如何将信息从一个对象传递到另一个

Question

There's a main JFrame MainPanel using two Internal Frames Read and View , There's a JList of items in Read which is populated by files and a button.

Expected working : Read has a JList populated with files. I'll select a .txt file and press the button and the name of the file (actually I wanted to output the content but let's output the name of the file for simplicity) should be outputted in the JTextArea of View JInternalFrame.

What's Wrong :

1. The View being initialised in MainPanel , can't be reinitialised in Read which pops up the error.
2. If I use View viewPanel = new View() in the Read JInternalFrame's click button event , the JInternalFrame is'nt displayed at all.

MainPanel:

public MainPanel() {
    initComponents();
    pack();
    insert = new Insert();
    view = new View();
    read = new Read();
    jPanel2.add(insert);
    jPanel2.add(view);
    jPanel2.add(read);
    insert.setVisible(true); // Initially only insert is visible later on
    view.setVisible(false);  // I have buttons which set's the view and
    read.setVisible(false);  // read visible

}

Read :

public class Read extends javax.swing.JInternalFrame {
public Read() {
    initComponents();
    pack();
    DefaultListModel model = new DefaultListModel();
    jList1.setModel(model);
    File folder = new File("/home/Naruto/Dattebayo");
    File[] listOfFiles = folder.listFiles();
    for(File file : listOfFiles){
        model.addElement(file.getName());

    }
}

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         

    String selected = (String) jList1.getSelectedValue();

    view.setText(selected); // **Error** 
    view.setVisible(true);  // **View is'nt visible here**
    this.setVisible(false);       
}                                        
}

Answer 1

You ask:

How do I initialize an JInternalFrame from another JInternalFrame?

But your real overall question, in a nutshell is in fact:

How do I pass information from one object to another.

That's it, and really this has little to do with Swing or GUI (for the initial part of my answer), but is rather a basic Java question. The problem you're seeing is that if you create a new View object inside of your Read object, you can change the state of this View instance, but it will have no effect on the visualized View instance because they are two completely unique and distinct objects.

One BAD solution is to make key fields and methods in View static which would allow you to pass information from one object to another using class-level fields and methods, but this breaks OOP design, would increase the cyclomatic complexity of your code making it much harder to debug or to enhance or expand.

A better solution is to simply pass your visualized View instance , the one that is in fact being displayed into the Read instance, and then call methods on it. For example:

public class Read extends javax.swing.JInternalFrame {
    private View view;  // *******

    // give the constructor a View parameter
    public Read(View view) {

        this.view = view; // ***** update the view field

        initComponents();
        pack();
        DefaultListModel model = new DefaultListModel();
        jList1.setModel(model);
        File folder = new File("/home/Naruto/Dattebayo");
        File[] listOfFiles = folder.listFiles();
        for(File file : listOfFiles){
            model.addElement(file.getName());

        }
    }

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         

        String selected = (String) jList1.getSelectedValue();

        // this should work now
        view.setText(selected); 
        view.setVisible(true);  
        this.setVisible(false);       
    }                                        
}

and then pass the view in when both classes are created

public MainPanel() {
    initComponents();
    pack();
    insert = new Insert();
    view = new View();
    read = new Read(view); // *********
    jPanel2.add(insert);
    jPanel2.add(view);
    jPanel2.add(read);
    insert.setVisible(true); // Initially only insert is visible later on
    view.setVisible(false);  // I have buttons which set's the view and
    read.setVisible(false);  // read visible

}

Note that a better overall solution, one that does take into account that yours is a GUI program, is to change the structure of your program to a Model-View-Control, or MVC, structure (I urge you to Google this). The advantage to doing this is that while it would initially seem to increase the complexity of your code, it scales much nicer, and in the long run decreased the code's complexity, greatly decreases coupling and improves cohesion (which is mostly why it reduces complexity) and makes it much easier to debug since your separate parts of the program would be isolated separately testable units.