So the buttons you click to install the app, change volume, etc form the GUI. Without it, the user cannot interact with the raw code working behind the scene. So you can think of the GUI as an insulator around the live code.

AWT is short for Abstract Windowing Toolkit. The AWT is the bedrock upon which other API’s of the JFC are built. The AWT allows Java programmers to write applications and applets that interact with the user through windows and other GUI components.

The AWT doesn’t draw GUI components itself. That’s, the components such as buttons the user interact with are not directly built by the AWT classes. The AWT classes rather interact with another layer of classes called the Peer classes and direct these peer Classes to instruct the underlining operating system to draw the GUI components.

Now, let’s put this simple. Suppose you’re using a Windows Operating system. If you are using an application built with the AWT, then the components you’re seeing aren’t drawn by the AWT itself. They’re rather drawn on the screen by the Windows Operating system classes responsible for drawing graphics on the screen.

 However, AWT will be the API passing instructions to the Windows classes through another layer of software called the Peer classes.

 This might look like a smart process but it’s not without its problems.

AWT components are called heavyweight components because they rely on peer Classes of the underlying operating system. Because it always needs these peer Classes to function, it makes the AWT “heavy”.

Java2D is built upon the AWT. It expands on the graphics functionalities in Java 1.0 and Java 1.1.

Java 2D is the name for the state-of-the-art two-dimensional graphics API introduced in Java 1.2. Java 2D is built upon the AWT, but greatly expands on the graphics capabilities that were available in Java 1.0 and Java 1.1.

 Java 2D includes support for resolution independence, rotation, scaling and shearing of arbitrary graphics, antialiasing of text and graphics, alpha transparency, color compositing, and the use of the full range of fonts installed on the native system.

Java2D is built upon the AWT. It expands on the graphics functionalities in Java 1.0 and Java 1.1. 

Java 2D is the name for the state-of-the-art two-dimensional graphics API introduced in Java 1.2. Java 2D is built upon the AWT, but greatly expands on the graphics capabilities that were available in Java 1.0 and Java 1.1.

Java 2D includes support for resolution independence, rotation, scaling and shearing of arbitrary graphics, antialiasing of text and graphics, alpha transparency, color compositing, and the use of the full range of fonts installed on the native system.

Swing is a GUI API. It has a lot of classes for creating graphical user interface. Swing is an alternative for AWT. It’s more powerful and versatile. Few of the classes in swing rely on the underlining classes of the Operating system.

Most of the swing classes draw graphic components on their own unlike the AWT which always depend on third-party classes of the native OS. 

Swing was released to remedy the major problems posed by the use of the AWT.

Unlike the AWT, Swing components can be easily customized.

They can have the same “look and feel” across different Operating systems because they don’t rely on these Operating systems to create its graphics.

Swing components are called lightweight components. This is because with the exception of few, majority of its classes don’t need any peer Classes. This makes them “light”, hence, lightweight.