Why PlainDocument() setted in JtextField.setDocument() excludes one character of the text

Question

Someone knows why in a JtextField, when I set the setDocument() property -class PlainDocument- when I execute the program, it shows me the field ok, but only I can enter N-1 characters, when I set the maxlength prop to N characters length.

// Block 1
txtPais.setDocument(new MaxLengthTextCntry());

I have another class which internally set the maximum length

// Block 2    
public class MaxLengthTextCntry extends MaxLengthGeneric{  
    public MaxLengthTextCntry(  
        {  
            super(2);  
        }  
    }

Finally the MaxLengthGeneric class

// Block 3
public abstract class MaxLengthGeneric extends PlainDocument {

        private int maxChars;

        public MaxLengthGeneric(int limit) {
            super();
            this.maxChars = limit;
        }

        public void insertString(int offs, String str, AttributeSet a)
                throws BadLocationException {
            if (str != null && (getLength() + str.length() < maxChars)) {
                super.insertString(offs, str, a);
            }
        }
    }

SOLUTION

Maintaining Block 2, I replaced block 1 with

((AbstractDocument) txtRucnumero.getDocument()).setDocumentFilter(new MaxLengthTextRuc());

Block 3 changed dependence from DocumentFilter. Don't forget to implement both parent methods insertString() and replace()!!

public abstract class MaxLengthGeneric extends DocumentFilter {

...

    @Override
    public void insertString(FilterBypass fb, int offs, String str,
            AttributeSet a) throws BadLocationException {

        if ((fb.getDocument().getLength() + str.length()) <= maxChars)
            super.insertString(fb, offs, str, a);
        else
            Toolkit.getDefaultToolkit().beep();
    }

    @Override
    public void replace(FilterBypass fb, int offs, int length, String str,
            AttributeSet a) throws BadLocationException {
        if ((fb.getDocument().getLength() + str.length() - length) <= maxChars)
            super.replace(fb, offs, length, str, a);
        else
            Toolkit.getDefaultToolkit().beep();
    }
}

Based on http://docs.oracle.com/javase/tutorial/uiswing/examples/components/TextComponentDemoProject/src/components/DocumentSizeFilter.java

OR SOLUTION 2 (Or maybe The importance of debugging for Jnewbies life: < replace with <=)

**    if (str != null && (getLength() + str.length() <= maxChars)) {**

Answer 1

MaxLengthTextArea is a class extended from PlainDocument: used just to set via parameter the number of characters I want for that field

As I suggested in my comment you should be using a DocumentFilter. Read the section from the Swing tutorial on Implementing a Document Filter for more information and a working example.