I'm tryna create 4 image buttons and have the image changed to a check box whenever one of them is clicked. If a different image is clicked, every other button should revert to the original image and only the one that was last clicked should have the image with a check mark on it. It's kinda like radio buttons such that only one can be selected at  a time. How can i implement that?

class Check {
int x, y; // The x- and y-coordinates
int size; // Dimension (width and height)
color baseGray; // Default gray value
boolean checked = false; // True when the check box is selected
Check(int xp, int yp, int s, color b) {
x = xp;
y = yp;
size = s;
baseGray = b;
}
// Updates the boolean variable checked
void press(float mx, float my) {
if ((mx >= x) && (mx <= x+size) && (my >= y) && (my <= y+size)) {
checked = true; // Toggle the check box on and off
}
else
checked=false;
}
// Draws the box and an X inside if the checked variable is true
void display() {
stroke(255);
fill(baseGray);
rect(x, y, size, size);
if (checked == true) {
line(x, y, x+size, y+size);
line(x+size, y, x, y+size);
}
}
}

int numChecks = 4;
Check[] checks = new Check[numChecks];
void setup() {
size(100, 100);
int x = 14;
int y = 14;
for (int i = 0; i < numChecks; i++) {
checks[i] = new Check(x, y, 12, color(0));
x += 15;
if (x > 80) {
x = 14;
y += 15;
}
}
}


void draw() {
background(0);
for (int i=0; i<numChecks; i++) {
checks[i].display();
}
}
void mousePressed() {
for (int i = 0; i < numChecks; i++) {
checks[i].press(mouseX, mouseY);
}
}


from:
Processing:
a programming
handbook for
visual designers
and artists
Casey Reas
Ben Fry