1. import javax.swing.JOptionPane;
2. String str = "";
3. String newStr = "";
4. int cell1, cell2;
5. int celli, cellj;
6. boolean drag=false;
7. final int CELL_SIZE = 50;
8. final int NUM_ROW = 10;
9. final int NUM_COL = 10;
10. char[][] letters = new char[NUM_ROW][NUM_COL];
11. int code;
12. PFont letterFont;
13. void setup()
14. {
15.   initLetters(letters);
16.   // displayLetters(letters);
17.   size(NUM_ROW * CELL_SIZE, NUM_COL * CELL_SIZE);
18.   letterFont = createFont("Palatino", CELL_SIZE * 0.6);
19.   textFont(letterFont);
20.   textAlign(CENTER, CENTER);
21. }
22. void draw () {
23.   background(255);
24.   drawGrid();
25. }
26. // *************************************************************
27. void initLetters(char[][] a)
28. {
29.   int k = 0;
30.   String alphabet = " ABCDEFGHIJKLMNOPQRSTUVWXYZ";
31.   for (int i = 0; i < a.length; i++)
32.   {
33.     for (int j = 0; j < a[0].length; j++)
34.     {
35.       if (k<alphabet.length()) {
36.         a[i][j] = alphabet.charAt(k);
37.         k++;
38.       }
39.     }
40.   }
41. }
42. /*
43. void displayLetters(char[][] a)
44.  {
45.  for (int i = 0; i < a.length; i++)
46.  {
47.  for (int j = 0; j < a[0].length; j++)
48.  {
49.  print(a[i][j]);
50.  }
51.  }
52.  }
53.  */
54. void drawCell(int row, int col, char letter)
55. {
56.   stroke(0);
57.   noFill();
58.   rect(col * CELL_SIZE, row * CELL_SIZE, CELL_SIZE, CELL_SIZE);
59.   fill(0);
60.   text(letter, col * CELL_SIZE + CELL_SIZE/2, row * CELL_SIZE + CELL_SIZE/2);
61. }
62. void drawGrid()
63. {
64.   for (int i = 0; i < letters.length; i++)
65.   {
66.     for (int j = 0; j < letters[0].length; j++)
67.     {
68.       drawCell(i, j, letters[i][j]);
69.     }
70.   }
71. }
72. // *************************************************************
73. void mousePressed()
74. {
75.   if (mouseButton == LEFT) {
76.     for (int i = 0; i < NUM_COL; i++) {
77.       for (int j = 0; j < NUM_ROW; j++) {
78.         if (mouseY>i * CELL_SIZE && mouseY<i * CELL_SIZE+CELL_SIZE && mouseX>j * CELL_SIZE && mouseX<j * CELL_SIZE+CELL_SIZE) {
79.           str=""+letters[i][j];
80.           celli=i;
81.           cellj=j;
82.           drag=true; // start dragging
83.           break;
84.         }
85.       }
86.     }
87.   } // if
88. } // func
89. void mouseReleased()
90. {
91.   if (drag) {
92.     drag=false; // end dragging
93.     for (int i = 0; i < NUM_COL; i++) {
94.       for (int j = 0; j < NUM_ROW; j++) {
95.         if (mouseY>i * CELL_SIZE && mouseY<i * CELL_SIZE+CELL_SIZE && mouseX>j * CELL_SIZE && mouseX<j * CELL_SIZE+CELL_SIZE) {
96.           if (i!=celli || j!=cellj) {
97.             letters[i][j]=str.charAt(0);
98.             str="";
99.             break;
100.           }
101.         }
102.       }
103.     }
104.   }
105. }
106. void mouseClicked()
107. {
108.   if (mouseButton==RIGHT) {
109.     cell1=mouseY;
110.     cell2=mouseX;
111.     noLoop();
112.     newStr = (String)JOptionPane.showInputDialog("Enter a Character");
113.     loop();
114.     // go uppercase
115.     if (newStr != null)
116.     {
117.       str = newStr.toUpperCase();     
118.       fill(color(0));
119.       letters[cell1/CELL_SIZE][cell2/CELL_SIZE] = str.charAt(0);
120.       str=null;
121.     }
122.     drag=false;
123.   }
124. }
125. // *************************************************************

if (str.matches("\\d*")) {
  ...
}


What if you want only A - Z ??....I was trying to replace the ' d ' with 
other letters to see if I got lucky but no luck...any help??

