Feeder feeder=new Feeder();Animal animal=new Dog();Food food=new Bon();feeder.feed(animal,food);//给狗喂肉狗骨头anmal=new Cat();foof=new Fish();feeder.feed(animal,food);给猫喂鱼

class Base{String var="BaseVar";           //实例变量static String staticvar="StaticBaseVar"  //静态变量void metod()           //实例方法system.out.Println("Base method");}static void staticMethod()  //静态方法{syso.out.printIn("Static Base method");}}public class Sub extends Base{String var="Subvar";  static String staticVar="staticSubvar";void method()  //覆盖父类的method()方法{Sysotem.out.printIn("Static sub method");}static void staticMethod()  //隐藏父类的staticMethod()方法{system.out.printin("static sub method");}String subVar="Var only belonging to  sub";void subMethod(){System.out.pritn("Method only belonging to sub");}public static void main(String args[]){Base who=new Sub();                  //who被声明为Base类型，引用SubSystem.out.printin("who.var"+who.var);  //打印Base类的var变量System.out.printIn("who.staticVar"+wh.saticVar); //打印Base类staticVar变量who.metod();             //打印Sub实例的method()方法who.staticMethod();        //打印Base类的staticMethod();}}