java 子类与父类继承关系

People.java

public class People {
    int age,leg = 2,hand = 2;
    protected void showPeopleMess() {
       System.out.printf("%d岁，%d只脚,%d只手\t",age,leg,hand);
    }
}

Student.java

public class Student extends People {
   int number;
   void tellNumber() {
       System.out.printf("学号:%d\t",number);
   }
   int add(int x,int y) {
      return x+y;
   }
} 

UniverStudent.java

public class UniverStudent extends Student {
   int multi(int x,int y) {
      return x*y;
   }
}

Example5_1.java

public class Example5_1 {
   public static void main(String args[]) {
      Student zhang = new Student();
      zhang.age = 17;           //访问继承的成员变量
      zhang.number=100101;
      zhang.showPeopleMess();  //调用继承的方法
      zhang.tellNumber();
      int x=9,y=29;
      System.out.print("会做加法:");
      int result=zhang.add(x,y);
      System.out.printf("%d+%d=%d\n",x,y,result);
      UniverStudent geng = new UniverStudent();
      geng.age = 21;          //访问继承的成员变量
      geng.number=6609;
      geng.showPeopleMess();  //调用继承的方法
      geng.tellNumber();        //调用继承的方法
      System.out.print("会做加法:");
      result=geng.add(x,y);      //调用继承的方法
      System.out.printf("%d+%d=%d\t",x,y,result);
      System.out.print("会做乘法:");
      result=geng.multi(x,y);
      System.out.printf("%d×%d=%d\n",x,y,result);
   }
} 

注意：父类的私有变量、类不能够被继承