Guess the Number

The computer thinks of a number and you try to find it. This is the first project where the program asks you something and does different things depending on the answer.

a guessing game asking for numbers and giving hints

The whole thing is one class, and it needs no files at all.

Step 1: Ask a question

ask() puts a box at the bottom of the stage, exactly where Scratch puts it, and collects what you type until you press Enter. getAnswer() gives you back what was typed.

ask [Guess a number between 1 and 10] and wait

Start with this much:

import org.openpatch.scratch.*;
 
public class GuessStage extends Stage {
  private int secret = Random.randomInt(1, 10);
 
  public GuessStage() {
    super(500, 300);
    this.addBackdrop("background");
    this.ask("Guess a number between 1 and 10");
  }
}

Step 2: One important difference from Scratch

In Scratch, ask and wait stops the script until you answer. In Java it does not: run() keeps being called about 60 times a second while the question sits on screen.

So instead of waiting, you check whether a question is still open:

public void run() {
  if (this.isAsking()) {
    return;      // the question is still on screen, come back next time
  }
  // there is an answer waiting
}

That return is doing the job Scratch's "wait" does for you.

getAnswer() always gives you text, even when someone types a number, so it has to be turned into a number first. If they typed something that is not a number at all, Integer.parseInt fails, and the catch block deals with it.

Here is the finished class:

import org.openpatch.scratch.*;
 
public class GuessStage extends Stage {
  private int secret = Random.randomInt(1, 10);
  private int tries = 0;
  private boolean solved = false;
  private Text hint = new Text();
 
  public GuessStage() {
    super(500, 300);
    this.addBackdrop("background");
 
    this.hint.setPosition(0, 60);
    this.hint.setTextSize(20);
    this.add(this.hint);
 
    Sprite wizard = new Sprite();
    wizard.addCostume("alienBlue_front");
    wizard.setSize(40);
    wizard.setY(-40);
    this.add(wizard);
 
    this.ask("Guess a number between 1 and 10");
  }
 
  public void run() {
    if (this.solved || this.isAsking()) {
      return;
    }
 
    int guess = 0;
    try {
      guess = Integer.parseInt(this.getAnswer().trim());
    } catch (NumberFormatException e) {
      this.hint.showText("That is not a number. Try again!");
      this.ask("Guess a number between 1 and 10");
      return;
    }
 
    this.tries = this.tries + 1;
 
    if (guess < this.secret) {
      this.hint.showText(guess + " is too small.");
      this.ask("Guess again");
    } else if (guess > this.secret) {
      this.hint.showText(guess + " is too big.");
      this.ask("Guess again");
    } else {
      this.hint.showText("Yes! It was " + this.secret + ", in " + this.tries + " tries.");
      this.solved = true;
    }
  }
 
  public static void main(String[] args) {
    new GuessStage();
  }
}

The solved variable is easy to forget, and leaving it out gives a strange bug. Once the number is guessed, no new question is asked, so isAsking() stays false — and run() happily counts the same answer again on every single frame. The number of tries races upwards. solved is what stops it.

The finished project

If something will not run, you can compare against the finished version. It needs no assets, only the library itself.

⏬Project: Guess the Number 100%

Things to try

Give the player only five tries.
Let the wizard say() the hints instead of writing them at the top.
Ask for a name first and use it in the hints.

Guess the Number

Step 1: Ask a question

Step 2: One important difference from Scratch

Step 3: React to the answer

The finished project

Things to try