You have to catch this exception.

This is the code before I modified it to work in my program.
import javax.swing.JOptionPane;//For user input dialogs
String y = "0";
class Button {
int x, y; // The x- and y-coordinates
int size; // Dimension (width and height)
color baseGray; // Default gray value
color overGray; // Value when mouse is over the button
color pressGray; // Value when mouse is over and pressed
boolean over = false; // True when the mouse is over
boolean pressed = false; // True when the mouse is over and pressed
Button(int xp, int yp, int s, color b, color o, color p) {
x = xp;
y = yp;
size = s;
baseGray = b;
overGray = o;
pressGray = p;
}
// Updates the over field every frame
void update() {
if ((mouseX >= x) && (mouseX <= x+size) &&
(mouseY >= y) && (mouseY <= y+size)) {
over = true;
} else {
over = false;
}
}
boolean press() {
if (over == true) {
pressed = true;
return true;
} else {
return false;
}
}
void release() {
pressed = false; // Set to false when the mouse is released
}
void display() {
if (pressed == true) {
fill(pressGray);
} else if (over == true) {
fill(overGray);
} else {
fill(baseGray);
}
stroke(255);
rect(x, y, size, size);
}
}




//Part button
Button button1, button2, button3;
int mode = 0;
//End of part button
void setup() {
size(100, 100);
smooth();
color gray = color(204);
color white = color(255);
color black = color(0);
button1 = new Button(10, 80, 10, gray, white, black);
button2 = new Button(25, 80, 10, gray, white, black);
button3 = new Button(40, 80, 10, gray, white, black);
}
void draw() {
background(204);
int y1 = Integer.parseInt(y);
println (y1);
manageButtons();
noStroke();
fill(0);
if (mode == 1) {
y = JOptionPane.showInputDialog(null,
"Enter new setpoint (0 to 120):",
"Setpoint adjustment",
JOptionPane.PLAIN_MESSAGE);

mode = 0;
} else if (mode == 2) {
ellipse(50, 40, 60, 60);
} else if (mode == 3) {
ellipse(100, 40, 60, 60);
}
}
void manageButtons() {
button1.update();
button2.update();
button3.update();
button1.display();
button2.display();
button3.display();
}
void mousePressed() {
if (button1.press() == true) { mode = 1; }
if (button2.press() == true) { mode = 2; }
if (button3.press() == true) { mode = 3; }
}
void mouseReleased() {
button1.release();
button2.release();
button3.release();
}
It does the same so you can see the problem. If I enter nothing or anything other than a number It returns an error.
Thanks
Bertus