From Console ouput to TextArea in GUI Java

Question

I'm a real beginner in Java and am trying to redirect the console output to a TextArea of a GUI I made in Java (Netbeans).

This is part of a bigger project but I first created a small program which outputs data to the console and a GUI which only reads this one line. Could somebody help me to get this done? I've tried already several solutions containing append, JFrame etc. still without success.

Thank you in advance!

The program to display text on the console is:

public class ConsoleToGUI {

    public void run(){
        for (int i = 0; i < 5; i++){
            System.out.println("Test program");
        }
    }

    public static void main(String[] args){
        ConsoleToGUI ctg = new ConsoleToGUI();
        ctg.run();
    }

The GUI I've created with a TextArea :

Update Underneath I've posted the three classes (including the GUI code) which I've adjusted thanks to dosenfant's solution, thank you! However, I might still be doing something wrong since it is not working as of yet. Please your advise!

import java.io.PrintStream;
import javax.swing.*;

public class ConsoleToGUI {

public ConsoleToGUI() {
    DisplayUI gui = new DisplayUI();
    System.setOut(new PrintStream(new RedirectingOutputStream(gui), true));
    gui.start();
}


public void run(){

    for (int i = 0; i < 5; i++){
    JTextArea jTextArea1 = new JTextArea();
    System.out.println("Test program");
    }
}

public static void main(String[] args){
    ConsoleToGUI ctg = new ConsoleToGUI();
    ctg.run();
 }
}  

GUI Class

public class DisplayUI extends javax.swing.JFrame {

/**
 * Creates new form DislapUI
 */
public DisplayUI() {
    initComponents();
}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    jPanel1 = new javax.swing.JPanel();
    jScrollPane1 = new javax.swing.JScrollPane();
    jTextArea1 = new javax.swing.JTextArea();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    jPanel1.setBorder(javax.swing.BorderFactory.createTitledBorder(null, 
    "Console Output: ", 
    javax.swing.border.TitledBorder.DEFAULT_JUSTIFICATION, 
    javax.swing.border.TitledBorder.DEFAULT_POSITION, new 
    java.awt.Font("Tahoma", 1, 11), new java.awt.Color(51, 153, 255))); // 
    NOI18N

    jTextArea1.setEditable(false);
    jTextArea1.setColumns(20);
    jTextArea1.setRows(5);
    jScrollPane1.setViewportView(jTextArea1);

    javax.swing.GroupLayout jPanel1Layout = new 
    javax.swing.GroupLayout(jPanel1);
    jPanel1.setLayout(jPanel1Layout);
    jPanel1Layout.setHorizontalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(jPanel1Layout.createSequentialGroup()
            .addContainerGap()
            .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 348, Short.MAX_VALUE)
            .addContainerGap())
    );
    jPanel1Layout.setVerticalGroup(
        jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(jPanel1Layout.createSequentialGroup()
            .addContainerGap()
            .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 70, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addContainerGap(15, Short.MAX_VALUE))
    );

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
            .addContainerGap())
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
    );

    pack();
}// </editor-fold>                        

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {
    /* Set the Nimbus look and feel */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */
    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(DisplayUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(DisplayUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(DisplayUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(DisplayUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>
    //</editor-fold>

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new DisplayUI().setVisible(true);
        }
    });
}

public void start() {
    jPanel1.setVisible(true);
}

public void appendText(String text) {
    jTextArea1.append(text);
}

// Variables declaration - do not modify                     
private javax.swing.JPanel jPanel1;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JTextArea jTextArea1;
// End of variables declaration                   

}

RedirectingOutputStream
import java.io.IOException; import java.io.OutputStream;

public class RedirectingOutputStream extends OutputStream {

    private DisplayUI gui;

    public RedirectingOutputStream(DisplayUI gui) {
        this.gui = gui;
    }

    @Override
    public void write(int b) throws IOException {
        gui.appendText(String.valueOf((char) b));
    }
 }

Answer 1

If your goal is to catch all output to System.out (what your code snippet suggests to me) you might want to do the following:

1. Create a subclass of PrintStream which in its write methods also (or exclusively) redirects to the text area.
2. Set the new PrintStream as System.out

See this example for JavaFX which does the same (except that they are not forwarding to a Swing component, but conceptually it's the same).

---

Example:

package example;

import java.io.PrintStream;

public class ConsoleToGUI {

    public ConsoleToGUI() {
        GUI gui = new GUI();
        System.setOut(new PrintStream(new RedirectingOutputStream(gui), true));
        gui.start();
    }

    public void run() {
        for (int i = 0; i < 5; i++) {
            System.out.println("Test program");
        }
    }

    public static void main(String[] args) {
        ConsoleToGUI ctg = new ConsoleToGUI();
        ctg.run();
    }
}

---

package example;

import java.awt.BorderLayout;

import javax.swing.JFrame;
import javax.swing.JTextArea;

public class GUI {

    private JTextArea textArea;
    private JFrame frame;

    public GUI() {
        frame = new JFrame("Example");
        frame.setBounds(0, 0, 600, 400);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        textArea = new JTextArea();
        frame.getContentPane().add(textArea, BorderLayout.CENTER);
    }

    public void start() {
        frame.setVisible(true);
    }

    public void appendText(String text) {
        textArea.append(text);
    }
}

---

package example;

import java.io.IOException;
import java.io.OutputStream;

public class RedirectingOutputStream extends OutputStream {

    private GUI gui;

    public RedirectingOutputStream(GUI gui) {
        this.gui = gui;
    }

    @Override
    public void write(int b) throws IOException {
        gui.appendText(String.valueOf((char) b));
    }
}

Answer 2

If you want to write in the JTextArea after clearing it, you can use the following:

jTextArea.setText("Test program");

And if you want the new text to appear after an older text:

jTextArea.append("Test program");