After more than a couple of days I am still unable to populate a text area by going through an array as I can in other languages. I have tried Google, YouTube, stackoverflow, and others and I am still unable to use any examples to help me do this. I have also referenced Java texts. Here is exactly what I am trying to do:
public void getDrinks() {
//System.out.println(theDrinks[arrayCount].toString());
for(int i=0; i<arrayCount; i++) {
area.append(theDrinks[i].toString());
}
}
This code works in other languages but something is wrong with the way I am using the TextArea or the array because I am getting a null pointer. I would love to paste the entire program, but that is not working either. This is the only part that will even remotely paste correctly. Please help me if you can.
You do not, in general, want to use a variable like arrayCount when you can help it. A better version is this:
public void getDrinks() {
for(int i = 0; i < theDrinks.length; i++)
area.append(theDrinks[i].toString());
}
When doing this, it is important to make sure that area has been instantiated already (i.e. it is not null).
If I were implementing this, I would use Java's foreach construct instead, as I find it's a bit more expressive. The following code assumes that theDrinks is an array of Drink objects.
public void getDrinks() {
if(area != null) {
for(Drink drink : theDrinks) {
area.append(drink.toString());
}
}
}
I can't way whay your specific problem can be without more code but here some java code that works.
import java.awt.BorderLayout;
import java.awt.TextArea;
import javax.swing.JFrame;
public class Driver {
public static void main(String[] args) {
// 1. Create the frame.
JFrame frame = new JFrame("FrameDemo");
// 2. Optional: What happens when the frame closes?
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// 3. Create components and put them in the frame.
// ...create emptyLabel...
TextArea area = new TextArea("Area");
frame.getContentPane().add(area, BorderLayout.CENTER);
// 4. Size the frame.
frame.pack();
// 5. Show it.
frame.setVisible(true);
String[] drinks = {"Drink1","Drink2"};
getDrinks(area, drinks);
}
public static void getDrinks(TextArea area, String[] theDrinks) {
// System.out.println(theDrinks[arrayCount].toString());
for (String drink : theDrinks) {
area.append(drink.toString());
}
}
}
Related
What I want to achieve is very simple.
I have 2 classes. "SpeedingTicket" & "SpeedingTicket GUI".
Inside my GUI I have 1 textbox name txtSpeedLimit & a button.
Inside my SpeedingTicket class I have a variable "int speedingTicket".
Inside my SpeedingTicket class I also have a get & set method for "speedingTicket".
I know how to get and set text using JTextFields, but I want to be able to:
receive input from the "txtSpeedLimit", and store that value into the "txtSpeedLimit" instance variable in the "SpeedTicket" class. I can then check for validation etc when I come to adding the vehicle speed.
Maybe this isn't the most efficient way of dealing with this program. Maybe I should scrap the instance variables in SpeedingTicket, and deal with it all in the GUI.
Any advice would be hugely appreciated.
Basically what I'm trying to do is this:
class confirmHandler implements ActionListener{
public void actionPerformed(ActionEvent e){
String val = txtSpeedLimit.getText();
int realNum = speed.getSpeedLimit() = txtSpeedLimit; < but obviously that doesn't work, but I want the textbox link to the variable.
EDIT: If we take away the GUI, all I want my program to do is the following:
Speed Limit: 50 < enterd via textfield
Speed: 60 < entered via textfield
if the speed is blah blah (ive already coded this).. then output a result to one of my labels.
I achieved this without making a GUI and making it only console based, but instead of the user typing it via the console, I want it to be typed via textfields.
THe values that are entered into the textfields should be stored in the two variables (speed and speedlimit) that are in the SpeedingTicket class.
You can update a value in:
public class SpeedingTicket {
int speedingTicket;
public SpeedingTicket() {
speedingTicket = 500;
}
public int getSpeedingTicket() {
return speedingTicket;
}
}
by:
public class SpeedingTicketGUI extends JPanel{
SpeedingTicket st;
SpeedingTicketGUI() {
st = new SpeedingTicket();
setLayout(new FlowLayout(FlowLayout.LEFT));
JTextField txtField = new JTextField(10);
txtField.setText(""+st.getSpeedingTicket());
add(txtField);
JButton btn = new JButton("Update");
btn.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
setSpeedingTicket(txtField.getText());
}
});
add(btn);
}
private void setSpeedingTicket(String text) {
try {
int speedTicket = Integer.parseInt(text);
st.setSpeedingTicket(speedTicket);
System.out.println("Speeding ticket set to " +st.getSpeedingTicket());
} catch (NumberFormatException ex) {
System.out.println("Invalid value " +text);
ex.printStackTrace();
}
}
public static void main(String[] args){
JFrame frame = new JFrame("Speeding Ticket");
frame.setSize(400,100);
frame.add(new SpeedingTicketGUI());
frame.setVisible(true);
}
}
You don't need to store values in JText or any GUI componenets...
