How to Auto Calculate input numeric values of Text Field in JAVA
I suggest use a DocumentFilter
this will allow us to kill 2 birds with 1 stone.
1) we need to filter what is inputted to JTextField
s to make sure our calculation wont go wrong
2) We need to update the total on the fly i.e as more digits are added/removed.
Here is an example I made which uses DocumentFilter
and as you will see the Total field will be updated each time a new digit is entered/added to the JTextField
(s) (also it wont allow alphabetic characters etc only digits):
import java.awt.GridLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;
import javax.swing.text.DocumentFilter.FilterBypass;
public class DocumentFilterOnTheFlyCalculation {
public DocumentFilterOnTheFlyCalculation() {
createAndShowGui();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
new DocumentFilterOnTheFlyCalculation();
}
});
}
private void createAndShowGui() {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new GridLayout(4, 2));
JLabel label1 = new JLabel("Add:");
final JTextField jtf1 = new JTextField();
JLabel label2 = new JLabel("Add:");
final JTextField jtf2 = new JTextField();
JLabel label3 = new JLabel("Subtract:");
final JTextField jtf3 = new JTextField();
JLabel totalLabel = new JLabel("Total:");
final JTextField totalField = new JTextField("0");
totalField.setEditable(false);
DocumentFilter df = new DocumentFilter() {
@Override
public void insertString(FilterBypass fb, int i, String string, AttributeSet as) throws BadLocationException {
if (isDigit(string)) {
super.insertString(fb, i, string, as);
calcAndSetTotal();
}
}
@Override
public void remove(FilterBypass fb, int i, int i1) throws BadLocationException {
super.remove(fb, i, i1);
calcAndSetTotal();
}
@Override
public void replace(FilterBypass fb, int i, int i1, String string, AttributeSet as) throws BadLocationException {
if (isDigit(string)) {
super.replace(fb, i, i1, string, as);
calcAndSetTotal();
}
}
private boolean isDigit(String string) {
for (int n = 0; n < string.length(); n++) {
char c = string.charAt(n);//get a single character of the string
//System.out.println(c);
if (!Character.isDigit(c)) {//if its an alphabetic character or white space
return false;
}
}
return true;
}
void calcAndSetTotal() {
int sum = 0;
if (!jtf1.getText().isEmpty()) {
sum += Integer.parseInt(jtf1.getText());//we must add this
}
if (!jtf2.getText().isEmpty()) {
sum += Integer.parseInt(jtf2.getText());//we must add this
}
if (!jtf3.getText().isEmpty()) {
sum -= Integer.parseInt(jtf3.getText());//we must subtract this
}
totalField.setText(String.valueOf(sum));
}
};
((AbstractDocument) (jtf1.getDocument())).setDocumentFilter(df);
((AbstractDocument) (jtf2.getDocument())).setDocumentFilter(df);
((AbstractDocument) (jtf3.getDocument())).setDocumentFilter(df);
frame.add(label1);
frame.add(jtf1);
frame.add(label2);
frame.add(jtf2);
frame.add(label3);
frame.add(jtf3);
frame.add(totalLabel);
frame.add(totalField);
frame.pack();
frame.setVisible(true);
}
}
If you don't need an update for each keystroke, this alternate approach uses both a FocusListener
and a PropertyChangeListener
to update()
the total as changes accrue.