Why my contains and replace method doesn't work right?

Question

I was trying to make something then i couldn't write an if method with contains and replace method. What was i missing?

   import java.util.Scanner;
public class replacesomething
{
    public static void main(String[] args)
    {
        Scanner cumle = new Scanner(System.in);
        System.out.println("Enter the sentence u want to replace ");
        String str1 = cumle.next();
        if (str1.contains("replace"))
        {
            str1.replace("replace", "Hi");
            System.out.println("Replaced Sentence: " + str1);
        }
        else
        {
            System.out.println("Sentence doesn't contains that...");
        }

    }

}

Answer 1

Change the replace method call to:

str1 = str1.replace("replace", "Hi");

Since String are immutable, you need to reassign the result back to str1. It doesn't perform in-place replacement, rather it constructs and returns a new String object. the original String is unmodified.