You should check your field before parse double:
private void jButton4ActionPerformed(java.awt.event.ActionEvent evt) { double AText = ParseDouble(angleAField.getText()); double BText = ParseDouble(angleBField.getText()); double CText = ParseDouble(angleCField.getText()); double aText = ParseDouble(sideaField.getText()); double bText = ParseDouble(sidebField.getText()); double cText = ParseDouble(sidecField.getText()); // other code here same } double ParseDouble(String strNumber) { if (strNumber != null && strNumber.length() > 0) { try { return Double.parseDouble(strNumber); } catch(Exception e) { return -1; // or some value to mark this field is wrong. or make a function validates field first ... } } else return 0; }