in my code

  if (isInTarget(curParticle.xPos, curParticle.yPos, txPos, tyPos, diam/2)) {

Cannot find anything named "curParticle"

even though I have specified curParticle a few times before in my code. 

Did I miss something important?><

I will paste my code below this time..

/------------------------------------

Like Chrisir said you must rethink the process.

You have to verify the goal in the update position method.

Look at the ArrayListClass example it is clear.

2. // - - - -
3. float gravity_x;
4. float gravity_y;
5. // - - - -
6. float tyPos;
7. float txPos;
8. float targetVelocity;
9. float diam;
10. // - - - -
11. float gunVelocity;
12. float gxPos;
13. float gyPos;
14. 
    
15. boolean shot;
16. 
    
17. ArrayList<Particle> particles = new ArrayList<Particle>();
18. 
    
19. void setup() {
20.   size(500, 500);
21. 
    
22.   targetVelocity= -3;
23.   gunVelocity = 2;
24.   gravity_x = 0.023;
25.   gravity_y = 3;
26.   tyPos = 400;
27.   txPos = 300;
28. 
    
29.   gxPos = 10;
30.   gyPos = 200;
31.   diam = 100;
32. }
33. 
    
34. class Particle {
35. 
    
36.   float xPos, yPos, xVel, yVel;
37. 
    
38.   Particle(float xPos, float yPos, float xVel, float yVel) {
39.     this.xPos = xPos; 
40.     this.yPos = yPos; 
41.     this.xVel = xVel; 
42.     this.yVel = yVel;
43.   }
44. 
    
45.   void shootBullet() {
46.     xPos += xVel;
47.     xPos += -gravity_x;
48.     yPos += gravity_y;
49.     //    if (abs(xPos - width/2 - 30) > width/2 - 16) {
50.     //      xPos = -30;
51.     //    }
52.     //    if (abs(yPos - height/2 - 30) > height/2 - 16) {
53.     //      yPos = -30;
54.   }
55. 
    
56.   void drawBullet() {
57.     pushMatrix();
58.     fill(0);
59.     translate(xPos, yPos);
60.     ellipse(0, 0, 32, 32);
61.     popMatrix();
62.   }
63. }
64. 
    
65. void draw() {
66.   background(255);
67. 
    
68.   drawTarget();
69.   drawGun();
70.   showBullets();
71. }
72. 
    
73. void showBullets() {
74.   for (int i = 0; i < particles.size(); i++) {
75.     Particle curParticle = particles.get(i);
76.     curParticle.shootBullet();
77.     curParticle.drawBullet();
78.     if (isInTarget(curParticle.xPos, curParticle.yPos, txPos, tyPos, diam)) {
79.       println("Yeah !");
80.       particles.remove(i);
81.     }
82.   }
83. }
84. 
    
85. void drawGun() {
86.   fill(0);
87.   rect(gxPos, gyPos, 60, 20);
88.   rect(gxPos, gyPos, 20, 50);
89.   gyPos += gunVelocity;
90.   if (gyPos <= 0) {
91.     gunVelocity = -gunVelocity;
92.   } 
93.   if (gyPos + 50 >= 499) {
94.     gunVelocity = -gunVelocity;
95.   }
96. }
97. 
    
98. void drawTarget() {
99.   noStroke();
100.   fill(255, 0, 0);
101.   ellipse(txPos, tyPos, diam, diam);
102.   fill(255);
103.   ellipse(txPos, tyPos, 80, 80);
104.   fill(255, 0, 0);
105.   ellipse(txPos, tyPos, 60, 60);
106.   fill(255);
107.   ellipse(txPos, tyPos, 40, 40);
108.   tyPos += targetVelocity;
109.   if (tyPos - 50 <= 0) {
110.     targetVelocity = -targetVelocity;
111.   } 
112.   if (tyPos + 50 >= 499) {
113.     targetVelocity = -targetVelocity;
114.   }
115. }
116. 
     
117. void shouldShoot() {
118. }
119. 
     
120. void mouseClicked() {
121.   println("clicked");
122.   Particle newParticle = new Particle(gxPos, gyPos, 10, 5);
123.   particles.add(newParticle);
124. }
125. 
     
126. boolean isInTarget(float x, float y, float a, float b, float r) {
127.   if (dist(x, y, a, b) <=r) {
128.     return true;
129.   } 
130.   else {
131.     return false;
132.   }
133. }