frog eat");
    }
    static void grow(Amphibian a) {
        println("Frog grow");
        a.eat();
    }
    public static void main(String[] args) {
        Frog17 f = new Frog17();
        // call overridden base-class methods:
        f.swim();
        f.speak();
        f.eat();
        // upcast Frog17 to Amphibian argument:
        f.grow(f);
                   //调导出类的方法，f向上转型为基类型，然后导出类中a.eat（）是不是应该调基类的eat（）啊
        // upcast Frog17 to Amphibian and call Amphibian method:
        Amphibian.grow(f);//调基类方法，参数向上转型基类型，然后a.eat()不应该是掉基类的eat么
    }
}

import static org.greggordon.tools.Print.*;

class Component1 {
    Component1() { println("Component1()"); }
}

class Component2 {
    Component2() { println("Component2()"); }
}

class Component3 {
    Component3() { println("Component3()"); }
}

class Root {
    Component1 c1root=new Component1() ;
    Component2 c2root;
    Component3 c3root;
    Root() { println("Root()"); }
}

class Stem extends Root {
    Component1 c1stem;
    Component2 c2stem=new Component2();
    Component3 c3stem;
    Stem() { println("Stem()"); }
    public static void main(String[] args) {
        Stem s = new Stem();
    }
}