Thank you!

str>='A' and str<='Z'

and use strToUpperCase()

of course

1. // lib
2. import javax.swing.JOptionPane;
3. // vars for dragging and input
4. String str = "";
5. int cell1, cell2;
6. int celli, cellj;
7. int seli, selj;
8. boolean drag = false;
9. // Font
10. PFont letterFont;
11. // The grid and related
12. final int CELL_SIZE = 50;
13. final int NUM_ROW = 10;
14. final int NUM_COL = 10;
15. char[][] letters = new char[NUM_ROW][NUM_COL];
16. // *************************************************************
17. void setup()
18. {
19.   size(NUM_ROW * CELL_SIZE, NUM_COL * CELL_SIZE);
20.   initLetters(letters);
21.   letterFont = createFont("Palatino", CELL_SIZE * 0.6);
22.   textFont(letterFont);
23.   textAlign(CENTER, CENTER);
24. }
25. void draw ()
26. {
27.   background(255);
28.   drawGrid();
29. }
30. // *************************************************************
31. void initLetters(char[][] a)
32. {
33.   // init
34.   int k = 0;
35.   String alphabet = " ABCDEFGHIJKLMNOPQRSTUVWXYZ";
36.   for (int i = 0; i < a.length; i++)
37.   {
38.     for (int j = 0; j < a[0].length; j++)
39.     {
40.       if (k<alphabet.length()) {
41.         a[i][j] = alphabet.charAt(k);
42.         k++;
43.       }
44.     }
45.   }
46. }
47. void drawCell(int row, int col, char letter)
48. {
49.   stroke(0);
50.   noFill();
51.   rect(col * CELL_SIZE, row * CELL_SIZE, CELL_SIZE, CELL_SIZE);
52.   fill(0);
53.   text(letter, col * CELL_SIZE + CELL_SIZE/2, row * CELL_SIZE + CELL_SIZE/2);
54. }
55. void drawGrid()
56. {
57.   for (int i = 0; i < letters.length; i++)
58.   {
59.     for (int j = 0; j < letters[0].length; j++)
60.     {
61.       drawCell(i, j, letters[i][j]);
62.     }
63.   }
64. }
65. // *************************************************************
66. void mousePressed()
67. {
68.   if (mouseButton == LEFT) {
69.     for (int i = 0; i < NUM_COL; i++) {
70.       for (int j = 0; j < NUM_ROW; j++) {
71.         if (mouseY>i * CELL_SIZE && mouseY<i * CELL_SIZE+CELL_SIZE && mouseX>j * CELL_SIZE && mouseX<j * CELL_SIZE+CELL_SIZE) {
72.           str=""+letters[i][j];
73.           celli=i;
74.           cellj=j;
75.           drag=true; // start dragging
76.           break;
77.         }
78.       }
79.     }
80.   } // if
81. } // func
82. void mouseReleased()
83. {
84.   if (mouseButton == LEFT) {
85.     if (drag) {
86.       drag=false; // end dragging
87.       for (int i = 0; i < NUM_COL; i++) {
88.         for (int j = 0; j < NUM_ROW; j++) {
89.           if (mouseY>i * CELL_SIZE && mouseY<i * CELL_SIZE+CELL_SIZE && mouseX>j * CELL_SIZE && mouseX<j * CELL_SIZE+CELL_SIZE) {
90.             if (i!=celli || j!=cellj) {
91.               letters[i][j]=str.charAt(0);
92.               str="";
93.               break;
94.             }
95.           }
96.         }
97.       }
98.     }
99.   }
100. }
101. void mouseClicked()
102. { 
103.   // for input
104.   String newStr = "";
105.   if (mouseButton==RIGHT) {
106.     cell1=mouseY;
107.     cell2=mouseX;
108.     noLoop();
109.     newStr = (String)JOptionPane.showInputDialog("Enter a Character");
110.     loop();
111.     // go uppercase
112.     if (newStr != null)
113.     {
114.       str = newStr.toUpperCase();     
115.       fill(color(0));
116.       letters[cell1/CELL_SIZE][cell2/CELL_SIZE] = str.charAt(0);
117.       str=null;
118.     }
119.     drag=false;
120.   }
121.   else
122.   {
123.     for (int i = 0; i < NUM_COL; i++) {
124.       for (int j = 0; j < NUM_ROW; j++) {
125.         if (mouseY>i * CELL_SIZE && mouseY<i * CELL_SIZE+CELL_SIZE && mouseX>j * CELL_SIZE && mouseX<j * CELL_SIZE+CELL_SIZE) {   
126.           seli=i;
127.           selj=j;
128.         }
129.       }
130.     }
131.   }
132. }
133. // *************************************************************
134. void keyPressed() {
135.   String input;
136.   if (key != CODED) {
137.     if (seli>-1&&selj>-1) {
138.       input=""+key;
139.       input=input.toUpperCase();
140.       letters[seli][selj] = input.charAt(0);
141.       selj++;
142.       if (selj>=NUM_COL) {
143.         selj=0;
144.         seli++;
145.       }
146.       if (seli>=NUM_ROW) {
147.         selj=0;
148.         seli=0;
149.       }
150.     }
151.   }
152. }
153. // **********************************************************

and use strToUpperCase()

