Java by API/org.eclipse.swt.events/VerifyEvent

VerifyEvent: doit

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.VerifyEvent;
import org.eclipse.swt.events.VerifyListener;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Text;
public class MainClass {
  public static void main(String[] a) {
    Display display = new Display();
    // Create the main window
    Shell shell = new Shell(display);
    Text fahrenheit = new Text(shell, SWT.BORDER);
    fahrenheit.setData("Type a temperature in Fahrenheit");
    fahrenheit.setBounds(20, 20, 100, 20);
    fahrenheit.addVerifyListener(new VerifyListener() {
      public void verifyText(VerifyEvent event) {
        // Assume we don"t allow it
        event.doit = false;
        // Get the character typed
        char myChar = event.character;
        String text = ((Text) event.widget).getText();
        // Allow "-" if first character
        if (myChar == "-" && text.length() == 0)
          event.doit = true;
        // Allow 0-9
        if (Character.isDigit(myChar))
          event.doit = true;
        // Allow backspace
        if (myChar == "\b")
          event.doit = true;
      }
    });
    shell.open();
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch()) {
        display.sleep();
      }
    }
    display.dispose();
  }
}