How set maximum of characters for the columns

Question

Hello I use a JTable and I want to set maximum of characters for the columns.
For example column 1 max 10 characters, column 2 max 20 characters, etc..
How can I do this?

Answer 1

The principle is as follows: a table uses certain input components for editing a cell value, e.g. a JCheckBox for Boolean-type values or a JTextField for textual/numerical values. By default, a JTextField doesn't have any size limit, so you can enter as many chars as you want. In order to change this behaviour, you'll have to
1.) create a JTextField that does have a size limit and
2.) set a CellEditor on the JTable which uses this manipulated JTextField.
An easy way for 1.) is to create a custom Document (the internal data representation for text components, the M-part of the MVC -- see javax.swing.text.Document) that doesn't accept any text beyond a given limit, e.g.:
public class LimitedDocument extends PlainDocument {
  private int max = 0;
  public LimitedDocument(int max) {
    this.max = max;
  public void insertString(int offset, String str, AttributeSet a) throws BadLocationException {
    // too long for the limit; get current contents, insert, and cut off trailing chars
    if ((getLength() + str.length()) > max) {
      StringBuffer buf = new StringBuffer(getText(0,getLength()));
      buf.insert(offset,str);
      remove(0,len); // remove current text contents
      super.insert(0,buf.toString().substring(0,max),a); // insert whole text
    // no problem, will fit
    else {
      super.insertString(offset,str,a);
}Then, in order to set the cell editor -- for example for the first column --, you can do as follows:
myTable.getColumnModel().getColumn(0).setCellEditor(new DefaultCellEditor(new JTextField(new LimitedDocument(5),"",5)));This will create a new DefaultCellEditor (see javax.swing.table) and initialize it with a given text field which will be responsible for any edition in this column. As the text field itself is created using a limit of 5, it should accept no text insertion beyond 5 chars.