Like putting a Jscrollpane in a Jtextarea?

Question

I’m trying to create a project where I print several sentences in one JTextArea, but for that, I need to include a JScrollPane. I looked at some examples on the internet but none is working.

public class Projeto extends JFrame {

    JPanel painel = new JPanel();
    public static JTextArea textarea = new JTextArea();
    public static JScrollPane sp = new JScrollPane();
    JButton cmd1;

public static void main(String[] args) {
   new Projeto();
}

public Projeto(){
    super("Árvore");
    setResizable(false);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setLocationRelativeTo(null);

    painel.setPreferredSize(new Dimension(600,400));
    painel.setLayout(null);

    cmd1 = new JButton("Start!");
    cmd1.setBounds(450, 50, 100, 30);
    painel.add(cmd1);

    textarea.setBounds(50, 50, 300, 300);
    textarea.setEditable(true);
    sp.add(textarea);

    painel.add(sp);       

    add(painel);
    pack();

    setVisible(true);

    event e = new event();
    cmd1.addActionListener(e);            
}

public static void atualiza(String frase){
    textarea.append(frase);
}   

public class event implements ActionListener{
    Pai p = new Pai();
    public void actionPerformed(ActionEvent e){

        p.start();                       
    }          
}   
}

Answer 1

Define the JTextArea as portview of JScrollPane:

sp.setViewportView(textarea);

A JScrollPane is a flexible container, which adapts as a component added to it. But for this, this component needs to be a viewport of the scrollable panel. This is only possible by passing the component to the panel in its constructor when starting it, or by using the method setViewportView(). The method add does not work properly for this panel in specific.

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A tip:

Avoid using absolute layout, unless it is of extreme necessity and you know the consequences of it, because absolute layout makes it difficult to maintain the screen and makes your application look different depending on the monitor and resolution that is running.

There are several layouts so you don’t have to worry about positioning or manually organizing components. Not to mention that using layouts makes your code easier to maintain than inserting a lot of setbounds, and if you need to change the position of any component, you will have to position all manually.

In its code itself, by using absolute layout, the JTextArea It will never be displayed, because you set a size and position for it, but for the scrollpane there is nothing about its size and position. With the change below, the component is displayed normally:

sp.setBounds(50, 50, 300, 300);
textarea.setEditable(true);
sp.setViewportView(textarea);