private void minusActionPerformed(java.awt.event.ActionEvent evt) {//GEN-FIRST:event_minusActionPerformed
        firstNum = (Double.parseDouble(String.valueOf(display.getText())));
        display.setText("");
        minusClick = 1;
        decimalClick = 0;        // TODO add your handling code here:
    }//GEN-LAST:event_minusActionPerformed