如何转动物体并向相反方向移动？

Question

Considering out of bounds position is 6 and -6.

I want to make the ship turn around and move in the opposite direction.

This is the code I have.. It is still not working 100% how I want it. I am curious to see if anyone had any ideas how do improve. Here is the logic of my code.

//If the ship hits a boundary it turns around and moves in the opp.
//direction. To do this, the ship's velocty should be flipped from a 
//negative into a positive number, or from pos to neg if boundary
//is hit.

//if ship position is -5 at velocity -1 new ship pos is -6
//if ship position is -6 at velocity -1 new ship velocity is +1
//                                      new ship position is +5

Here is my code:

public void move() 
{
    position = velocity + position;

    if (position > 5)
    {
        velocity = -velocity;
    }
    else if (position < -5)
    {
        velocity = +velocity;
    }
}

Answer 1

You can do this:

public void move() 
    {
    //first check where the next move will be:
    if ((position + velocity) > 5 || (position + velocity) < -5){

        // Here we change direction (the velocity is multiplied for -1)
        velocity *= -1;

    }

    position += velocity;
}

Answer 2

The code velocity = +velocity; will not change a negative velocity into a positive velocity. What this will do is equivalent to multiplying velocity with +1 which does not change the sign.

To flip the sign of velocity when going out of bounds you need to always multiply -1 .

It's not very clear what the bounds are so below I assume that they are 6 and -6.

position += velocity;
//make sure the ship cannot go further than the bounds
//but also make sure that the ship doesn't stand still with large velocities
if (position > 6)
{
    velocity = -velocity;
    position = 6;
}
if (position < -6)
{
    velocity = -velocity;
    position = -6;
}

Answer 3

当它到达边界时，将速度乘以-1。

Answer 4

Firstly, your logic looks a bit flawed. If the position is -6 and the velocity is -1 , to start moving in the opposite direction, you new position should be -5 (and not +5 ) and the velocity +1 .

Also, you need to invert the sign of your velocity whenever your position hits the boundary conditions.

public void move() {
    if (Math.abs(position + velocity) > 5) { // Check for boundary conditions
        velocity *= -1;
    }
    position = position + velocity; // position += velocity;
}

Answer 5

If you want it to change direction you need to flip the sign. This is the same a * -1 or negating it.

public void move() {    
    // prevent it jumping through the wall.
    if (Math.abs(position + velocity) > 5)
        velocity = -velocity;

    position += velocity;
}