Here is my Code:

    //Gwendolyn Leister - Pong Game
    //Hit the ball with the paddle by moving the mouse left and right 
    //Each time you hit the paddle, your score goes up

    //Many thanks to the two forums that helped me: 
    //https://forum.processing.org/two/discussion/23862/subclass-won-t-display-or-move-help#latest
    //https://forum.processing.org/two/discussion/23842/myclass-move-does-not-exist-but-it-does#latest


    //Global Variables
    boolean gameStart = false;

    //Declare Fonts
    PFont myFont;
    PFont myFont2;

    final GamePiece Ball = new Ball();
    final GamePiece Paddle = new Paddle();

    void setup () {
      size(800, 800);
      smooth();
      background(0);
      myFont = loadFont("AnonymousPro-30.vlw"); //smaller text font
      myFont2 = loadFont("AnonymousPro-80.vlw"); //larger title font
    } 

    void draw() {

      background (#0A141F);

      //Layout
      rectMode(CORNER);
      fill(#CBFEFF);
      noStroke();
      rect(0, 640, 800, 260);
      stroke(255);
      fill(#CBFEFF);
      strokeWeight(10);
      line(0, 640, 800, 640);
      fill(#0A141F);
      rect(200, 700, 400, 160);

      //score text 
      textFont(myFont);
      textAlign(RIGHT);
      textSize(20);
      text("Score:", 70, 25);

      //display classes
      Ball.display();
      Paddle.display();

      if (gameStart) { //if the user hits enter to start game and allow subclasses to move/bounce
        Ball.move();
        Ball.bounce();
        Paddle.move();
      } else {  //when enter is not pressed or if it is pressed twice, it will pause the game

        textAlign(CENTER);
        textFont(myFont2);
        textSize(80);
        text("P O N G", 400, 100);
        textSize(20);
        text("press enter to start", 400, 600);
        text("move mouse horizontally to control the", 400, 140);
        text("paddle and to bounce the ball off of", 400, 162);
      }
    }



    // Resource used: https://processing.org/tutorials/interactivity/
    void keyPressed() { //if enter is pressed then the game starts {
      if (keyCode == ENTER) {
        gameStart = !gameStart;
      } else {
      }
    }

    abstract class GamePiece {
      //ball variables
      int rad = 15;
      float xPos=width/2;
      float yPos=height/2;
      float Speed = 6; 
      float xDirection = -2;
      float yDirection = -1;

      int score = 0;//call booleans
      boolean mouseMoved;
      boolean overPaddle = false;
      boolean locked = false;
      float dx=0;

      //paddle variables
      int px=mouseX;
      int py=550;
      int pw=100;
      int ph=30;
      int pSpeed = 5;

      int pDistance = 250; // paddle dis


      //calls
      abstract void move(); 
      abstract void display();
      abstract void bounce();
    }


    class Ball extends GamePiece {
      //Resource used: https://processing.org/examples/bounce.html


      int rad = 15;
      float xPos=width/2;
      float yPos=height/2;
      float Speed = 5;
      float xDirection = -2;
      float yDirection = -1;

      Ball() {
        super();
      }

      void display() {
        stroke(255);
        strokeWeight(3);
        fill(#FCE1BD);
        frameRate(30);
        ellipseMode(RADIUS);
        ellipse(xPos, yPos, rad, rad);
      }
      void move() { // ball position change
        xPos=xPos+Speed*xDirection;
        yPos=yPos+Speed*yDirection;
      }
      void bounce() { //https://processing.org/examples/bounce.html

        if (yPos - rad < py + ph/2) { // bounce ball off of paddle
          yDirection = -yDirection;  // when i apply this, then the ball acts crazy

          if (xPos>(width-rad)) { //bounce right side
            xPos = width-rad;
            xDirection=-xDirection;
          }
          if (xPos< rad) { //bounce left side
            xPos = rad;
            xDirection=-xDirection;
          }
          if (yPos<rad) { //bounce top side
            yPos=rad;
            yDirection=-yDirection;
          }

          if (yPos>800) { //falls below screen and relocates ball to inside the frame
            yDirection = -1;
            xPos=width/2;
            yPos=height/2;
          }
        }
      }
    }

    class Paddle extends GamePiece {

      Paddle () {
        super();
      }

      void display() {
        rectMode(CENTER);
        fill(#CBFEFF);
        stroke(255);
        strokeWeight(5);
        rect(mouseX, py, pw, ph);  //moves paddle with mouse
      }

      void move() {
      }

      void bounce () { 
      }
    }

My code:

float ballSpeed=5;
float PaddleSpeed=6;
gamePieces paddle;
gamePieces ball;
boolean mousePressed = false;


//paddle p1;

int playerscore = 0;
int cpuscore = 0;
int lastlevel = 3;
boolean keypress = false;
boolean endgame = false;

void setup () {
  size(800, 800);
  smooth();
  background(255);
  ball = new ball();
}

void draw() {
  //table
  background(0);


  //displays

  ball.display();
  if (endgame) {
    textSize(30);
    textAlign(CENTER);
    fill (255);
    text("Click to Start", 400, 100);
  } else {
    if (mousePressed == true) {
      ball.move();
      //paddle.moveX(moveX);