of course

1. // lib
2. import javax.swing.JOptionPane;
3. // vars for dragging and input
4. String str = "";
5. int cell1, cell2;
6. int celli, cellj;
7. int seli, selj;
8. boolean drag = false;
9. // Font
10. PFont letterFont;
11. // The grid and related
12. final int CELL_SIZE = 50;
13. final int NUM_ROW = 11;
14. final int NUM_COL = 11;
15. char[][] letters = new char[NUM_ROW][NUM_COL];
16. // *************************************************************
17. void setup()
18. {
19.   size(NUM_ROW * CELL_SIZE, NUM_COL * CELL_SIZE);
20.   initLetters(letters);
21.   letterFont = createFont("Palatino", CELL_SIZE * 0.6);
22.   textFont(letterFont);
23.   textAlign(CENTER, CENTER);
24. }
25. void draw ()
26. {
27.   background(255);
28.   drawGrid();
29. }
30. // *************************************************************
31. void initLetters(char[][] a)
32. {
33.   // init
34.   int k = 0;
35.   String alphabet = "HOW ARE YOU";
36.   for (int i = 0; i < a.length; i++)
37.   {
38.     for (int j = 0; j < a[0].length; j++)
39.     {
40.       if (k<alphabet.length()) {
41.         a[j][i] = alphabet.charAt(k);
42.         k++;
43.       }
44.       else
45.         a[j][i] = ' ';
46.     }
47.   }
48. }
49. void drawCell(int row, int col, char letter)
50. {
51.   stroke(0);
52.   noFill();
53.   rect(col * CELL_SIZE, row * CELL_SIZE, CELL_SIZE, CELL_SIZE);
54.   fill(0);
55.   text(letter, col * CELL_SIZE + CELL_SIZE/2, row * CELL_SIZE + CELL_SIZE/2);
56. }
57. void drawGrid()
58. {
59.   for (int i = 0; i < letters.length; i++)
60.   {
61.     for (int j = 0; j < letters[0].length; j++)
62.     {
63.       drawCell(i, j, letters[i][j]);
64.     }
65.   }
66. }
67. // *************************************************************
68. void mousePressed()
69. {
70.   if (mouseButton == LEFT) {
71.     for (int i = 0; i < NUM_COL; i++) {
72.       for (int j = 0; j < NUM_ROW; j++) {
73.         if (mouseY>i * CELL_SIZE && mouseY<i * CELL_SIZE+CELL_SIZE && mouseX>j * CELL_SIZE && mouseX<j * CELL_SIZE+CELL_SIZE) {
74.           str=""+letters[i][j];
75.           celli=i;
76.           cellj=j;
77.           drag=true; // start dragging
78.           break;
79.         }
80.       }
81.     }
82.   } // if
83. } // func
84. void mouseReleased()
85. {
86.   if (mouseButton == LEFT) {
87.     if (drag) {
88.       drag=false; // end dragging
89.       for (int i = 0; i < NUM_COL; i++) {
90.         for (int j = 0; j < NUM_ROW; j++) {
91.           if (mouseY>i * CELL_SIZE && mouseY<i * CELL_SIZE+CELL_SIZE && mouseX>j * CELL_SIZE && mouseX<j * CELL_SIZE+CELL_SIZE) {
92.             if (i!=celli || j!=cellj) {
93.               letters[i][j]=str.charAt(0);
94.               str="";
95.               break;
96.             }
97.           }
98.         }
99.       }
100.     }
101.   }
102. }
103. void mouseClicked()
104. {
105.   // for input
106.   String newStr = "";
107.   if (mouseButton==RIGHT) {
108.     cell1=mouseY;
109.     cell2=mouseX;
110.     noLoop();
111.     newStr = (String)JOptionPane.showInputDialog("Enter a Character");
112.     loop();
113.     // go uppercase
114.     if (newStr != null)
115.     {
116.       str = newStr.toUpperCase();    
117.       fill(color(0));
118.       letters[cell1/CELL_SIZE][cell2/CELL_SIZE] = str.charAt(0);
119.       str=null;
120.     }
121.     drag=false;
122.   }
123.   else
124.   {
125.     for (int i = 0; i < NUM_COL; i++) {
126.       for (int j = 0; j < NUM_ROW; j++) {
127.         if (mouseY>i * CELL_SIZE && mouseY<i * CELL_SIZE+CELL_SIZE && mouseX>j * CELL_SIZE && mouseX<j * CELL_SIZE+CELL_SIZE) {  
128.           seli=i;
129.           selj=j;
130.         }
131.       }
132.     }
133.   }
134. }
135. // *************************************************************
136. void keyPressed() {
137.   String input;
138.   if (key != CODED) {
139.     if (seli>-1&&selj>-1) {
140.       input=""+key;
141.       input=input.toUpperCase();
142.       letters[seli][selj] = input.charAt(0);
143.       selj++;
144.       if (selj>=NUM_COL) {
145.         selj=0;
146.         seli++;
147.       }
148.       if (seli>=NUM_ROW) {
149.         selj=0;
150.         seli=0;
151.       }
152.     }
153.   }
154. }
155. // **********************************************************