1. int frogx = 50;
2. int frogy = 50;
3. PImage frogimg;
4. void setup() {
5.    size(300,200);
   
6.    frogimg = loadImage("frog.gif");
7. }
8. void draw() {
9.    background (255);
   
10.    image(frogimg, frogx, frogy);
11. }
12. void keyPressed() {
13.    if (keyCode == 39) {
14.         frogx = frogx + 20;  //right arrow
15.    }
16.   if (keyCode == 37) {
17.         frogx = frogx - 20; //left arrow
18.   }
19.    if (keyCode == 38) {
20.       frogy = frogy - 20;  //up arrow
21.    }
22.    if (keyCode == 40) {
23.       frogy = frogy + 20;  //down arrow
24.    }
25. }

class Car
{
    color col;
    int x, y, w, h;
    int speed;

    /**
     *  Constructor for cars.
     *
     *  @param c The color of the car.
     *  @param x The x location of the center of the car.
     *  @param y The y location of the center of the car.
     *  @param w The width of the car.
     *  @param h The height of the car.
     *  @param s The speed of the car in pixels moved per frame.
     */
    Car(color c, int x, int y, int w, int h, int s)
    {
        this.col = c;
        this.x = x;
        this.y = y;
        this.w = w;
        this.h = h;
        this.speed = s;
    }

    //  Draw the car on the sketch.
    void draw()
    {
        noStroke();
        fill(this.col);
        rect(this.x, this.y, this.w, this.h);
    }

    //  Move the car.
    //  Car location wraps when it reaches the right edge.
    void move()
    {
        this.x += this.speed;
        if (this.x > width) {
            this.x = 0;
        }
    }
}

1. //  Define sketch size parameters.
2. final int WIDTH = 200;
3. final int HEIGHT = WIDTH;
4. final int MIDDLE = WIDTH / 2;
5. //  Define symbolic color constants.
6. final color BLACK = color(0);
7. final color RED = color(255, 0, 0);
8. final color GREEN = color(0, 255, 0);
9. final color BLUE = color(0, 0, 255);
10. final color YELLOW = color(255,247,3);
11. //  Define car dimensions.
12. final int CAR_WIDTH = 30;
13. final int CAR_HEIGHT = 10;
14. int frogx = 165;
15. int frogy = 170;
16. PImage frogimg;
17. //  Declare the cars.
18. Car car1;
19. Car car2;
20. Car car3;
21. //  Setup the initial conditions.
22. //  Create the cars.
23. void setup()
24. {
25.   size(WIDTH, HEIGHT);
26.   rectMode(CENTER);
27.   car1 = new Car(RED, 0, 100, CAR_WIDTH, CAR_HEIGHT, 2);
28.   car2 = new Car(GREEN, 50, 50, CAR_WIDTH, CAR_HEIGHT, 1);
29.   car3 = new Car(BLUE, 150, 150, CAR_WIDTH, CAR_HEIGHT, 2);
30.   frogimg = loadImage("frog.gif");
31. }
32. //  Draw the road, and the cars.
33. void draw()
34. {
35.   background(BLACK);
36.   strokeWeight(4);
37.   stroke(255,247,3);
38.   line(200,20,0,20);
39.   line(200,180,0,180);
40.   //////////////////////
41.   //fill(0);
42.   for(int i = 14; i<width; i+=14) {
43.     noStroke();
44.     fill(190);
45.     rect (i,height/2.6,7,4);
46.   }
47.   ///////////////////////
48.   for(int i = 14; i<width; i+=14) {
49.     noStroke();
50.     fill(190);
51.     rect (i,height/1.6,7,4);
52.   }
53.   //////////////////////
54.   car1.draw();
55.   car1.move();
56.   car2.draw();
57.   car2.move();
58.   car3.draw();
59.   car3.move();
60.   /////////////////////////
61. //  image(frogimg, 165, 170);
62.   //////////////////////////////
63.   /// PImage b;
64.   //b = loadImage("frog.gif");
65.   image(frogimg, frogx, frogy, 25,25);
66. }
67. void keyPressed() {
68.   if (keyCode == 39) {
69.     frogx = frogx + 20;  //right arrow
70.   }
71.   if (keyCode == 37) {
72.     frogx = frogx - 20; //left arrow
73.   }
74.   if (keyCode == 38) {
75.     frogy = frogy - 20;  //up arrow
76.   }
77.   if (keyCode == 40) {
78.     frogy = frogy + 20;  //down arrow
79.   }
80. }
81. class Car
82. {
83.   color col;
84.   int x, y, w, h;
85.   int speed;
86.   /**
87.    *  Constructor for cars.
88.    *
89.    *  @param c The color of the car.
90.    *  @param x The x location of the center of the car.
91.    *  @param y The y location of the center of the car.
92.    *  @param w The width of the car.
93.    *  @param h The height of the car.
94.    *  @param s The speed of the car in pixels moved per frame.
95.    */
96.   Car(color c, int x, int y, int w, int h, int s)
97.   {
98.     this.col = c;
99.     this.x = x;
100.     this.y = y;
101.     this.w = w;
102.     this.h = h;
103.     this.speed = s;
104.   }
105.   //  Draw the car on the sketch.
106.   void draw()
107.   {
108.     noStroke();
109.     fill(this.col);
110.     rect(this.x, this.y, this.w, this.h);
111.   }
112.   //  Move the car.
113.   //  Car location wraps when it reaches the right edge.
114.   void move()
115.   {
116.     this.x += this.speed;
117.     if (this.x > width) {
118.       this.x = 0;
119.     }
120.   }
121. }

getting a nullpointerexception at   image(frogimg, frogx, frogy, 25,25);