I've been progamming an sketch in which you press any key on the key board and it gives you the ascii and binary values. That part is working great. However, i want to be able to represent the binary value in a graphical way, so my sketch is progammed to draw grey circles for 0 and green circles for 1(the binary values). But when i run my sketch it highlights some part with the function charAt() on it and then gives this error messages: 

Exception in thread "Animation Thread" java.lang.StringIndexOutOfBoundsException: String index out of range: 1

at java.lang.String.charAt(String.java:558)

at char_to_bin_.draw(char_to_bin_.java:73)

at processing.core.PApplet.handleDraw(PApplet.java:1631)

at processing.core.PApplet.run(PApplet.java:1530)

at java.lang.Thread.run(Thread.java:655)

i hope that anypne can explain me how t slove this. Thank a lot.

CODE:

1. int letter = 0;  //declare variables
2. char car;
3. char compare;
4. String binaryString ;
5. 
   
6. 
   
7. void setup(){
8. size(1000,300);   //size and background color
9. background(0);
10. }
11. 
    
12. void draw(){
13.   background(0);
14.   fill(255);
15. binaryString=binary(letter);   //convert to bin
16.      
17.  if(binaryString.length()<8){                   //make sure the binary string always has 8 characters 
18.    if(binaryString.length()==7){               //to make sure we draw 8 circles
19.      binaryString = "0" + binaryString;
20.    }else{
21.      if(binaryString.length()==6){
22.        binaryString = "00" + binaryString;
23.        }else{
24.        if(binaryString.length()==5){
25.          binaryString = "000" + binaryString;
26.          }else{
27.        if(binaryString.length()==4){
28.          binaryString = "0000" + binaryString;
29.        }}}}}
30. 
    
31. 
    
32. 
    
33. 
    
34. if(letter <300){       //write on the screen our values
35. text(car,200,50);
36. text (letter,390,50);
37. text(binaryString,550,50 );
38. 
    
39. }
40. text("the binary is:",450,50);                  //write on the screen the desciption of our values
41. text("the ascii value is:",250,50);
42. text("the character received is:",10,50);
43. 
    
44. 
    
45.   for(int i=0; i<8 ; ++i){                    //draw the circles with grey for 0 and green for 1
46.     if(binaryString.charAt(i)==0){       //this is the problematic line
47.       fill(100);
48.     }else{
49.       fill(0,255,0);}      
50.       if(i==0){
51.        i=1;
52.        ellipse(i*100,height/2,80,80 );
53.        i=0;
54.      }else{
55. ellipse(i*100,height/2,80,80 );}
56. }
57. 
    
58. 
    
59. }
60.  void keyPressed(){   //the part to analyse the key that was pressed
61.    letter=key;
62.    car=key;
63.  }