java - What is the purpose of concatenating a string and an integer?

Question

This method returns true if the number passed in contains a 1.

public boolean hasOne(int n) {
  return (n + "").contains("1");
}

What is the purpose of the + "" part? How does that make n a string? (.contains only works with Strings as far as I understand).

Answer 1

An int is a primitive. Adding a primitive to a string will perform an implicit conversion of that primitive to a String and add the two strings together. In this case, the int is converted and "" ( empty String ) is added,

That can be rewritten as:

return Integer.toString(n).contains("1");

or

return String.valueOf(n).contains("1");

or

return String.format("%d", n).contains("1");