Java strings comparison results in different boolean values

Question

Can anyone please explain, why the outputs are printing two different boolean values. why aren't strings being compared not equal in this case. while simply comparing two strings with '==' operator does compare the strings. For example, System.out.print("paper" == "paper") prints true. Thanks in advance. :)

package my_pack;

    import java.util.Objects;
    import java.util.Random;
    import java.util.Scanner;


    public class game {
        public static void main(String[] args) {
            //get the user input get_input()
            Scanner scn = new Scanner(System.in);
            System.out.println("Rock Paper or Scissor? Enter Your choice: ");
            String user_choice = scn.nextLine();
            user_choice = user_choice.toLowerCase();

            //get the random number
            Random rand = new Random();
            int random_num = rand.nextInt(3) + 1;

            //assign the number to specified method
            String comp_choice ="";
            switch (random_num){
                case 1:
                    comp_choice = "rock";
                    break;
                case 2:
                    comp_choice = "paper";
                    break;
                case 3:
                    comp_choice = "scissor";
                    break;
            }
            System.out.println(comp_choice);
            System.out.println(user_choice == comp_choice); //paper == paper (false)
            System.out.println(Objects.equals(user_choice, comp_choice)); //paper == paper (true)

        }

    }

Downvoted for lack of prior research. – GhostCat Nov 07 '17 at 04:47 — GhostCat, Nov 07 '17 at 04:47

score 1 · Answer 1 · edited Nov 07 '17 at 06:34

If you came from c++, it will be easier to think as compare by reference(==) and compare by value(equals) .

When you compare two Strings using ==, you are comparing two objects and their references, not their values. When you compare two string literals, such as "paper" == "paper", they are pointing to the same block of memory, therefore the line returns true.

Instead of ==, using yourString.equals(stringToCompare) or .equalsIgnoreCase to ignore differences in capitalization.

  System.out.println("RANDOM CHOICE: " + comp_choice); //display user and comp choice
  System.out.println("USER CHOICE: " + user_choice); 
  System.out.println("USER = COMP? " + user_choice.equalsIgnoreCase(comp_choice));  //compare both choices

I quite did not get what you meant by compare by reference and compare by value. Can you provide me some references? — Bigyan Karki, Nov 07 '17 at 04:40

Java strings comparison results in different boolean values

1 Answers1