这道Java题怎么做

创建类A1，实现构造方法中输出This is A;创建A1的子类B1，实现构造方法中输出This is B;创建B1的子类C1，实现构造方法中输出This is C。

public class A1 {
    public A1() {
        System.out.println("This is A");
    }
}
class B1 extends A1{
    public B1() {
        System.out.println("This is B");
    }
}
class C1 extends B1{
    public C1() {
        System.out.println("This is C");
    }
}