When handling key input, I'm getting a negative timeout value in my thread. What's going on?

Question

So I'm programming a game using Swing and AWT and I'm getting a weird error. As I check for input in my MenuState, which is just my Menu screen, it is telling me that the timeout value in my game loop.

MenuState.java:

package GameState;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;

import Handlers.MyInput;
import TileMap.Background;

public class MenuState extends GameState {

    private Background bg;

    private int currentOption = 0;
    private String [] options = {
            "Start",
            "Help",
            "Quit"
    };

    private Color titleColor;
    private Font titleFont;

    private Font font;

    MenuState(GameStateManager gsm) {
        super(gsm);

        try {
            bg = new Background("/Backgrounds/Menu.gif", 1);
            bg.setVector(-0.1, 0);

            titleColor = new Color(128, 0, 0);
            titleFont = new Font("Jokerman", Font.PLAIN, 22);
            font = new Font("Times New Roman", Font.PLAIN, 12);
        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    public void update() {
        bg.update();
        handleInput();
    }

    public void draw(Graphics2D g) {

        bg.draw(g);

        //draw title
        g.setColor(titleColor);
        g.setFont(titleFont);
        g.drawString("Suddenly, Cold Pizza", 55, 70);

        g.setFont(font);
        for(int i = 0; i < options.length; i++) {
            if(i == currentOption) {
                g.setColor(Color.BLACK);
            } else {
                g.setColor(Color.RED);
            }
            g.drawString(options[i], 145, 140 + i * 15);
        }
    }

    public void init() {

    }

    private void select() {
        switch (currentOption) {
        case 0: 
            //start
            break;
        case 1:
            //help
            break;
        case 2: 
            //close
            System.exit(0);
        }
    }

    public void handleInput() {
        if(MyInput.isPressed(MyInput.BUTTON6)) {
            select();
        } else if(MyInput.isPressed(MyInput.BUTTON2)) {
            if(currentOption > 0) {
                currentOption--;
            }
        } else if(MyInput.isPressed(MyInput.BUTTON4)) {
            if(currentOption < options.length - 1) {
                currentOption++;
            }   
        }
    }

}

And then the function that contains my game loop:

GamePanel.java:

public void run() {
    init();

    long start;
    long elapsed;
    long wait;
    boolean first = true; 

    //game loop
    while(isRunning) {

        //start time
        start = System.nanoTime();

        update();
        draw();
        drawToScreen();

        //time elapsed
        elapsed = System.nanoTime() - start;

        //frame wait
        wait = targetTime - elapsed / 1000000;

        if(wait < 0) {
            wait = wait + 20;
        }

        try {
            Thread.sleep(wait);
        } catch(Exception e) {
            e.printStackTrace();
        }
    }
}

I'm getting the error in the Thread.sleep(wait). It says I have a negative value for wait, but in debugging, the value never appears to be negative.

If you need any more information, let me know and I'll post it.

Answer 1

The simplest solution is to guarantee that wait >= 0. Instead of adding 20 to it if it's not, why not just set it to 0?

A wait value of -8400 makes sense, on some frame you may take much longer in one of your update functions so elapsed time is much larger than your target time. I don't think it's an error in your calculations.