Java actionPerformed does not add the changed label until the GUI is resized

Question

I am a high school student trying to learn java and any help or advice is appreciated. The code does not set the text after I press the button. The actionPerformed does not do what it is supposed to until I change the size of the GUI for some reason. When I run it and press the button a . pops up but nothing else, if you were to run it then you would see what I am talking about. I think it stops during the action performer for some reason but I am really just guessing. Thank you.

import java.awt.*;
import java.text.DecimalFormat;
import java.text.NumberFormat;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.JFrame;

public class GUI extends JFrame implements ActionListener{
public TextField mpgEnter;
public Label lblResult;
public Button btnEnter;
public TextField gasPriceEnter;
public TextField distanceEnter;
public double mpg;
public double distanceTravel;
double priceOfgas;

public GUI() {


setTitle("GUI Test");



setSize(280, 400);

setDefaultCloseOperation(EXIT_ON_CLOSE);
Label lbl2 = new Label("MPG ||");
add(lbl2);
mpgEnter = new TextField(5);
Label lbl3 = new Label("Price of gas ||");
add(lbl3);
gasPriceEnter = new TextField(5);
Label lbl4 = new Label("Distance");
add(lbl4);
distanceEnter = new TextField(5);
setLayout(new FlowLayout());
add(mpgEnter);
add(gasPriceEnter);
add(distanceEnter);

// add button
btnEnter = new Button("Enter");
btnEnter.addActionListener(this);
add(btnEnter);
//add label


//setResizable(false);
lblResult = new Label("");
add(lblResult);
setVisible(true);
}
public static double calculateGPM(double mpg, double gas,double distance){
    double gasPerMile = gas/mpg;
    double cost1 = gasPerMile * distance;
    NumberFormat formatter = new DecimalFormat("#0.00"); 
    double costFinal = Double.parseDouble(formatter.format(cost1));

    return costFinal;
}
@Override
public void actionPerformed(ActionEvent e) {

    //System.out.print(test.getText());
    mpg = Double.parseDouble(mpgEnter.getText());
    priceOfgas= Double.parseDouble(gasPriceEnter.getText());
    distanceTravel = Double.parseDouble(distanceEnter.getText()); 
    lblResult.setText("The price for your trip is: $" + calculateGPM(mpg, priceOfgas, distanceTravel));
    add(lblResult);

    }
    }

And you fired an event to tell Swing that you are done altering the layout? — Thorbjørn Ravn Andersen, Feb 12 '15 at 21:35
No, the event should be clicking on the button but nothing changes, when I resize it then the label appears. — Aaron Rotem, Feb 12 '15 at 21:38
You are confusing terms. The two kinds of events are different. — Thorbjørn Ravn Andersen, Feb 12 '15 at 21:40

score 1 · Answer 1 · edited May 23 '17 at 10:24

First, you're mixing heavy weight components with light weight components, this is going to cause you no end of issues and is best avoided.

Instead of:

Label use JLabel
TextField use JTextField
Button use JButton

Your primary issue is the fact that your container isn't been updated when the text is changed, this is a limitation of java.awt.Label and simply changing it to javax.swing.JLabel will automatically cause the container to be revalidated once the text of the label has been changed.

See...

for more details

score -1 · Accepted Answer · answered Feb 12 '15 at 21:44

The lblResult label is initialized with "". When you set the value (a large text) there is no room for it inside the flow layout.

I think you must set a more elaborated layout or a minimum width for the result label:

Label width:

  setSize(400, 400);
  lblResult.setPreferredSize(new Dimension(200, 20));

Example Layout:

    final JPanel north = new JPanel(new FlowLayout());
    north.add(mpgEnter);
    north.add(gasPriceEnter);
    north.add(distanceEnter);
    // add button
    btnEnter = new Button("Enter");
    btnEnter.addActionListener(this);
    north.add(btnEnter);
    // add label
    add(north, BorderLayout.NORTH);
    // setResizable(false);
    lblResult = new Label("");
    lblResult.setPreferredSize(new Dimension(200, 20));
    add(lblResult, BorderLayout.CENTER);

Thank you, adding the setPreferredSize fixed the problem, I will try to learn JPanel more and use that next. — Aaron Rotem, Feb 12 '15 at 21:56
[Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?](http://stackoverflow.com/questions/7229226/should-i-avoid-the-use-of-setpreferredmaximumminimumsize-methods-in-java-swi) — MadProgrammer, Feb 12 '15 at 23:18

Java actionPerformed does not add the changed label until the GUI is resized

2 Answers2