Thread: Place form in center of screen

My form is wedged against the NW corner of my screen; I want it in the middle. In fact, I will always want the main form (in every project) in the middle. How can I make that the default behavior?

I found this on a similar thread:

Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
int left = (d.width - this.getWidth()) / 2;
int top = (d.height - this.getHeight()) / 2;
this.setLocation(left, top);

but the "getX()" are not recognized. Do I need an import statement to get it to work? I currently have io, net, swing, awt, and awtevent

Do I need an import statement to get it to work?

An import statement is used by the compiler to find a class definition. It specifies a package that contains classes that are being used in the program.
It is not involved with locating methods for a class.

For your posted code, what class is represented by "this"? Is the code in a method in an instance of a class or in the static main method?

Why reinvent the wheel?

// center frame on screen
frame.setLocationRelativeTo(null);

What getX? I don't see this in the code you posted.

By "getX()" I meant getWidth() and getHeight().

The code snippet above won't compile; I get,

"Description Resource Path Location Type
The method getHeight() is undefined for the type RTTCPSortSimMain RTTCPSortSimMain.java /RT_TCP_SortSimUtil/src line 48 Java Problem"

(and similar err msgs for getWidth() and setLocation().

I also tried this:

//frame.setLocationRelativeTo(null); <- by default, it sits NW, but this sends it SE

what class is represented by "this"? Is the code in a method in an instance of a class or in the static main method?

Originally Posted by Norm

For your posted code, what class is represented by "this"? Is the code in a method in an instance of a class or in the static main method?

It is in "go":

public static void main(String[] args) {
new RTTCPSortSimMain().go();
}

public void go() {
// here is where the previously posted code lives

...

what class is represented by "this"?
What class is go in? What Java class is extended by RTTCPSortSimMain?

Originally Posted by Blackbird

I also tried this:

//frame.setLocationRelativeTo(null); <- by default, it sits NW, but this sends it SE

If you want any more help, you're going to have to tell us what class you're using for 'frame' and what the environment is. The stuff you've been given works fine on standard Java frames & windows in a normal environment.

sends it SE

I noticed that happening when I hadn't set the size yet. The upper left corner of the frame was centered. Because the frame had a size of 0,0.
Giving the frame a size centered it as expected.

Originally Posted by Norm

I noticed that happening when I hadn't set the size yet. The upper left corner of the frame was centered. Because the frame had a size of 0,0.
Giving the frame a size centered it as expected.

I imagine it must be difficult to position an object that has no size!

Originally Posted by dlorde

If you want any more help, you're going to have to tell us what class you're using for 'frame' and what the environment is. The stuff you've been given works fine on standard Java frames & windows in a normal environment.

I guess I'm new enough that I don't understand the question, so I'll just provide the entire class:

package com.jcp.tds;

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

public class RTTCPSortSimMain {

JTextArea incoming;
JTextArea outgoing;
JTextField tfHost1;
JTextField tfHost2;
JTextField tfPort1;
JTextField tfPort2;
JLabel lblHost1;
JLabel lblHost2;
JLabel lblPort1;
JLabel lblPort2;
JLabel lblSent;
JLabel lblReceived;
BufferedReader reader;
PrintWriter writer;
Socket sock;
/**
* @param args
*/
public static void main(String[] args) {
new RTTCPSortSimMain().go();
}

public void go() {
JFrame frame = new JFrame("JCP TDS RT TCP Util (AKA 'Fred')");
JPanel mainPanel = new JPanel();

// The "Send" (contents from file) TextArea
outgoing = new JTextArea(15, 50);
outgoing.setLineWrap(true);
outgoing.setWrapStyleWord(true);
outgoing.setEditable(false); // should this be true for outgoing?
JScrollPane qScrollerOutgoing = new JScrollPane(outgoing);
qScrollerOutgoing.setVerticalScrollBarPolicy(Scrol lPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
qScrollerOutgoing.setHorizontalScrollBarPolicy(Scr ollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);

// The "Receive" (contents from remote machine) TextArea
incoming = new JTextArea(15, 50);
incoming.setLineWrap(true);
incoming.setWrapStyleWord(true);
incoming.setEditable(false);
JScrollPane qScrollerIncoming = new JScrollPane(incoming);
qScrollerIncoming.setVerticalScrollBarPolicy(Scrol lPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
qScrollerIncoming.setHorizontalScrollBarPolicy(Scr ollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);

JButton sendButton = new JButton("Send and Receive");
sendButton.addActionListener(new SendButtonListener());

tfHost1 = new JTextField(16); //might replace the IP Address hosts w. combo boxes later
tfHost2 = new JTextField(16);
tfPort1 = new JTextField(4);
tfPort2 = new JTextField(4);
lblHost1 = new JLabel("Host 1 (Dispatch) - IP Address:");
lblHost2 = new JLabel("Host 2 (Disposition) - IP Address:");
lblPort1 = new JLabel("Port 1");
lblPort2 = new JLabel("Port 2");
lblSent = new JLabel("Sent");
lblReceived = new JLabel("Received");

mainPanel.add(lblHost1);
mainPanel.add(tfHost1);
mainPanel.add(lblPort1);
mainPanel.add(tfPort1);

mainPanel.add(lblHost2);
mainPanel.add(tfHost2);
mainPanel.add(lblPort2);
mainPanel.add(tfPort2);
mainPanel.add(sendButton);
mainPanel.add(lblSent);
mainPanel.add(qScrollerOutgoing);
mainPanel.add(lblReceived);
mainPanel.add(qScrollerIncoming);

frame.getContentPane().add(BorderLayout.CENTER, mainPanel);

//frame.setLocationRelativeTo(null); <- by default, it sits NW, but this sends it SE

// Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
// int left = (d.width - this.getWidth()) / 2;
// int top = (d.height - this.getHeight()) / 2;
// this.setLocation(left, top);

setUpNetworking();

Thread readerThread = new Thread(new IncomingReader());
readerThread.start();

frame.setSize(640, 800); // width, height
frame.setVisible(true);
}

private void setUpNetworking() {
try {
sock = new Socket("127.0.0.1", 5000);
InputStreamReader streamReader = new InputStreamReader(sock.getInputStream());
reader = new BufferedReader(streamReader);
writer = new PrintWriter(sock.getOutputStream());
System.out.println("networking established");
}
catch(IOException ex)
{
ex.printStackTrace();
}
}

public class SendButtonListener implements ActionListener {
@Override
public void actionPerformed(ActionEvent ev) {
try {
writer.println(outgoing.getText());
writer.flush();

}
catch (Exception ex) {
ex.printStackTrace();
}
outgoing.setText("");
outgoing.requestFocus();
}
}

class IncomingReader implements Runnable {
@Override
public void run() {
String message;
try {
while ((message = reader.readLine()) != null) {
System.out.println("client read " + message);
incoming.append(message + "\n");
}
} catch (IOException ex)
{
ex.printStackTrace();
}
}
}

}

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Did you see post#11 setSize before setting location.

Okay, one of the replies here gave me a clue: I had to move the code in question AFTER the "setSize()" for it to work. Now the sun is shining, the birds are singing again, &c.

frame.setSize(640, 800); // width, height
frame.setLocationRelativeTo(null);
frame.setVisible(true);