How is the write method in OutputStream called in this example?

Question

I found an example online and code is shown below. The TextAreaOutputStream is instantiated in TestAreaOutputStreamText. I don't understand how the write method is called in this example. How does this example work?

public class TextAreaOutputStream extends OutputStream {

   private final JTextArea textArea;
   private final StringBuilder sb = new StringBuilder();
   private String title;

   public TextAreaOutputStream(final JTextArea textArea, String title) {
      this.textArea = textArea;
      this.title = title;

      //sb.append(title + "> ");
   }

   @Override
   public void flush() {
       //this.textArea.setText("");
   }

   @Override
   public void close() {
   }

   @Override

   public void write(int b) throws IOException {


     if (b == '\r')
        return;

     if (b == '\n') {
         final String text = sb.toString() + "\n";
         SwingUtilities.invokeLater(new Runnable() {
           public void run() {

               textArea.append(text);
            }
        });
       sb.setLength(0);
         //sb.append(title + "> ");
        return;
 }

  sb.append((char) b);

   }

}

public class TextAreaOutputStreamTest extends JPanel {

   private JTextArea textArea = new JTextArea(15, 30);
   private TextAreaOutputStream taOutputStream = new TextAreaOutputStream(
     textArea, "Test");

   public TextAreaOutputStreamTest() {
      setLayout(new BorderLayout());
      add(new JScrollPane(textArea, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, 
        JScrollPane.HORIZONTAL_SCROLLBAR_NEVER));
      System.setOut(new PrintStream(taOutputStream));
}

   private static void createAndShowGui() {
      JFrame frame = new JFrame("Test");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(new TextAreaOutputStreamTest());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
           public void run() {
           createAndShowGui();
         }
      });
   }
 }

Answer 1

If it is used at all (it isn't in your posted code), it is used afters calls to this line System.setOut(new PrintStream(taOutputStream)); , per the documentation that will change the "Standard Output", which means all later calls to the System.out.print method(s) will be sent to the taOutputStream instance of TextAreaOutputStream .