Use global static variables. For example:
public static int speed_limit;
You can access this variable from ANY method,class, etc.
There are multiple ways to do it.
You can detect textfield changes by using a DocumentListener or if you want (not recommended) by a KeyListener.
The Listener could be implemented directly by your gui class or by your other class. If you want more abstraction you could implement the DocumentListener by your gui class and create a method
public void addSpeedChangeListener(SpeedChangeListener scl) {
this.speedChangeListeners.add(scl);
}
Your SpeedChangeListener could be very simple:
public interface SpeedChangeListener {
public void speedChanged(int value);
}
Then your second class implements the SpeedChangeListener and calls addSpeedChangeListener(this) on your gui class. Inside the gui class, your document listener calls speedChanged(val) for every listener registered.
EDIT
You can also use the Button and call the speedChanged on every listener inside the actionPerformed method of the ActionListener.
I think it would be easier to use a JOptionDialog which pop ups when the button is clicked. That way you can easily get input and also validate the input straight away.
I am programming an application that deals with orders from a database. It has several pages, a navigation, a header that always should show information about the actual order you are working with and a content area, in which the details of said order get shown:
My MainProgram extends a JFrame and contains a CardLayout, in which the other pages are hosted, so when the user clicks on the page in the navigation, only the view of the content-area changes. Logo, header and the navigation stay the same. The header keeps displaying the order number.
As there are several different pages that contain details about the same order, I need to "send / transfer" information about the order from one page to the other so I can show some information in the header and in the content area from the order object.
But I am not getting this to work as intended, mostly to my misunderstand of static and when to use it, where objects get created exactly and also the complexity of my program: I am using a class that is intended for the navigation and therefore should also handle
the information transfer from one page to the other.
Since I am using a database, creating a MVCE will be hard, so instead I will show the important parts of my program.
MainProgram.java
Here the navigation and the content panel (centerPanel) get created, also the CardLayout. centerPanel and the CardLayout are static, so I can call this from other classes and switch the page that is shown (probably not a good idea?):
NavigationPanel navigationPanel = new NavigationPanel();
public static JPanel centerPanel = new JPanel();
public static CardLayout contentCardsLayout = new CardLayout();
I create the pages and put them into my CardLayout:
OverviewPage overviewPage = new OverviewPage();
BasicDataPage basicDataPage = new BasicDataPage();
centerPanel.setLayout(contentCardsLayout);
overviewPage.setName("overviewPage");
basicDataPage.setName("basicDataPage");
centerPanel.add(overviewPage, "overviewPage");
centerPanel.add(basicDataPage, "basicDataPage");
The main method, where I create a MainProgram object:
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
MainProgram window = new MainProgram();
window.setVisible(true);
window.initialize();
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
OverviewPage.java
The overview page contains a JTable which gets populated from a database. If the user double-clicks an entry, he gets transfered to the BasicDataPage where he can see the details of the order.
But in order to show the details, I need to somehow transfer the information of the order object into the target class and thats the point I am struggling with!
// I tried several things like object into constructor, static object, creating a method etc...
if (mouseEvent.getClickCount() == 2 && row != -1) {
String workNumberOfOrderObject = (String) table.getValueAt(row, 0);
OrderObject orderObject = GetOrderObject.getOrderObjectFromDatabase(workNumberOfOrderObject);
BasicDataPage basicDataPage = new BasicDataPage();
basicDataPage.recieveOrderObject(orderObject);
workNumberPanel.recieveOrderObject(orderObject);
workNumberPanel.setTxtWorkNumber(workNumberOfOrderObject);
MainProgram.contentCardsLayout.show(MainProgram.centerPanel, "basicDataPage");
}
I tried "sending" the order object to the BasicDataPage via the constructor and set the text in the JTextFields in the BasicDataPage accordingly. This did not work, the textfields simply stayed empty altough I can System.out.println(orderObject.toString()) the recieved object.
