JAVA中的final关键字

/*
final class Demo
{
    void show()
    {}
}

//被final修饰的类不能被继承
class SubDemo extends Demo
{
    
}
*/
class Demo
{
    final int x = 3;
    final void show1()
    {}
    void show2()
    {
        final int y = 4;
        //y = 9;    //invalid
    }
}
class SubDemo extends Demo
{
    
    //void show1()
    //{} //无法被复写
    void show2()
    {}
    
}
class FinalDemo
{
    public static void main(String[] args)
    {
        System.out.println("Hello world!");
    }
}