从另一个类更改JTextArea值

Question

How to allow another class to modify JTextArea from another class?

For example, let's say I have 2 classes:

Panel.java

public class Panel extends JPanel
{
    private JTextArea instructions;

    public Panel()
    {
        instructions = new JTextArea(15,15);
        add(instructions);
    }
}

MenuBar.java

public class MenuBar extends JMenuBar
{
    private JMenuItem openMenuItem,;

    public MenuBar()
    {
        JMenu fileMenu = new JMenu("File");
        openMenuItem = new JMenuItem("Open");
        fileMenu.add(openMenuItem);
        add(fileMenu);

        MenuListener listener = new MenuListener();
        openMenuItem.addActionListener(listener);
    }

    private class MenuListener implements ActionListener
    {
        public void actionPerformed(ActionEvent event)
        {
            if( event.getSource() == openMenuItem )
            {
                // change value of JTextArea from Panel.java
            }
        }
    }
}

How can I modify instructions JTextArea (Panel.java) from MenuBar.class?

Answer 1

First of all, the code snippet of MenuBar doesn't compile because of a comma in following line:

private JMenuItem openMenuItem,;

Now you have a class attribute instructions which is a JTextArea object in the class Panel. This is private so only the class Panel can reach it, which is good. If you want to get or set the value of that property by another class, you can add a getter/setter for it.

In Panel add following code:

public void setInstructions(JTextArea instructions) {
        this.instructions = instructions;
    }

    public JTextArea getInstructions() {
        return instructions;
    }

setInstructions is the method where you are looking for, you can set the instruction TextArea with the value you pass by as parameter.

please modify the private class in MenuBarwith following code to show what I mean.

private class MenuListener implements ActionListener
    {
        public void actionPerformed(ActionEvent event)
        {
            if( event.getSource() == openMenuItem )
            {
                Panel panel = new Panel(); //I don't know where you get your panel data from so I create a new one
                panel.setInstructions(new JTextArea("I'm a text area and I have instructions")); //set the JTextArea value

                System.out.println(panel.getInstructions().getText()); //test print to show how you can get the JTextArea text
            }
        }
    }

I also added a test print to validate the setter works.