Java - Can't update JLabel's text

Question

I have my Store class wherein i could add items to cart then it will increment the cart item number and the total amount.

I also have a view cart button like thing, if it is clicked it will show another frame where the items from the cart shows. When i click remove button from this cart frame i plan to decrement the count and total amount from the previous frame, but the setText method i used in the jLabel where the total price is located don't work.

I call this method from the cart frame then pass the price to be removed whenever i click the remove button

public void updateTotalAmount(double deduct){
    System.out.println("updateTotalAmount - "+deduct);
    tAPriceL.setText(String.valueOf(deduct)); //Total amount price label
    cICountL.setText(String.valueOf(--cICount)); //cart item count label
}

the system.out line is the only statement that works, the rest don't.

when i try to interchange the code like this.

public void updateTotalAmount(double deduct){
    tAPriceL.setText(String.valueOf(deduct)); //Total amount price label
    cICountL.setText(String.valueOf(--cICount)); //cart item count label
    System.out.println("updateTotalAmount - "+deduct);
}

the system.out now didn't work so i guess there is a problem on the setText part.

I can't figure out where is the problem. Could anyone help me with this?

here is the summary of this.. for the main store class.. example i have 5000 worth of items

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class NewClass extends JFrame implements ActionListener {

    JLabel tAPrice = new JLabel("5000");
    JButton viewcart = new JButton("view cart");

    public NewClass() {
        this.setLayout(new FlowLayout());
        add(tAPrice);
        add(viewcart);
        viewcart.addActionListener(this);
    }

    public static void main(String[] args) {
        NewClass n = new NewClass();
        n.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        n.setSize(1150, 730);
        n.setVisible(true);
    }

    public void update(double deduct) {
        System.out.println("updated");
        tAPrice.setText(String.valueOf(Double.parseDouble(tAPrice.getText())
            - deduct));
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == viewcart) {
            Cart2 c = new Cart2();
            c.setVisible(true);
            c.setSize(250, 230);
        }
    }
}

and for the cart class... for example i wanna remove 1000 from the total amount

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;

public class Cart2 extends JFrame implements ActionListener {

    JButton remove = new JButton("remove");

    public Cart2() {
        add(remove);
        remove.addActionListener(this);
    }

    public static void main(String[] args) {
        Cart2 r = new Cart2();
        r.setVisible(true);
        r.setSize(250, 230);
        r.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == remove) {
            NewClass nc = new NewClass();
            nc.update(1000);
        }
    }
}

Answer 1

In Cart2.actionPerformed() you're allocating new NewClass() instead of using the calling instance of NewClass. Try passing instance of NewClass into Cart2 constructor.

For example:

public class Cart2 extends JFrame implements ActionListener {
    JButton remove = new JButton("remove");
    NewClass newClass;

    public Cart2(NewClass newClass) {
        this.newClass = newClass;
        add(remove);

        remove.addActionListener(this);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == remove) {
            // NewClass nc = new NewClass();
            newClass.update(1000);
        }
    }

}

Then in NewClass:

@Override
public void actionPerformed(ActionEvent e) {
    if (e.getSource() == viewcart) {
        Cart2 c = new Cart2(this);
        c.setVisible(true);
        c.setSize(250, 230);
    }
}

Answer 2

• don't use two or more JFrames, not on runtime, this is road to the troubles

• this is job for CardLayout

• put every JComponents to the JPanel, those JPanels put as Cards

• (maybe) then is place for only one JButton for whole GUI