Java - how to add gui which will make use of initial classes

Question

I've written a standard console application (web scraping) with several classes. The only thing that main fucntion does, is: - create one instance of a class - call one method from created object

Now I need to add the simplest GUI which will contain one button to perform second of those aforementioned actions (call method) and textarea to display everything that NetBeans output shows now.

I created new file with GUI class. It's basically a jFrame with jButton and jTextArea. I managed to get text output to work like I assumed. However I have no idea how to set the button. Netbeans creator redirects me to this part of code:

private void buttonActionPerformed(java.awt.event.ActionEvent evt) {                                       
    // TODO add your handling code here:

    p1.use(); // <<< my initial try
}

where p1 is object created in main class in original file. Netbeans marks "p1" as "cannot find symbol" which is understandable. However, how can I perform such a simple operation? I basically need that Button to push the program forward.

Answer 1

You need to pass the p1 object from your main class into the class for your GUI through a constructor or setter, otherwise it doesn't know what you're trying to access.

For example,

public class MainClass {
    private MyGuiClass gui;
    private P1Class    p1;

    public static void main(String[] args) {
        p1  = new P1Class( /*arguments*/ );
        gui = new MyGuiClass( p1, /*other arguments*/ );
    }
    // Other logic...
}

public class MyGuiClass extends JFrame {
    private P1Class p1;
    public MyGuiClass( P1Class p1, /*other arguments*/ ) {
        this.p1 = p1;
    }
    // Other logic...
}

At this point, you can refer to the p1 object in the rest of your code.

Answer 2

There are many ways to achieve that.

Scenario 1

Make the object p1 accessible to the jFrame object by making it static in the Main class.

public class Main {
    public static P1 p1;

    public static void main(String[] args) {
        p1 = new P1();
        //open window etc.
    }
}

public class MyFrame extends JFrame {
    private void buttonActionPerformed(java.awt.event.ActionEvent evt) {
        // Access object by static reference
        Main.p1.use();
    }
}

Scenario 2

You can pass the object P1 as a parameter to the constructor of your jFrame object.

public class Main {
    public static void main(String[] args) {
        P1 p1 = new P1();
        new MyFrame(p1);
        //open window etc.
    }
}

public class MyFrame extends JFrame {
    private P1 p1;

    public MyFrame(P1 param) {
        // Save object inside the JFrame object
        this.p1 = param;
    }

    private void buttonActionPerformed(java.awt.event.ActionEvent evt) {
        p1.use();
    }
}