JPanel in Java - Swing JPanel Class Explained with Examples

Constructors of JPanel class

JPanel constructors and their descriptions

Methods of JPanel class

getAccessibleContext()

Modifier and Type: AccessibleContext

This retrieves the AccessibleContext linked to this JPanel.

getUI()

Modifier and Type: PanelUI

This method returns the look and feel (L&F) object to render this component.

getUIClassID()

Modifier and Type: String

Specifies the name of the L&F class that creates this component as a string in the response.

paramString()

Modifier and Type: protected String

This method returns a string representation of this JPanel.

setUI(PanelUI ui)

Modifier and Type: void

Sets the look and feel (L&F) object to render this component.

updateUI()

Modifier and Type: void

Resets the UI property to a value from the current look and feel.

Check also Swing component in java

Creating new JPanel

• Typically, creating a new JPanel object is as easy as this:

JPanel Panel = new JPanel();

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• We frequently make a class that extends from JPanel in the following way:

public class Panel extends JPanel {
 
    // code to add components to the panel
 
}

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Setting Layout in Jpanel

• After the panel is built, we can specify a layout manager by calling the method setLayout(LayoutManager). To prevent producing the default FlowLayout object, it is advised to specify the layout manager when creating the panel:
   

// NOT recommended:
JPanel Panel = new JPanel(); // a FlowLayout manager is created by default
Panel.setLayout(new GridBagLayout());
 
// RECOMMENDED:
JPanel Panel = new JPanel(new GridBagLayout());

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• We cannot specify a BoxLayout while establishing the panel since its constructor requires an existing container. For instance:
   

// Exception
JPanel Panel = new JPanel(); // a FlowLayout manager is created by default
Panel.setLayout(new BoxLayout(Panel, BoxLayout.X_AXIS));

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Adding components to JPanel

The add() method adds GUI elements, such as JLabel, JTextField, JButton, etc., to the panel. The add() method comes in various iterations; therefore, the panel's layout manager determines which version should be utilized.

• For the FlowLayout, BoxLayout, GridLayout, or SpringLayout layout managers, use the add(Component) method.
• Use the add(Component comp, Object constraints) method for the following layout managers: CardLayout, GridBagLayout, or BorderLayout.

Customizing appearance for JPanel

A JPanel often doesn't produce its own GUI. However, as needed, we can modify its border, background transparency, and color.

Panel.setBackground(Color.CYAN); // Set background color.
Panel.setOpaque(false);  // make transparent background
//By default, the panel’s background is opaque.
Panel.setBorder(BorderFactory.createBevelBorder(BevelBorder.RAISED));//Set a raised bevel border

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Example

import javax.swing.*;  
import java.awt.*;
import java.awt.event.*;
public class Jpanelex {  
    public static void main (String[]args){
    JFrame frame = new JFrame("Panel demo"); //Create the frame.             
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //Optional:What happens when the frame closes
    frame.setSize(300,300);
    JLabel label = new JLabel("Enter your name");
    JTextField userName = new JTextField(20);
    JPanel Panel= new JPanel();
    JButton buttonLogin = new JButton("Login");
    Panel.add(label);
    Panel.add(userName);
    Panel.add(buttonLogin);
    frame.add(Panel);
    frame.pack();
    frame.setVisible(true);
    }
}

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Output:

Frequently Asked Questions

What is JPanel?

JPanel, a component of the Java Swing package, is a container that can hold a collection of components. JPanel's primary function is to organize elements; numerous layouts can be configured in JPanel to enable better component organization; nevertheless, it lacks a title bar.

What is the use of JPanel?

JPanel's primary function is to arrange components. It has many layouts that may be configured to improve the component organization but lacks a title bar.

Differentiate between JFrame and JPanel.

On the other hand, JFrame typically contains simple window elements like a border, title bar, controls, event handlers, etc. JPanel may be thought of as a universal container that is utilized in case of complicated or more extensive functions that require grouping of numerous components together.

Can we add JPanel in JFrame?

Since JPanel is a subclass of component, it can be used as an argument to any method that accepts Components.

Can we make the background transparent in JPanel?

Yes, we can, with the help of panel.setOpaque(false); By default, the panel's background is opaque.

Conclusion

In this blog, we extensively discussed JPanel, creating them with the help of the JPanel class with suitable examples. We have addressed every detail related to the JPanel class with syntax, constructors, methods, and examples. After learning what JFrame is in java, are you curious to explore more articles on the topic related to the Java programing language? We have you covered.