Example of Decorator Pattern - LineNumberReader

Create a LineNumberReader like this

public class LineNumberReader extends BufferedReader 
{
    int lineNo = 1;
    public LineNumberReader(Reader in)
    {
        super((BufferedReader)in);
    }
    public void close() throws IOException
    {
        in.close();
    }
    /*
     * Add more responsibility of adding a line Number in the beginning
     */
    @Override
    public String readLine() throws IOException
    {
        String line = super.readLine();
        if(line==null) return line;
        line = lineNo + ":" + line;
        lineNo++;
        return line;
    }

}

Use the code as follows

public static void main(String[] args) throws FileNotFoundException 
    {
        File file = new File("D:\\Yogesh.txt");
        BufferedReader bufr = new BufferedReader(new FileReader(file));
        BufferedReader lnr = new LineNumberReader(bufr);
        Scanner sc ;
        String line = "";
        try
        {
            line=lnr.readLine();
            while(line!=null)
            {
                System.out.println(line);
                line=lnr.readLine();
            }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }