Java Lambda Expressions for repeated String concatenation

The following is an exercise from a lambda expressions tutorial, but I’m kinda stuck at how to do it, since I don’t have much experience with lambda expressions.

I have a functional interface Greeter which has the method greet(Integer n). Now I should write a test to learn how to write lambda expressions. The first test was given:

@Test
void test0() {
  Greeter greeter = (Integer n) -> { return "Hello World!"; };
  assertThat(greeter.greet(1)).isEqualTo("Hello World!");
}

Now, the second test should test that "Hello World! Hello World! Hello World!" is returned when n = 3.

@Test
void test1() {
  Greeter greeter = null;
  assertThat(greeter.greet(3)).isEqualTo("Hello World! Hello World! Hello World!");
}

How do I concatenate the "Hello World!" with a lambda expression (not a stream)?

>Solution :

You might go like this

Greeter greeter = (Integer n) -> { 
     String s = "Hello World!";
     for(int i = 1; i < n; i++){
       s = " " + s;
     }
     return s;
}