Whenever you create a graphical user interface with Java Swing functionality, you will need a container for your application. In the case of Swing, this container is called a JFrame. All GUI applications require a JFrame. In fact, some Applets even use a JFrame. Why?
You can't build a house without a foundation. The same is true in Java: Without a container in which to put all other elements, you won't have a GUI application. In other words, the JFrame is required as the foundation or base container for all other graphical components.
Java Swing applications can be run on any system that supports Java. These applications are lightweight. This means that don't take up much space or use many system resources.
JFrame is a class in Java and has its own methods and constructors. Methods are functions that impact the JFrame, such as setting the size or visibility. Constructors are run when the instance is created: One constructor can create a blank JFrame, while another can create it with a default title.
When a new JFrame is created, you actually create an instance of the JFrame class. You can create an empty one, or one with a title. If you pass a string into the constructor, a title is created as follows:
JFrame f = new JFrame();
// Or overload the constructor and give it a title:
JFrame f2 = new JFrame("The Twilight Zone");