Help with pong collision

Question

I am working on a pong-like game for a project... and i am having some trouble with collision checks... again.
Here is our code so far, the problem is that the ball seems to be stopping completely when it is aligned with a paddle on the Y axis (even if it is at the center of the screen)
import java.applet.*;
import java.awt.*;
import java.util.*;
import java.awt.event.*;
public class TestApplet extends Applet implements Runnable
    //Paddle dimensions
    int PaddleHeight = 50;
    int PaddleWidth = 10;
    //Other variables
    boolean isStop = true;
    int[] theKeys = new int[256]; //Array with one element representing each key
    Random Rand = new Random();
    int bounces = 0;
    boolean isAI2 = false;
    boolean isAI1 = false;
    ArrayList <Ball> TheBalls = new ArrayList <Ball>();
    Paddle[] ThePaddles = new Paddle[2];
    //Player scores
    int Score1 = 0;
    int Score2 = 0;
    private Image dblimage;
    private Graphics dbg;
    public void init()
        //Set Background color to black
        setBackground(Color.black);
    public void start()
        //Define new thread
        Thread th = new Thread(this);
        //Start the new thread
        th.start();
        for(int z=0; z<256; z++)
            theKeys[z] = 0; //Set all keys to default position (released)
        enableEvents(AWTEvent.KEY_EVENT_MASK);
        ThePaddles[0]=(new Paddle(true, PaddleHeight, PaddleWidth, 10, this.getWidth(), this.getHeight(), 'w', 's'));
        ThePaddles[1]=(new Paddle(false, PaddleHeight, PaddleWidth, 10, this.getWidth(), this.getHeight(), '8', '5'));
        TheBalls.add(new Ball(this.getHeight(), this.getWidth()));
        TheBalls.get(0).AddPaddle(ThePaddles[0]);
        TheBalls.get(0).AddPaddle(ThePaddles[1]);
    public void run ()
        //Minimize thread priority
        Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
        while (true)
            for(int i=0; i<ThePaddles.length; i++)
                if(isKeyPress(87))
                    ThePaddles.Move(1);
else if(isKeyPress(83))
ThePaddles[i].Move(-1);
if(isKeyPress(32))
for(int x=0; x < TheBalls.size(); x++)
TheBalls.get(x).Start();
isStop = false;
bounces = 0;
for(int i=0; i<TheBalls.size(); i++)
TheBalls.get(i).Move();
String scored = TheBalls.get(i).IsScore();
if(scored == "Player 1")
Score1++;
break;
else if(scored == "Player 2")
Score2++;
break;
repaint();
try
Thread.sleep (20);
catch (InterruptedException ex)
// do nothing
Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
public void paint(Graphics g)
//set color
g.setColor(Color.green);
for(Ball temp : TheBalls)
int[] tempfo = temp.BallInfo();
g.fillOval(tempfo[0], tempfo[1], tempfo[2], tempfo[3]);
for(Paddle temp: ThePaddles)
int[] PadTemp = temp.PaddleData();
g.fillRect(PadTemp[0], PadTemp[1], PadTemp[2], PadTemp[3]);
//paint player 1 score
g.drawString("Player 1 score: "+Score1, 10, 50);
//paint player 2 score
g.drawString("Player 2 score: "+Score2, 400, 50);
//paint current bounce count
g.drawString("Bounces: "+bounces, 250, 50);
g.drawString(""+ThePaddles[0].GetUp(), 100, 100);
g.drawString(""+ThePaddles[0].GetDown(), 100, 400);
g.drawString(""+ThePaddles[1].GetUp(), 200, 100);
g.drawString(""+ThePaddles[1].GetDown(), 200, 400);
g.drawString(""+TheBalls.get(0).Collide(), 250, 250);
g.drawLine(ThePaddles[0].getX(), ThePaddles[0].GetTop(), ThePaddles[0].getX()-500, ThePaddles[0].GetTop());
public void update (Graphics g)
// initialize buffer
if (dblimage == null)
dblimage = createImage (this.getSize().width, this.getSize().height);
dbg = dblimage.getGraphics ();
// clear screen in background
dbg.setColor (getBackground ());
dbg.fillRect (0, 0, this.getSize().width, this.getSize().height);
// draw elements in background
dbg.setColor (getForeground());
paint (dbg);
// draw image on the screen
g.drawImage (dblimage, 0, 0, this);
public void processKeyEvent(KeyEvent ev)
