How do I wait for the input from the GUI back to main?

Question

I want to be able to pass user input from my GUI to one of my classes. However, the input is not passed over and immediately checks the if statement. How do I get program to wait for the input and only checks after the button is clicked?

Main class

public class MainTest {
    public static void main(String[] args) {
        String weaponCategory;
        //Create Java GUI
        GUITest window = new GUITest();

        if(window.getCategory() != "")
        {
            System.out.println("test");
        }
    }

}

GUITest class

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class GUITest implements ActionListener{

    private JFrame frmInventorysystem;
    private JPanel frameBottom;
    private JComboBox equipList;
    private String category = "";
    private JButton confirmBtn, cancelBtn;

    /**
     * Create the application.
     */
    public GUITest() 
    {       
        frmInventorysystem = new JFrame();
        frmInventorysystem.setTitle("InventorySystem");
        frmInventorysystem.setBounds(100, 100, 450, 300);
        frmInventorysystem.getContentPane().setLayout(new BorderLayout(0, 0));

        frmInventorysystem.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        /*JFrame inside another JFrame is not recommended. JPanels are used instead.
        * Creating a flow layout for the bottom frame
        */
        frameBottom = new JPanel();
        frameBottom.setLayout(new FlowLayout());

        //creates comboBox to find out which of the three items player is looking to insert
        String[] weaponCategories = {"Weapon", "Armor", "Mod"};
        equipList = new JComboBox(weaponCategories);
        frmInventorysystem.getContentPane().add(equipList, BorderLayout.NORTH);

        //Converting BorderLayout.south into a flow layout
        frmInventorysystem.getContentPane().add(frameBottom, BorderLayout.SOUTH);

        confirmBtn = new JButton("Confirm");
        confirmBtn.addActionListener(this);

        frameBottom.add(confirmBtn);

        cancelBtn = new JButton("Cancel");
        cancelBtn.addActionListener(this);
        frameBottom.add(cancelBtn);

        frmInventorysystem.setVisible(true);
    }

    public void actionPerformed(ActionEvent e)
    {
        //creates new windows to sort equipment when confirmBtn is clicked
        if(e.getSource() == confirmBtn) 
        {
            if(equipList.getSelectedItem().equals("Weapon"))
            {
                //GUIWeaponCategory weapon = new GUIWeaponCategory();
                category = equipList.getSelectedItem().toString();
            }
        }
        //Exits when cancelBtn is clicked
        if(e.getSource() == cancelBtn)
        {
            System.exit(0);
        }
    }

    public String getCategory()
    {
        return category;
    }

    public void setCategory(String a)
    {
        category = a;
    }
}

GUITest launches as expected. However, the first println is missing. How would I go about doing this? What concepts or pieces of code am I missing?

EDIT1: Added a couple more details to make the program reproducible and complete.

EDIT2: Making the code more readable for easy understanding.

Answer 1

There are some changes to make on your program

1. Remove extends JFrame as stated in my comments above, see Extends JFrame vs. creating it inside the program

2. Place your program on the EDT, see point #3 on this answer and the main method for an example on how to do that.

3. You're confused about how the ActionListeners work, they wait until you perform certain action in your program (i.e. you press Confirm button) and then do something. "Something" in your program means: Print the selected item and check if it's a weapon then, do something else.

So, in this case, you don't need to return back to main to continue with your program, main only serves to initialize your application and nothing else. You need to think in the events and not in a sequential way. That's the tricky and most important part.

You need to change your programming paradigm from console applications and do-while that everything happens in a sequential manner rather than events that are triggered when the user does something with your application.

For example:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class GUITest implements ActionListener {
    private JFrame frmInventorysystem;
    private JPanel frameBottom;
    private JComboBox equipList;
    private JButton confirmBtn, cancelBtn;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new GUITest()); //Java 8+ if using an earlier version check the point #2 in this answer and modify the code accordingly.
    }

    /**
     * Create the application.
     */
    public GUITest() {
        frmInventorysystem = new JFrame();
        frmInventorysystem.setTitle("InventorySystem");
        frmInventorysystem.setBounds(100, 100, 450, 300);
        frmInventorysystem.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frmInventorysystem.getContentPane().setLayout(new BorderLayout(0, 0));

        /*
         * JFrame inside another JFrame is not recommended. JPanels are used instead
         * Creating a flow layout for the bottom frame
         */
        frameBottom = new JPanel();
        frameBottom.setLayout(new FlowLayout());

        // creates comboBox to find out which of the three items player is looking to
        // insert
        String[] weaponCategories = { "Weapon", "Armor", "Mod" };
        equipList = new JComboBox(weaponCategories);
        frmInventorysystem.getContentPane().add(equipList, BorderLayout.NORTH);

        // Converting BorderLayout.south into a flow layout
        frmInventorysystem.getContentPane().add(frameBottom, BorderLayout.SOUTH);

        confirmBtn = new JButton("Confirm");
        confirmBtn.addActionListener(this);

        frameBottom.add(confirmBtn);

        cancelBtn = new JButton("Cancel");
        cancelBtn.addActionListener(this);
        frameBottom.add(cancelBtn);

        frmInventorysystem.setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        // creates new windows to sort equipment when confirmBtn is clicked
        if (e.getSource() == confirmBtn) {
            String category = equipList.getSelectedItem().toString(); //Get the selected category
            doSomething(category); //Pass it as a parameter
        }
        // Exits when cancelBtn is clicked
        if (e.getSource() == cancelBtn) {
            frmInventorysystem.dispose();
        }
    }

    // Do something with the category
    private void doSomething(String selectedEquipment) {
        System.out.println(selectedEquipment);
        if (selectedEquipment.equals("Weapon")) {
            System.out.println("It's a weapon!"); //You can open dialogs or do whatever you need here, not necessarily a print.
        } else {
            System.out.println("Not a weapon");
        }
    }
}

Notice that I removed inheritance, I'm not returning back to main and still printing the selected item and checking if it's a weapon or not.

I also exit the application in a safer way.

This is a sample output:

Weapon
It's a weapon!
Armor
Not a weapon