How do you prompt a user for an input in java

Question

So I just started learning Java, its literally like my 1st day and I wanted to try to make a coinflip game. I already know a decent amount of JavaScript and so i was trying to apply that knowledge to Java. So everything has been working so far except one thing: Prompting a user for a choice.

So read online that i have to import a scanner so i did that as you can see from my code. I also tried some code where you can have the user import a string but you can see a bit later in my program I change the variable userChoice into a number. So basically I just need help with this.

If there is some way to have a variable type that can store both numbers or strings that would be best. But I'm totally open to other ways of doing this!

Here is the code:

package test;
import java.util.Scanner;

public class testclass {
    
  public static void main(String[] args) {

    // TODO Auto-generated method stub
    System.out.println("hi");
    int bob;
    bob = (int) Math.floor(Math.random()*2);
    System.out.println(bob);
            
    System.out.println("Enter heads or tails?");
    System.out.println("You entered "+ userChoice);
              
    if (bob == 0) {
      System.out.println("Computer flipped heads"); 
    } else {
      System.out.println("Computer flipped tails");
    }
              
    if(userChoice == "Heads") {
      userChoice = 0;
    } else {
      userChoice = 1;
    }
              
    if (userChoice == bob) {
       System.out.println("You win!");
    } else {
       System.out.println("Sorry you lost!")
    }
              
  }
}

Answer 1

Use a scanner, as you said:

Scanner in = new Scanner(System.in);

Then, prompt the user to enter something in:

String userChoice = in.nextLine();

Also, when you compared strings:

if(userChoice == "Heads") {...

that's bad to do for none-primitive objects. It's best to only use the == to compare values that are ints or enums. If you compare a String like this, it won't work, because it's checking if the objects are the same. Instead, compare like this:

if(userChoice.equals("Heads")) {...

Also, to convert to an int (NOTE: You can't convert one type of object to another that aren't related in any way! You'll have to create a new object if you're wanting to do that), do this:

int myInt = Integer.parseInt(myString); // NOTE: Can throw NumberFormatException if non-number character is found.

So your program should look somewhat like:

    package test;
    import java.util.Scanner;

    public class testclass {

        public static void main(String[] args) {
            //System.out.println("hi");
            Scanner in = new Scanner(System.in);
            int bob;
            int userChoice;
            String input;
            bob = (int) Math.floor(Math.random()*2);
            System.out.println(bob);

            System.out.println("Enter heads or tails?");
            input = in.nextLine(); // waits for user to press enter.
            System.out.println("You entered "+ input);

            if (bob == 0) {
                System.out.println("Computer flipped heads"); 
            }

            else {
                System.out.println("Computer flipped tails");
            }

            if(input.equals("Heads")) {
                userChoice = 0;
            }
            else {
                userChoice = 1;
            }

            if (userChoice == bob) {
                System.out.println("You win!");
            }
            else {
                System.out.println("Sorry you lost!");
            }

            in.close(); // IMPORTANT to prevent memory leaks
        }
    }