BasicDataPage.java
I also tried creating a method receiveOrderObject that I use in the OverviewPage, which should set the textfields of the basicDataPage AND the workNumberPanel, but the fields stay empty:
WorkNumberPanel workNumberPanel = new WorkNumberPanel();
JTextField txtCarWidth = new JTextField(TEXTFIELD_LENGTH);
JTextField txtCarDepth = new JTextField(TEXTFIELD_LENGTH);
JTextField txtCarHeight = new JTextField(TEXTFIELD_LENGTH);
public void recieveOrderObject(OrderObject orderObject){
txtCarDepth.setText(orderObject.getCar_depth());
}
Before posting my question I've read several Q/As here on SO like this:
Accessing UUID from another class in Java ... suggesting to use static for global variables.
I know that static variables are class variables, that all instances can use and only one version exists of. So I tried to send a static object from one class to the other.
But since I am using JTextFields, I had to mix static and non-static content, which either did not work at all or the textfields disappeared.
I have the feeling that I am getting a very basic concept in java wrong, so any help, no matter in which direction, is appreciated!
EDIT:
Based on Reşit Dönüks answer, I was able to fill the textfields by making BasicDataPage and loadBasicData(orderObject) in MainProgram static. Now I can do MainProgram.loadBasicData(orderObject); ... and the textfields in the BasicDataPage get filled as intended.
Is this a valid approach or do I get problems for using static for GUI-Elements? ..... Don't!
I realized that, your are creating BasicDataPage in each double click.
if (mouseEvent.getClickCount() == 2 && row != -1) {
String workNumberOfOrderObject = (String) table.getValueAt(row, 0);
OrderObject orderObject = GetOrderObject.getOrderObjectFromDatabase(workNumberOfOrderObject);
BasicDataPage basicDataPage = new BasicDataPage();
This is the main problem. Do not create BasicDataPage there, just reach the created instance and set the order object to that. My solution is below.
public class MainProgram implements OrderView{
//remove statics here
private JPanel centerPanel = new JPanel();
private CardLayout contentCardsLayout = new CardLayout();
private BasicDataPage basicPage;
public MainProgram() {
//other codes
OverviewPage overviewPage = new OverviewPage();
basicPage = new BasicDataPage();
centerPanel.setLayout(contentCardsLayout);
overviewPage.setName("overviewPage");
basicDataPage.setName("basicDataPage");
centerPanel.add(overviewPage, "overviewPage");
centerPanel.add(basicPage, "basicDataPage");
//oher codes
}
#Override
public void loadOrder(OrderObject order) {
basicPage.recieveOrderObject(orderObject);
contentCardsLayout.show(centerPanel, "basicDataPage");
}
}
public interface OrderView {
public void loadOrder(OrderObject order);
}
public class OverviewPage {
OrderView orderView;
public OverviewPage(OrderView orderView) {
this.orderView = orderView;
}
//in ActionPerformed
if (mouseEvent.getClickCount() == 2 && row != -1) {
String workNumberOfOrderObject = (String) table.getValueAt(row, 0);
OrderObject orderObject = GetOrderObject.getOrderObjectFromDatabase(workNumberOfOrderObject);
orderView.loadOrder(orderObject);
workNumberPanel.recieveOrderObject(orderObject);
workNumberPanel.setTxtWorkNumber(workNumberOfOrderObject);
}
}
As pointed already, Singleton is the way to go. I would just like to point out a mistake in the code provided in the answer before.
private static MainFrameinstance = null;
Rename MainFrameinstance to instance or vice-versa; because the same variable is checked by the getInstance() method.
I'm very new to Java and I'm setting myself the challenge on writing a Caesar shift cipher decoder. I'm basically trying to clear a JTextArea from another class. I have two classes, a GUI class called CrackerGUI and a shift class. The JtextArea is in the GUI class along with the following method:
public void setPlainTextBox(String text)
{
plainTextBox.setText(text);
}
The GUI class also has a clear button with the following:
private void btnClearActionPerformed(java.awt.event.ActionEvent evt) {
Shift classShift = new Shift();
classShift.btnClear();
}
Lastly i have the method in the shift class to clear the JTextArea.
public class Shift extends CrackerGUI {
public void btnClear()
{
CrackerGUI gui = new CrackerGUI();
gui.setPlainText(" ");
System.out.println("testing");
}
}
The testing text is printing out to console but the JTextArea wont clear. I'm not sure as to why :). I am sure it's a very simple mistake but it has me baffled. Any help would be appreciated.
Thank you in advance.
