子类：
public class teacher extends stu{}
父类
public class stu {public String name="111";public void say(){System.out.println("shuohua");}
}
使用
public class Main
{public static void main(String[] args){teacher s=new teacher();s.say();System.out.println(s.name);}}
ctrl+h(看树结构，Java中所有的类都继承object类)
