JPanel is class of swing package in java and swing package part of j2se to develop standalone application. JPanel is a container and component of the JFrame.

Constructor & Description
1. JPanel()

Creates a JPanel with a double buffer and a flow layout.
2. JPanel(boolean isDoubleBuffered)

Creates a JPanel with FlowLayout and the specified buffering strategy.
3. JPanel(LayoutManager layout)

Create a buffered JPanel with the specified layout manager.
4. JPanel(LayoutManager layout, boolean isDoubleBuffered)

Creates a JPanel with the specified layout manager and buffering strategy.

package com.findnerd;

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

 public class SwingContainerDemo {
   private JFrame mainFrame;
   private JLabel headerLabel;
   private JLabel statusLabel;
   private JPanel controlPanel;
   private JLabel msglabel;

   public SwingContainerDemo(){
    mainFrame = new JFrame("Java Swing Examples");
      mainFrame.setSize(400,400);
      mainFrame.setLayout(new GridLayout(3, 1));
      mainFrame.addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent windowEvent){
            System.exit(0);
         }        
      });    
      headerLabel = new JLabel("", JLabel.CENTER);        
      statusLabel = new JLabel("",JLabel.CENTER);    

      statusLabel.setSize(350,100);

      msglabel = new JLabel("Welcome to Findnerd Blog.", JLabel.CENTER);

      controlPanel = new JPanel();
      controlPanel.setLayout(new FlowLayout());

      mainFrame.add(headerLabel);
      mainFrame.add(controlPanel);
      mainFrame.add(statusLabel);
      mainFrame.setVisible(true);  
   }

   public static void main(String[] args){
      SwingContainerDemo  swingContainerDemo = new SwingContainerDemo();  
      swingContainerDemo.showJPanelDemo();
   }


   private void showJPanelDemo(){
      headerLabel.setText("Container in action: JPanel");      

      JPanel panel = new JPanel();
      panel.setBackground(Color.magenta);
      panel.setLayout(new FlowLayout());        
      panel.add(msglabel);

      controlPanel.add(panel);        
      mainFrame.setVisible(true);      
   }   
 }