The problem is where you put the break;

Try running the following and you'll understand:

1. for (int i=0; i< 10; i++){
2.    println("item: " + i);
3.    break;
4. }

Maybe you only meant to break if the condition returns true ;)

edit: scratch that - blindfish is right, i didn't notice the break was placed outside the condition

i understand your example, but do i need to remove the break or move it somewhere else?

Well that obviously depends on what you want.

If you move it into the condition where mouseselected = true then the moment the mouse is over any of the fFighters you'll break out of the loop with only that fighter's property set to true.  Some would argue that this is more efficient (you avoid 'unnecessary' iterations of the loop), but it's not always desired...  For example if the objects overlap only the 'top' object will have the mouseselected property set to true since the loop will break out at this point.  If you want to be able to select multiple objects then you need to remove the break altogether...

1. boolean mouseselected;   

 

1. if(mouseselected) {
         stroke(0);     
         fill(sR,sG,sB);
         triangle(x,y,x+5,y+12.5,x-5,y+12.5);
       }
       else {
       }

1. public void mouseOver() {
       for(int i  = 0; i < ffighters.size(); i++) {
         fFighter ff = (fFighter)ffighters.get(i);
         if(mouseX > ff.x-5 && mouseX < ff.x+5 && mouseY > ff.y-5 && mouseY < ff.y+5) {
           ff.mouseselected = true;
           break;
         }
         else {
           ff.mouseselected = false;
         }
       }
     }

tried that and nothing happens

Posting random lines of code like that isn't going to help us to help you.  For example is: "boolean mouseselected;" declared globally or is it a property of your fFighter class?  If it's global then it's fairly obvious why the code isn't working; but otherwise there are all kinds of potential causes to your problems...

1. class fFighter {
     float x; //Current x posn
     float y; //Current y posn
     float destx; //Destination x posn
     float desty; //Destination y posn
     float speed; //Speed of movement
     float movingAngle; //Angle of movement
     boolean selected; //Selected?
     boolean moving; //Moving?
     boolean irangeon; //Intel Range
     boolean mrangeon; //Mil Range
     boolean mouseselected; //mouseover change
2. 
     public fFighter() {
       x = random(width);
       y = random(height);
       selected = moving = false;
     }
3.   public fFighter(float startx,float starty) {
       x = startx;
       y = starty;
       speed = 0.02; //Speed of movement
       selected = moving = false;
     }
4.   public void tick() { //Definition of 'moving'
       if(moving) {
         x += cos(movingAngle)*speed;
         y += sin(movingAngle)*speed;
         if(sqrt(sq(destx-x)+sq(desty-y)) <= speed) {
           moving = false;
         }
       }
5.     if(irangeon) {
         ellipseMode(CENTER);
         noFill();
         stroke(iR,iG,iB);
         ellipse(x,y+5,51,51);
       }
       else {
       }
6.     if(mrangeon) {
         noFill();//(sR,sG,sB);
         stroke(mR,mG,mB);
         ellipseMode(CENTER);
         ellipse(x,y+5,50,50);
       }
       else {
       }
7.     if(mouseselected) {
         stroke(0);     
         fill(sR,sG,sB);
         triangle(x,y,x+5,y+12.5,x-5,y+12.5);
       }
       else {
       }
8.     if(selected) { //If selected...
         stroke(0);     
         fill(sR,sG,sB);
         triangle(x,y,x+5,y+12.5,x-5,y+12.5);
         noFill();//(sR,sG,sB);
         stroke(mR,mG,mB);
         ellipseMode(CENTER);
         ellipse(x,y+5,50,50);
         stroke(iR,iG,iB);
         ellipse(x,y+5,51,51);
       }
       else { //If not selected...
         stroke(0);
         fill(fR,fG,fB);
       }
       triangle(x,y,x+5,y+12.5,x-5,y+12.5); //Shape of unit
     }
9.   public void mouseOver() {
       for(int i  = 0; i < ffighters.size(); i++) {
         fFighter ff = (fFighter)ffighters.get(i);
         if(mouseX > ff.x-5 && mouseX < ff.x+5 && mouseY > ff.y-5 && mouseY < ff.y+5) {
           ff.mouseselected = true;
           break;
         }
         else {
           ff.mouseselected = false;
         }
       }
     }
10.   public void goTo(float dx, float dy) { //Movement code
        destx = dx;
        desty = dy;
        movingAngle = atan2(dy-y,dx-x);
        moving = true;
      }
    }

Well this more or less works, though still needs a fair amount of work:

1. ArrayList fighters;
2. int iR = 255;
3. int iG = 0;
4. int iB = 0;
5. int mR = 0;
6. int mG = 255;
7. int mB = 0;
8. int sR = 0;
9. int sG = 0;
10. int sB = 255;
11. int fR = 255;
12. int fG = 255;
13. int fB = 0;
14. void setup() {
15.    size(600,400);
16.    fighters= new ArrayList();
17.    for (int i=0; i < 20; i++){
18.      fighters.add(new fFighter());
19.    }
20. }
21. void draw() {
22.   for (int i=0; i < fighters.size(); i++){
23.     fFighter fighter = (fFighter) fighters.get(i);
24.     fighter.tick();
25.   }
26.  
27.   mouseOver();
28.  
29.  
30. }
31. // This doesn't belong in the fFighter class!!!
32. void mouseOver() {
33.    for(int i  = 0; i < fighters.size(); i++) {
34.             fFighter ff = (fFighter)fighters.get(i);
35.             if(mouseX > ff.x-5 && mouseX < ff.x+5 && mouseY > ff.y-5 && mouseY < ff.y+5) {
36.               ff.mouseselected = true;
37.               println("over!");
38.             }
39.             else {
40.               ff.mouseselected = false;
41.             }
42.           }
43. }
44. class fFighter {
45.         float x; //Current x posn
46.         float y; //Current y posn
47.         float destx; //Destination x posn
48.         float desty; //Destination y posn
49.         float speed; //Speed of movement
50.         float movingAngle; //Angle of movement
51.         boolean selected; //Selected?
52.         boolean moving; //Moving?
53.         boolean irangeon; //Intel Range
54.         boolean mrangeon; //Mil Range
55.         boolean mouseselected; //mouseover change
56.         public fFighter() {
57.           x = random(width);
58.           y = random(height);
59.           selected = moving = false;
60.         }
61.        
62.     public fFighter(float startx,float starty) {
63.           x = startx;
64.           y = starty;
65.           speed = 0.02; //Speed of movement
66.           selected = moving = false;
67.         }
68.        
69.     public void tick() { //Definition of 'moving'
70.           if(moving) {
71.             x += cos(movingAngle)*speed;
72.             y += sin(movingAngle)*speed;
73.             if(sqrt(sq(destx-x)+sq(desty-y)) <= speed) {
74.               moving = false;
75.             }
76.           }
77.          
78.     if(irangeon) {
79.             ellipseMode(CENTER);
80.             noFill();
81.             stroke(iR,iG,iB);
82.             ellipse(x,y+5,51,51);
83.           }
84.           else {
85.           }
86.          
87.     if(mrangeon) {
88.             noFill();//(sR,sG,sB);
89.             stroke(mR,mG,mB);
90.             ellipseMode(CENTER);
91.             ellipse(x,y+5,50,50);
92.           }
93.           else {
94.           }
95.          
96.     if(mouseselected) {
97.             stroke(0);    
98.             fill(sR,sG,sB);
99.             triangle(x,y,x+5,y+12.5,x-5,y+12.5);
100.           }
101.           // ELSE!!!!
102.           else if(selected) { //If selected...
103.             stroke(0);    
104.             fill(sR,sG,sB);
105.             triangle(x,y,x+5,y+12.5,x-5,y+12.5);
106.             noFill();//(sR,sG,sB);
107.             stroke(mR,mG,mB);
108.             ellipseMode(CENTER);
109.             ellipse(x,y+5,50,50);
110.             stroke(iR,iG,iB);
111.             ellipse(x,y+5,51,51);
112.           }
113.           // In its original state this overrode all previous colour settings...
114.           else { //If not selected...
115.             stroke(0);
116.             fill(fR,fG,fB);
117.           }
118.           triangle(x,y,x+5,y+12.5,x-5,y+12.5); //Shape of unit
119.         }
120.        
121.    
122.     public void goTo(float dx, float dy) { //Movement code
123.           destx = dx;
124.           desty = dy;
125.           movingAngle = atan2(dy-y,dx-x);
126.           moving = true;
127.         }
128. }

First off not seeing how you go about calling that mouseOver code didn't help; but in its original state it didn't make a great deal of sense: you iterated over the whole collection of fighters; which an individual fighter doesn't really know about.  Better to have a mouseOver function that checks against itself then it's just a matter of calling it from within tick() which presumably you're calling on all fighters from a loop in draw...  I'll leave that to you.

Next up:

1.      if(irangeon) {
2.             //snip
3.           }
4.           else {
5.           }
6.          
7.     if(mrangeon) {
8.            //snip
9.           }
10.           else {
11.           }
12.          
13.     if(mouseselected) {
14.            //snip
15.           }
16.          else {
17.          }
18.          
19.           if(selected) { //If selected...
20.              // snip
21.           }
22.           // This overrides all previous settings except if selected == true
23.           else { //If not selected...
24.             stroke(0);
25.             fill(fR,fG,fB);
26.           }

Since all those conditions affect the fill colour you need to chain them together with else ifs in an order of priority.  Otherwise the last condition overrides all the others except when selected == true...

Even then, and as you'll see from my 'working' code above, your mouseOver test doesn't quite correspond with the position of the ships...