I design a JPanel using Netbeans Builder.I copied the source code and use it in this class.I also add a main method with a constructor.Run the file , builds succesfully but Java VM doest open any gui. Here s the whole code.
import java.awt.Dimension;
import javax.swing.*;
/**
*
* @author Fotis
*/
public class Gui extends javax.swing.JPanel {
public javax.swing.JButton exitBtn;
public javax.swing.JTextArea filePreviewArea;
public javax.swing.JList folderList;
public javax.swing.JPanel jPanel1;
public javax.swing.JPanel jPanel2;
public javax.swing.JScrollPane jScrollPane1;
public javax.swing.JScrollPane jScrollPane2;
public javax.swing.JButton openFileBtn;
public javax.swing.JButton openFolderBtn;
public javax.swing.JLabel welcomeLabel;
/**
* Creates new form Gui
*/
public static void main (String[] args){
Gui a=new Gui();
a.createGui();
a.setPreferredSize(new Dimension(800,600));
}
@SuppressWarnings("unchecked")
public void createGui() {
jPanel1 = new javax.swing.JPanel();
welcomeLabel = new javax.swing.JLabel();
openFolderBtn = new javax.swing.JButton();
exitBtn = new javax.swing.JButton();
openFileBtn = new javax.swing.JButton();
jPanel2 = new javax.swing.JPanel();
jScrollPane1 = new javax.swing.JScrollPane();
filePreviewArea = new javax.swing.JTextArea();
jScrollPane2 = new javax.swing.JScrollPane();
folderList = new javax.swing.JList();
jPanel1.setMaximumSize(new java.awt.Dimension(32767, 60));
jPanel1.setMinimumSize(new java.awt.Dimension(800, 60));
jPanel1.setPreferredSize(new java.awt.Dimension(800, 60));
welcomeLabel.setText("Welcome to Alpha Reader.Choose a single file or a folder.");
openFolderBtn.setLabel("Open Folder");
openFolderBtn.setPreferredSize(new java.awt.Dimension(100, 32));
exitBtn.setLabel("Exit");
exitBtn.setName(""); // NOI18N
exitBtn.setPreferredSize(new java.awt.Dimension(100, 32));
openFileBtn.setLabel("Open File");
openFileBtn.setMaximumSize(new java.awt.Dimension(100, 32));
openFileBtn.setMinimumSize(new java.awt.Dimension(100, 32));
openFileBtn.setPreferredSize(new java.awt.Dimension(100, 32));
javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
jPanel1.setLayout(jPanel1Layout);
jPanel1Layout.setHorizontalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addGap(34, 34, 34)
.addComponent(welcomeLabel, javax.swing.GroupLayout.PREFERRED_SIZE, 300, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 60, Short.MAX_VALUE)
.addComponent(openFileBtn, javax.swing.GroupLayout.PREFERRED_SIZE, 120, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(18, 18, 18)
.addComponent(openFolderBtn, javax.swing.GroupLayout.PREFERRED_SIZE, 120, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(18, 18, 18)
.addComponent(exitBtn, javax.swing.GroupLayout.PREFERRED_SIZE, 120, javax.swing.GroupLayout.PREFERRED_SIZE)
.addContainerGap())
);
jPanel1Layout.setVerticalGroup(
jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel1Layout.createSequentialGroup()
.addContainerGap()
.addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(welcomeLabel, javax.swing.GroupLayout.PREFERRED_SIZE, 32, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(openFolderBtn, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(exitBtn, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(openFileBtn, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addContainerGap(16, Short.MAX_VALUE))
);
welcomeLabel.getAccessibleContext().setAccessibleName("WelcomeLabel");
welcomeLabel.getAccessibleContext().setAccessibleDescription("");
openFolderBtn.getAccessibleContext().setAccessibleName("openFolderBtn");
exitBtn.getAccessibleContext().setAccessibleName("exitBtn");
openFileBtn.getAccessibleContext().setAccessibleName("openBtn");
jPanel2.setMinimumSize(new java.awt.Dimension(800, 100));
jPanel2.setPreferredSize(new java.awt.Dimension(800, 536));
filePreviewArea.setColumns(20);
filePreviewArea.setRows(5);
jScrollPane1.setViewportView(filePreviewArea);
folderList.setModel(new javax.swing.AbstractListModel() {
String[] strings = { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" };
public int getSize() { return strings.length; }
public Object getElementAt(int i) { return strings[i]; }
});
jScrollPane2.setViewportView(folderList);
folderList.getAccessibleContext().setAccessibleName("folderList");
javax.swing.GroupLayout jPanel2Layout = new javax.swing.GroupLayout(jPanel2);
jPanel2.setLayout(jPanel2Layout);
jPanel2Layout.setHorizontalGroup(
jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel2Layout.createSequentialGroup()
.addContainerGap()
.addComponent(jScrollPane2)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 500, javax.swing.GroupLayout.PREFERRED_SIZE)
.addContainerGap())
);
jPanel2Layout.setVerticalGroup(
jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel2Layout.createSequentialGroup()
.addContainerGap()
.addGroup(jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
.addComponent(jScrollPane2, javax.swing.GroupLayout.DEFAULT_SIZE, 514, Short.MAX_VALUE)
.addComponent(jScrollPane1))
.addContainerGap())
);
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
this.setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(jPanel2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(jPanel2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(0, 32, Short.MAX_VALUE))
);
jPanel1.getAccessibleContext().setAccessibleName("");
jPanel1.getAccessibleContext().setAccessibleDescription("");
}
}
JPanel extends JComponent.
In the documentation of JComponent, it is written that:
The base class for all Swing components except top-level containers.
To use a component that inherits fromJComponent, you must place the component in a containment hierarchy whose root is a top-level Swing container.
The top-level Swing container means either a JFrame or a JApplet.
Hence, you need one of these to show your GUI.
For more info, you can visit: https://docs.oracle.com/javase/tutorial/uiswing/components/toplevel.html