      //paddle.intersectTop(ball);
    }
  }
}

Ball clas (was in a separate tab)

class ball extends gamePieces {

  // processing.org/examples/bounce.html
  int rad = 20;
  float xpos, ypos;

  float xspeed = 2.6;
  float yspeed = 2.5;

  int xdirection = 1;
  int ydirection = 1;


  ball() {
    super();
  }

  void display() {
    stroke(255);
    strokeWeight(3);
    fill(#FFFEE8);
    frameRate(30);
    ellipseMode(RADIUS);
    ellipse(xpos, ypos, rad, rad);
  }

  void move () {
    xpos = width/2;
    ypos = height/2;

    xpos = xpos + (xspeed * xdirection);
    ypos=+ ypos + (yspeed * ydirection);

    if (xpos > width-rad || ypos < rad) {
      xdirection *= -1;
    }
    if (ypos > height-rad || ypos < rad) {
      ydirection *= -1;
    }
  }
}

float x = 300;
float y = 300;
float velocityX = 2;
float velocityY = 3;
////////////////////
float paddleY;
float paddleX = 20;
float paddleW = 20;
float paddleH = 100;
////////////////////
float ai;
float paddleY2 = 20;
float paddleX2 = 570;
float paddleW2 = 20;
float paddleH2 = 100;

void setup() {
  size(600,680);
}

void draw() {
  x += velocityX;
  y += velocityY;

  background(20);  
  noStroke();
  fill(255);
  rect(x,y,20,20);
  rect(paddleX,paddleY,paddleW,paddleH);
  rect(paddleX2,ai,paddleW2,paddleH2);
  fill(100);
  strokeWeight(2);
  stroke(255);
  rect(-1,0,601,80);
  rect(-1,600,601,80);
  //println(player);
  //println(ballY);
  ai = y-50;
  //paddleY = y-50;

  if (x <= -20) {
    x = 100;
    y = 100;
  } else if (x >= 600) {
    x = 100;
    y = 100;
  }

  /*if (x > 580 || x < 0) {
    velocityX *= -1;
  }*/
  if (y > 580 || y < 80) {
    velocityY *= -1;
  }

  if (x - 20/2 < paddleX + paddleW/2 && y - paddleH/2 < paddleY + 100/2 && y + 100/2 > paddleY - paddleH/2) {
    velocityX /= -1;

  }

  if (x + 20/2 > paddleX2 - paddleW2/2 && y - paddleH2/2 < paddleY + 100/2 && y + 100/2 > paddleY2 - paddleH2/2) {
    velocityX /= -1;

  }
}

 bonuses_array = [
   { name: "Paddle_size +", type: "Bonus", status: false, effect: addPSize(), duration: 30, graphic: Paddle_size_plus()},
   { name: "Paddle_speed +", type: "Bonus", status: false, effect: addPSpeed(), duration: 30, graphic: Paddle_speed_plus()},
   { name: "Ball_speed -", type: "Bonus", status: false, effect: reduceBSpeed(), duration: 30, graphic: Ball_speed_minus()},
   { name: "Paddle_size -", type: "Malus", status: false, effect: reducePSize(), duration: 30, graphic: Paddle_size_minus()},
   { name: "Paddle_speed -", type: "Malus", status: false, effect: reducePSpeed(), duration: 30,graphic: Paddle_speed_minus()},
   { name: "Ball_speed +", type: "Malus", status: false, effect: addBSpeed(), duration: 30, graphic: Ball_speed_plus()},
   { name: "Ball_size -", type: "Malus", status: false, effect: reduceBSize(), duration: 30, graphic: Ball_size_minus()},
  ]

All the functions are defined somewhere else, and the thing i want to achieve is to be able to call bonuses_array[value].graphic(x, y). But it seems that the functions are not defined the right way... Can someone help me ? Thanks !! Ali

Now I was stuck in the how to generate a new ball and how to consider if the ball hit the paddle or paddles missed it.

Here are the questions: 1.How can I make relationship between the coordinate of the center of the paddle to the center of the ball? Should I add more conditions in the if block to change the speed of ball which it hits the paddles? 2.How can I generate a new ball when the both paddles missed the ball? Should I add a boolean named collision and assign it to true? And if it was false the program will generate a new ball? Was my method right or wrong? Could you guys give me some hints?

float ballX = 250;
float ballY = 250;
float ballSize = 20;
float ballSpeedX = 3;
float ballSpeedY = 8;
float ballGenSpeed = 3;

float borderTop = 25;
float borderBottom = 450;
float borderLeft = 0;
float borderRight = 450;

float paddleH = 10;
float paddleW = 100;
float paddleSpeed = 15;
float paddleX;

void setup()
{
  size(500, 500);
  background(0);
}

void draw()
{
  background(0);
  ballX += ballSpeedX;
  ballY += ballSpeedY;

  if (ballX < borderLeft || ballX > borderRight)
  {
    ballSpeedX *= -1;
  }
  if (ballY < borderTop+(paddleH*2) || ballY > borderBottom-paddleH)
  {
    ballSpeedY *= -1;
  }

  ellipse(ballX, ballY, ballSize, ballSize);

  boolean collision = true;



  if (!collision) {
    for (int i = 0; i<20; i++)
    {
      float theta = i/20 * 2 * PI;
      float ballDirectX = cos(theta)*ballGenSpeed;
      float ballDirectY = sin(theta)*ballGenSpeed;
      ellipse(ballDirectX, ballDirectY, ballSize, ballSize);
    }
  }

  rect(mouseX, borderTop, paddleW, paddleH);
  rect(paddleX, borderBottom, paddleW, paddleH);
  if (key == CODED) {
    if (keyCode == LEFT && keyPressed) {
      paddleX -= paddleSpeed;
    } else if (keyCode == RIGHT && keyPressed) {
      paddleX += paddleSpeed;
    }
  }
}