教程书里说如果添加其他类直接在main函数后面添加，可是我自己试了一下不行，怎么回事？

[loveypv520]

public class Pets {


private String petsName;
public String getPetsName(){
return petsName;
}

public void setPetsName(String petsName){
this.petsName=petsName;
}
//  下面是构造方法
public Pets(){

}
public Pets(String petsName){
this.petsName=petsName;
}
public void eat(){ //声明eat变量
System.out.println(petsName+"eating foods");
}

public class Instrument{ //创建instrument类
private String instrmentName; //instrmentname 为私有
public String getInstrmentName(){
return instrmentName;

}
public void setInstrmentName(String InstrmentName){
this.instrmentName=instrmentName;
}
public Instrument(String instrmentName){
this.instrmentName=instrmentName;
}
public Instrument(){

}

public void play(){
System.out.println(instrmentName+"play ");
}
}
}


／／／／／／／下面是Dog类
package bitch;

public class Dog extends Pets{
public Dog(String dogName){
// 调用父类的构造方法
super(dogName);
}
//覆盖父类的eat方法
public void eat(){
System.out.println(super.getPetsName()+"eat dogfoods");
}

}
／／／／／／／下面是cobaya类
package bitch;

public class Cobaya extends Pets {
public Cobaya(String cobayaName){
//diaoyong fulei de gouzaofangfa
super(cobayaName);
}
// cover father's the way of eating
public void eat(){
System.out.println(super.getPetsName()+"eating vagetable");
}

}
／／／／／／下面是pettest类
package bitch;

public class PetsTest {
public void testEat(Pets pets){
pets.eat();
}

public static void main(String[] args) {
// TODO Auto-generated method stub
PetsTest test=new PetsTest();
test.testEat(new Dog("jiwawa"));
test.testEat(new Cobaya("helanzhu"));

}

}

[loveypv520]

书上的提示是 ：如果我们再添加其他的宠物，比方说乌龟，我们不需要修改PetTest类的testPlay方法，直接在main方法中创建无归的对象即可

[qq_34729883]

几个意思？？？

[loveypv520]

初学发的，想给自己两巴掌