构造方法是一种特殊的方法，它的继承规则比较简单，而且与普通方法有较大的区别
1 无参数构造方法的构造方法示例
class hasConstructor{
protected int x=100;
public void showMsg(){
System.out.println("this is a method in ancesstor");
}
public hasConstructor(){
System.out.println("this is a constructor in ancestor without parameter");
}
public hasConstructor(int ix){
System.out.println("this is a constructor in ancestor with parameter");
}
}