public void speak(){ 

        System.out.print("Pet");   

    } 

} 

public class Cat extends Pet{ 

    public void speak(){ System.out.print("Cat")；

    } 

} public class Dog extends Pet{ 

    public void speak(){ System.out.print("Dog");    

} 

} 执行代码 

Pet[] p= {new Cat (),new Dog(),new Pet()}; 

for (int i=0;i<p.length;i++)  {

    p[i] .speak()；  

}

class Cat {

    Cat(int c) {

        System.out.print("cat" + c + " ");

    }

}

class SubCat extends Cat {

    SubCat(int c) {

        super(5);

        System.out.print("cable");

    }．

    SubCat() { this (4)； }

public static void main (String [] args) { SubCat s= new SubCat();//调用无参的 } } 结果为：

public static void main(String[] args){ 

    int a = 1; if(a < 1){ System.out.println(a); 

    }

    else{ 

        System.out.println(“a”); 

    } 

}

public class Scope {

    private int i;

    public static void main(String argv[]) {

        Scope s = new Scope();

        s.amethod();

    }

    public static void amethod() {

        System.out.println(i);

    }

}

public static void main(String args[]){ 

    SubClass ref1 = new SubClass (); SubClass ref2 = new SubClass (); System.out.println(ref1.add(ref2)); 

    }

}class Aclass｛ 

private int x; Aclass (int x){ this.x = x; 

    } 

}class SubClass extends Aclass｛

SubClass(int x){ 

    super(x); 

}

int add (Aclass ref){

    return x+ref.x ; 

    }

}