You're misusing inheritance to solve a problem that doesn't involve inheritance. Don't have Shift extend CrackerGUI and don't create a new CrackerGUI object inside of the btnClear() method since neither CrackerGUi is the one that's displayed. Instead have Shift hold a reference to the displayed CrackerGUI object and have it call a public method of this object.
e.g.,
public class Shift {
private CrackerGUI gui;
// pass in a reference to the displayed CrackerGUI object
public Shift(CrackerGUI gui) {
this.gui = gui;
}
public void btnClear() {
//CrackerGUI gui = new CrackerGUI();
gui.setPlainText(" ");
System.out.println("testing");
}
}
You also should probably not be creating new Shift objects in your GUI's actionPerformed methods, but rather use only one Shift object that is a class field.
The btnClear method clears the text area of a new CrackerGUI instance. It's like if you wanted to clear a drawing on a sheet of paper by taking a new blank sheet and clearing it. The original sheet of paper will keep its drawing.
You need to pass the gui instance to your Shift:
public class Shift {
private CrackerGUI gui;
public Shift(CrackerGUI gui) {
this.gui = gui;
}
public void btnClear() {
this.gui.setPlainText(" ");
}
}
and in the CrackerGUI class :
private void btnClearActionPerformed(java.awt.event.ActionEvent evt) {
Shift classShift = new Shift(this);
classShift.btnClear();
}
Assuming CrackerGUI is your GUI, you should have the following instead:
public class CrackerGUI {
public void setPlainTextBox(String text)
{
plainTextBox.setText(text);
}
public void btnClear()
{
setPlainTextBox("");
System.out.println("testing");
}
}
One last thing, never make your GUI elements public! You should ask the GUI to clear itself and leave that knowledge of clearing elements hidden inside it.
You could try using static methods, as you would end up creating a new gui, then displaying that one, in stead of the current one already displayed.
This would require the parent class to be static too, which may cause errors in some of your methods, just a heads up.
Or else, you could create your own setText method:
void setText(JTextField t, String s){
t.setText(s);
}
that may enable you to directly edit components in the current GUI.
I can't .setText(...) for a JTextField outside of the class that creates the gui. I'm very confused and I feel like there is something basic I am missing. I need some help here.
Here is what I am doing:
In a class (called MainClass) I create an instance of a class that creates my gui
TestText gui = new TestText();
with a constructor that sets the default settings (a JTextField and a button with a listener). Then I call the a setter that I wrote, where I pass it a string that is to set the text of the JTextField:
gui.setText("new");
But "new" doesn't show up on the gui.
I know my setter works from within the class because if I make a call to the setter from the button that I created in gui then the changes show up on the gui.
The part that really confuses me is this: If I call my getter just before my setter, then it returns the old value. Then if I call the getter again after I call the setter then it returns the new value, while the gui continues to show the old value. I thought that maybe it just isn't repainting the gui so I tried all kinds of permutations of .invalidate(), .validate(), .update() and .repaint(), all from the MainClass and from inside the setter. But none did anything.
Is it possible that I somehow have 2 different instances of the gui and I'm only editing one of them?
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class TestText {
private JTextField textField;
private JButton button;
private JPanel frame;
JFrame jFrame;
public void setText(String text) {
textField.setText(text);
}
public String getText() {
return textField.getText();
}
public TestText() {
this.textField.setText("98.6");
this.jFrame = new JFrame("TestText");
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
setText("new (button)");
}
});
}
public void setData(TestText data) {
data.setText("new (setData)");
}
public void getData(TestText data) {
}
public boolean isModified(TestText data) {
return false;
}
public void createGui(String[] args) {
jFrame.setContentPane(new TestText().frame);
jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
jFrame.pack();
jFrame.setVisible(true);
}
}
and then here's the main class that I'm trying to create the gui from:
public class MainClass {
public static void main(String[] args) {
TestText gui = new TestText();
gui.createGui(null);
System.out.println(gui.getText());
gui.setData(gui);
System.out.println(gui.getText());
gui.setText("new (MainClass)");
System.out.println(gui.getText());
}
}
It looks like you're missing the reference to the text field I think...
gui.referenceToTextField.setText("new word");
EDIT: Very nice SSCCE! However, there are several problems (not in the order provided, necessarily).
You are overriding the setText() method. Don't do this unless you want the method to do something different—why you would want to do this I have no idea.
You aren't even using the args array in the createGui() method. You can create methods without specifying any parameters/arguments.
