import javax.swing.text.AttributeSet;   
import javax.swing.text.BadLocationException;   
import javax.swing.text.PlainDocument; 

public class NumOnly extends PlainDocument{        
    public void insertString(int offs,String str,AttributeSet a) throws BadLocationException{   
        for(int i=0;i<str.length();i++){  
            if(str.charAt(i)<'0'||str.charAt(i)>'9'){   
                return;   
            } 
        }   
        super.insertString(offs,str,a);  
            
    }
}