Maximum length of JTextField and only accepts numbers?

问题

I want the user to input a maximum of 8 numbers as it is a field for Mobile number. This is my JTextField.

    txtMobile = new JTextField();
    txtMobile.setColumns(10);
    txtMobile.setBounds(235, 345, 145, 25);
    add(txtMobile);

While we're at it, how do I check for invalid characters like >> '^%$* in a JTextField?

1)Maximum Length

2)Accepts only numbers

3)Check for invalid characters

4)Check if it's a valid email address

Please help :D

回答1:

You could use a JFormattedField, check out How to Use Formatted Text Fields, but they tend not to restrict the user from entering what ever they want, but instead does a post validation of the value to see if meets the needs of the format you sepcify

You could use a DocumentFilter instead, which would allow you to filter the input in real time.

Take a look at Implementing a Document Filter and MDP's Weblog for examples

回答2:

Look at this sample example it will only accepts numbers as an input, as an answer to your second requirement.

public class InputInteger
{
private JTextField tField;
private JLabel label=new JLabel();
private MyDocumentFilter documentFilter;

private void displayGUI()
{
    JFrame frame = new JFrame("Input Integer Example");
    frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

    JPanel contentPane = new JPanel();
    contentPane.setBorder(
        BorderFactory.createEmptyBorder(5, 5, 5, 5));
    tField = new JTextField(10);
    ((AbstractDocument)tField.getDocument()).setDocumentFilter(
            new MyDocumentFilter());
    contentPane.add(tField); 
    contentPane.add(label);


    frame.setContentPane(contentPane);
    frame.pack();
    frame.setLocationByPlatform(true);
    frame.setVisible(true);
}
public static void main(String[] args)
{
    Runnable runnable = new Runnable()
    {
        @Override
        public void run()
        {
            new InputInteger().displayGUI();
        }
    };
    EventQueue.invokeLater(runnable);
}
}

class MyDocumentFilter extends DocumentFilter{
    private static final long serialVersionUID = 1L;
    @Override
public void insertString(FilterBypass fb, int off
                    , String str, AttributeSet attr) 
                            throws BadLocationException 
{
    // remove non-digits
    fb.insertString(off, str.replaceAll("\\D++", ""), attr);
} 
@Override
public void replace(FilterBypass fb, int off
        , int len, String str, AttributeSet attr) 
                        throws BadLocationException 
{
    // remove non-digits
    fb.replace(off, len, str.replaceAll("\\D++", ""), attr);
}
}

来源：https://stackoverflow.com/questions/21570245/maximum-length-of-jtextfield-and-only-accepts-numbers

标签

numbers

character

max

jtextfield