方法的重写
class number {void num(){ System.out.println("大家好");} void num(int x,int y){ System.out.println("两个数是:"+x+" "+y);}}class sum extends number {int z = 10 ;//在子类重写父类，子类将覆盖父类。 void num(int x,int y) //子类的继承权限一定要大于等于父类的权限{ super.num(20,30);//我们可以通过关键字super去重写父类。用super.调用父类的num方法。 System.out.println("x="+x+" y="+y+" z="+z);}}class test {public static void main(String[]args){number objnum = new number();sum objsum = new sum();objnum.num();//objnum.num(20,30);objsum.num(30,40);}}