The getData() method is, right now, useless (If I were you, given what you're trying to accomplish, I would remove the method entirely). I'm assuming, from the apt method name (another good thing to do), that you want to retrieve the data from the text field. Put this line inside the method (and change the word void to String) and you should be set!
return textField.getText();
Truthfully, this shouldn't even run due to a NullPointerException. You aren't initializing any of the components other than the JFrame. You need to do things like textField = new JTextField(20).
Even if you could run this, the button wouldn't work at all because the button hasn't been told that it does anything. To do this call button.addActionListener() with the name of the listening class as the argument. If the GUI and listening classes happen to be in one class together (like I will show you in a minute), the argument is simply this.
You aren't adding any components to the frame. For every component you wish to put into your frame, you must call add(Component cmpt).
Having said this, I think I'm just going to try to recreate what you're trying to do here into one class. You don't really need two separate classes unless the listening portion is excessively long.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class TestText extends JFrame implements ActionListener {
JTextField textField = new JTextField(20);
JButton set = new JButton("Set Text");
JButton get = new JButton("Get Text");
public TestText() {
super();
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
add(textField);
set.addActionListener(this); //this tells the program that the button actually triggers an event
add(set);
get.addActionListener(this);
add(get);
pack();
setVisible(true);
}
public void actionPerformed(ActionEvent event) {
if (event.getSource() == set) {
textField.setText(JOptionPane.showInputDialog(null, "Enter a new word for the text field:"));
} else {
System.out.println(textField.getText());
}
}
public static void main(String[] args) {
TestText tt = new TestText();
}
}
After doing some reading I think it is due to my code not accessing the Event Dispatch Thread like #camickr suggested. Here is some documentation that helped me solve my problem.
I'm trying to create a blackjack program for my final project in Java. I'm still very new to Java and OOD so I apologize if my problem seems very trivial to you :(
How my program works: I have three classes so far.
main.java
This class builds my frame and runs all the other methods.
cards.java
This class creates an array that holds the card values and location to picture. I have a for loop in there that auto-populates it.
hits.java
This class is meant to "randomly" generate a number that will represent the chosen card. The way this works is by taking the randomly created int and pointing it to a matching index location on the array.
I assign the value to string objects that I then try to add to a jlabel and then add that jlabel to my main frame. The code is as follows:
hits.java
// Import necessary classes.
import java.util.Random;
public class hits {
// Create random object.
Random rand = new Random();
// Declare variables.
int card;
String cardVal, cardPic;
// Instantiate the needed classes.
main s = new main();
cards t = new cards();
// Constructor for the class.
public hits() {
// Randomly generate a number (0 - 9).
card = rand.nextInt(10);
// Populate the array.
t.runCards();
// Assign the cards according to the num. generated.
cardVal = t.deck[card][0];
cardPic = t.deck[card][1];
}
// Run Method
public void runHits() {
// Add the card chosen to the GUI.
s.a.setText("hello");
s.dealerCards.add(s.a);
}
}
I have "hello" as the text for the label because I wanted to see if perhaps my array was not populating, but even that doesn't work. If it helps here is my main.java as well (constructor and main method):
// Constructor for the main class.
public main() {
// Setup the MAIN container.
f1.getContentPane().setLayout(new GridLayout(0, 1));
f1.setSize(200, 200);
f1.add(dealerName);
f1.add(dealerCards);
f1.add(userCards);
f1.add(userName);
// Setup the inner panels.
dealerCards.setLayout(new GridLayout(1, 2));
dealerCards.add(b);
userCards.setLayout(new GridLayout(1, 6));
userCards.add(c);
userCards.add(d);
}
// Build the frame.
public void GUILaunch() {
// Display Frame
f1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f1.setVisible(true);
}
// Main method.
public static void main(String args[]) {
// Distribute the dealer's/player's starting hands.
hits deal = new hits();
deal.runHits();
// Launch the GUI
main gui = new main();
gui.GUILaunch();
}
Hopefully I have provided enough information to help you understand what's going on here. So to sum it all up: how can i add my jlabel(from another class) holding the randomly selected card to my main frame
Thanks in advance.
The deal.runHits() adds a label to the Main object that deal owns rather than the gui object.
I would suggest the following :
Make your main class have an instance of hits and hits have an instance of the cards object...
so you get something like this
public class main {
private hits hits_instance
//constructor
main(){ hits_instance = new hits(); }
//this method will add your cards
public void addCards(){
// frame = whatever frame you are using
frame.add(hits_instance.getCards());
}
}
public class hits {
private cards cards_instance;
hits(){ cards_instance= new cards();}
public JLabel getCards() {return cards_instance.getCard(randomNumber);}
}