Snake v0.1

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Snake extends JComponent
{
    private final static int ANCHO = 500, ALTO = 500, LADO = 10, VELO = 200;
    private float x, y, xf, yf;
    private float vx, vy;
    private boolean arriba, abajo, izquierda, derecha, teclaZ, teclaX, teclaC;
    private boolean pause;
    private static int score=0;

    public Snake()
    {
        setPreferredSize(new Dimension(ANCHO, ALTO));

        addKeyListener(new KeyAdapter() {
                public void keyPressed(KeyEvent e) {
                    actualiza(e.getKeyCode(), true);
                }

                public void keyReleased(KeyEvent e) {
                    actualiza(e.getKeyCode(), false);
                }

                private void actualiza(int keyCode, boolean pressed) {
                    switch (keyCode) {
                        case KeyEvent.VK_UP:
                            arriba = pressed;
                            break;

                        case KeyEvent.VK_DOWN:
                            abajo = pressed;
                            break;

                        case KeyEvent.VK_LEFT:
                            izquierda = pressed;
                            break;

                        case KeyEvent.VK_RIGHT:
                            derecha = pressed;
                            break;

                        case KeyEvent.VK_Z:
                            teclaZ = pressed;
                            break;

                        case KeyEvent.VK_X:
                            teclaX = pressed;
                            break;

                        case KeyEvent.VK_C:
                            teclaC = pressed;
                            break;
                    }
                }
            });
        setFocusable(true);
    }

    private float ajustar(float valor, float min, float max)
    {
        if (valor > max) return max;
        if (valor < min) return min;
        return valor;
    }

    private boolean colision(float x, float y, float xf, float yf)
    {
        int a, b, c, d;

        for( a = (int) x ; a<x+LADO ; a++ )
        {
            for( b = (int) y ; b<=y+LADO ; b++ )
            {
                for( c = (int) xf ; c<=xf+LADO ; c++ )
                {
                    for( d = (int) yf ; c<=yf+LADO ; c++ )
                    {
                        if( a==c && b==d ) return true;
                        //System.out.println( "("+a+","+b+")==("+c+","+d+")" );
                    }
                }
            }
        }

        return false;
    }

    public void paint(Graphics g) {

        // BOX
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, ANCHO, ALTO);

        // SCORE
        g.setColor(Color.BLACK);
        g.setFont( new Font("Serif", Font.BOLD, 20) );
        g.drawString( ""+score , 5, 20 );
        g.drawString( "Z=PAUSA"  , 5, 40 );

        // FRUIT
        g.setColor(Color.GREEN);
        g.fillOval(Math.round(xf), Math.round(yf), LADO, LADO);

        // SNAKE
        g.setColor(Color.RED);
        g.fillRect(Math.round(x), Math.round(y), LADO, LADO);

        // PAUSE
        if( pause )
        {
            g.setColor(Color.DARK_GRAY);
            g.fillRect(ANCHO/2-20, ALTO/2, 20, 50);
            g.fillRect(ANCHO/2+20, ALTO/2, 20, 50);
        }
    }

    private void dibuja() throws Exception {
        SwingUtilities.invokeAndWait(new Runnable() {
                public void run() {
                    paintImmediately(0, 0, ANCHO, ALTO);
                }
            });
    }

    public void fisica() throws Exception {
        long tiempoViejo = System.nanoTime();

        vx = 0; vy = 0;
        x = ANCHO/2-LADO/2; y = ALTO/2-LADO/2;
        xf = ajustar( (float) Math.random()*ANCHO, 0, ANCHO - LADO );
        yf = ajustar( (float) Math.random()*ALTO, 0, ALTO - LADO );

        while (true) {
            long tiempoNuevo = System.nanoTime();
            float dt = (tiempoNuevo - tiempoViejo) / 1000000000f;
            tiempoViejo = tiempoNuevo;

            if( teclaZ ) { vx=0; vy=0; pause=true; }
            //if( teclaX ) { score++; }
            //if( teclaC ) { score=0; }

            if( arriba && vy==0 ) { vy = -VELO; vx = 0; pause=false; }
            if( abajo && vy==0 ) { vy = VELO; vx = 0; pause=false; }
            if( izquierda && vx==0 ) { vx = -VELO; vy = 0; pause=false; }
            if( derecha && vx==0 ) { vx = VELO; vy = 0 ; pause=false; }

            x = ajustar(x + vx * dt, 0, ANCHO - LADO);
            y = ajustar(y + vy * dt, 0, ALTO - LADO);

            if( x==0 || x==ANCHO-LADO || y==0 || y==ALTO-LADO )
            {
                x = ANCHO/2-LADO/2; vx = 0;
                y = ALTO/2-LADO/2; vy = 0;

                score=0;

                xf = ajustar( (float) Math.random()*ANCHO, 0, ANCHO - LADO );
                yf = ajustar( (float) Math.random()*ALTO, 0, ALTO - LADO );
            }
            else if( colision(x,y,xf,yf)==true )
            {
                score++;

                xf = ajustar( (float) Math.random()*ANCHO, 0, ANCHO - LADO );
                yf = ajustar( (float) Math.random()*ALTO, 0, ALTO - LADO );
            }

            dibuja();
        }
    }

    public static void main(String[] args) throws Exception
    {
        JFrame jf = new JFrame("Snake");
        jf.addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e){ System.exit(0); } });
        jf.setResizable(false);
        Snake snake = new Snake();
        jf.getContentPane().add(snake);
        jf.pack();
        jf.setVisible(true);
        snake.fisica();
    }
}