Question

I am coding a space invaders clone, I need the invaders to do their usual movement but pause for one second before moving again.

EG. Move 5 pixels, then wait, then move another 5 pixels.

The method called moveInvaders() is the method I want to make wait for 1000ms. Below is that such method.

private void moveInvaders() {
        if(direction == "right") {
        if(invaderGreenEight.getX() == 455 || invaderRedEight.getX() == 455 || invaderBlueEight.getX() == 455) {
            direction = "left"; // Change direction to left
        }
    } else {
        if(invaderGreenOne.getX() == 15 || invaderRedOne.getX() == 15 || invaderBlueOne.getX() == 15) {
            direction = "right"; // Change direction to right
        }
    }

    if(direction == "right") {
        // Move Green Invaders Right
        invaderGreenOne.moveX(1);
        invaderGreenTwo.moveX(1);
        invaderGreenThree.moveX(1);
        invaderGreenFour.moveX(1);
        invaderGreenFive.moveX(1);
        invaderGreenSix.moveX(1);
        invaderGreenSeven.moveX(1);
        invaderGreenEight.moveX(1);
        // Move Red Invaders Right
        invaderRedOne.moveX(1);
        invaderRedTwo.moveX(1);
        invaderRedThree.moveX(1);
        invaderRedFour.moveX(1);
        invaderRedFive.moveX(1);
        invaderRedSix.moveX(1);
        invaderRedSeven.moveX(1);
        invaderRedEight.moveX(1);
        // Move Blue Invaders Right
        invaderBlueOne.moveX(1);
        invaderBlueTwo.moveX(1);
        invaderBlueThree.moveX(1);
        invaderBlueFour.moveX(1);
        invaderBlueFive.moveX(1);
        invaderBlueSix.moveX(1);
        invaderBlueSeven.moveX(1);
        invaderBlueEight.moveX(1);
    }
    if(direction == "left") {
        // Move Green Invaders Left
        invaderGreenOne.moveX(-1);
        invaderGreenTwo.moveX(-1);
        invaderGreenThree.moveX(-1);
        invaderGreenFour.moveX(-1);
        invaderGreenFive.moveX(-1);
        invaderGreenSix.moveX(-1);
        invaderGreenSeven.moveX(-1);
        invaderGreenEight.moveX(-1);
        // Move Red Invaders Right
        invaderRedOne.moveX(-1);
        invaderRedTwo.moveX(-1);
        invaderRedThree.moveX(-1);
        invaderRedFour.moveX(-1);
        invaderRedFive.moveX(-1);
        invaderRedSix.moveX(-1);
        invaderRedSeven.moveX(-1);
        invaderRedEight.moveX(-1);
        // Move Blue Invaders Right
        invaderBlueOne.moveX(-1);
        invaderBlueTwo.moveX(-1);
        invaderBlueThree.moveX(-1);
        invaderBlueFour.moveX(-1);
        invaderBlueFive.moveX(-1);
        invaderBlueSix.moveX(-1);
        invaderBlueSeven.moveX(-1);
        invaderBlueEight.moveX(-1);
    }
}

The game is already a thread and the method in question is in the same class so issuing Thread.sleep(1000); just pauses the entire game for 1 second, but I just want the execution of one method to pause.

If you want more information I am more than happy to provide it.

GeissT

Answer 1

The moveInvaders() method should keep track of a member variable which stores the time the invaders were last moved (e.g. as a long number of milliseconds), this way, any time it is called it can check the value of that variable – if enough time has elapsed then the invaders can move, if not, then the method will simply return without doing anything. For example:

protected long invadersLastMovedMillis;

protected void moveInvaders() {
  long currentTime = System.currentTimeMillis();
  if ((invadersLastMovedMillis != 0)
      && ((currentTime - invadersLastMovedMillis) < 1000L)) {
    return; // No need to move them yet.
  }
  // March on, space invaders!
  invadersLastMovedMillis = currentTime;
}

You don’t want to actually cause the thread to sleep because the game will then become unresponsive!