int keycode = (ev.getKeyCode()&0xff);
if (ev.getID() == KeyEvent.KEY_PRESSED)
theKeys[keycode] = 1; //1 Represents key is pressed
else if (ev.getID() == KeyEvent.KEY_RELEASED)
theKeys[keycode] = 0; //0 Represents key is not pressed
repaint();
//Checks if a given key is pressed
public boolean isKeyPress(int theKey)
return (theKeys[theKey] != 0);
//Checks if a given key is released
public boolean isKeyRel(int theKey)
return(theKeys[theKey] == 0);
class Paddle
private int
XPos,
YPos,
Width,
Height,
Speed,
AppletHeight,
AppletWidth,
Down,
Up;
boolean
LeftSide;
public Paddle(boolean LeftSide, int Height, int Width, int Speed, int AppletWidth, int AppletHeight, char Up, char Down)
this.AppletHeight = AppletHeight;
this.AppletWidth = AppletWidth;
YPos = AppletHeight/2;
this.Height = Height;
this.Width = Width;
this.Speed = Speed;
this.LeftSide = LeftSide;
if(LeftSide)
this.XPos = 15;
else
this.XPos = AppletWidth-25;
Character UpChar = new Character(Up);
Character DownChar = new Character(Down);
this.Up = UpChar.charValue();
this.Down = DownChar.charValue();
public void Move(int x)
if(x > 0)
YPos -= Speed;
else
YPos += Speed;
public int GetTop()
return YPos - Height/2;
public int GetBottom()
return YPos + Height/2;
public int GetUp()
return Up;
public int GetDown()
return Down;
public int getX()
return XPos;
public int getY()
return YPos;
public int GetHeight()
return Height;
public int GetWidth()
return Width;
public int[] PaddleData()
if(LeftSide)
return new int[]{XPos+Width/2, YPos-Height/2, Width, Height};
return new int[]{XPos-Width/2, YPos-Height/2, Width, Height};
class Ball
private int
XPos,
XSpeed,
YPos,
YSpeed,
Radius,
MaxSpeed,
Height,
Width;
private boolean
IsStill;
private ArrayList <Paddle>
ThePaddles=new ArrayList <Paddle>();
private Random Rand=new Random();
public Ball(int Width, int Height)
this.ThePaddles=ThePaddles;
this.Height=Height;
this.Width=Width;
XPos=Width/2;
YPos=Height/2;
IsStill=true;
MaxSpeed=9;
Radius=10;
ChangeAngle();
public void AddPaddle(Paddle temp)
ThePaddles.add(temp);
public int[] BallInfo()
return new int[]{XPos-Radius, YPos-Radius, 2*Radius, 2*Radius};
public void Start()
IsStill = false;
public int getX()
return XPos;
public int getY()
return YPos;
public int getRad()
return Radius;
public void RevX()
XSpeed *= -1;
public int getXSp()
return XSpeed;
public int getYSp()
return YSpeed;
public boolean isNeg()
if(XSpeed < 0)
return true;
return false;
//Generates a random trajectory for the ball
public void ChangeAngle()
int Num, Opp;
Num= Rand.nextInt(MaxSpeed)+1;
Opp = MaxSpeed-Num;
XSpeed = ((XSpeed>0)?1:-1)*Num;
YSpeed = ((Rand.nextInt(2)==0)?1:-1)*Opp;
public boolean Collide()
boolean collid=false;
for(Paddle i: ThePaddles)
if(YPos >= i.GetTop() && YPos <= i.GetBottom())
if(i.LeftSide)
collid = (((XPos - Radius) <= (i.getX() + i.GetWidth())));
if(!collid)
collid = (((XPos + Radius) >= (i.getX() - i.GetWidth())));
if(!collid)
collid = ((YPos<=0 && YSpeed < 0) || (YPos>=Height && YSpeed > 0));
return collid;
public String IsScore()
if(XPos >= Width)
XPos = Width/2;
YPos = Height/2;
IsStill = true;
return "Player 1";
if(XPos <= 0)
XPos = Width/2;
YPos = Height/2;
IsStill = true;
return "Player 2";
return "";
public void Move()
boolean temp = false;
for(int i=0; i<=Math.abs(XSpeed); i++)
if((Collide()) && !temp)
RevX();
ChangeAngle();
temp = true;
break;
XPos = ((XSpeed>0)?XPos+1:XPos-1);
temp = false;
for(int i=0; i<=Math.abs(YSpeed); i++)
if((Collide()) && !temp)
YSpeed *= -1;
temp = true;
break;
YPos = ((YSpeed>0)?YPos+1:YPos-1);

Answer 1

    public boolean Collide()
        boolean collid=false;
        for(Paddle i: ThePaddles)
            if(YPos >= i.GetTop() && YPos <= i.GetBottom())
                if(i.LeftSide)
                    collid = (((XPos - Radius) <= (i.getX() + i.GetWidth())));
//                if(!collid)
                else
                    collid = (((XPos + Radius) >= (i.getX()/* - i.GetWidth()*/)));