Question

Fill in the blanks in each of the following statements: a) A JMenuItem that is a JMenu is called a(n) _____________ b) Method _________ attaches a JMenuBar to a JFrame. c) Container class ___________ has a default BoxLayout. d) \(A(n)\) ______________ manages a set of child windows declared with class JInternal Frame.

Short answer

a) Submenu, b) setJMenuBar, c) JOptionPane, d) DesktopManager

Step-by-step solution

Identify Swing Menu Components

The Java Swing library provides a set of 'menu' components that are used to create menu bars, drop-down menus, and menu items. Understanding the terminology and hierarchy of these components will allow us to fill in the blanks correctly.

Fill in Blank (a)

A JMenuItem that is also a JMenu, which can have other JMenuItems as its children, forming a cascading menu, is commonly referred to as a submenu.

Fill in Blank (b)

The method that is used to attach a JMenuBar to a JFrame is setJMenuBar. We use this method to specify the menu bar to be used in a JFrame object.

Fill in Blank (c)

The Container class JOptionPane uses a layout manager that lays out components in a single row or column, which effectively implements the BoxLayout. Therefore, JOptionPane has a default BoxLayout.

Fill in Blank (d)

The desktop manager in Java's Swing library that manages a set of child windows declared with class JInternalFrame is referred to as a DesktopManager.

Key concepts

Understanding JMenuItem in Java Swing

In Java Swing, the JMenuItem is a basic building block used to construct a menu system. This component can represent a single item within a menu, which users can click to perform an action. When we look at complex menu systems, we often find menu items that lead to another list of menu options – these are known as submenus.

Submenus are especially useful when organizing actions that fall into similar categories to avoid overcrowding the main menu bar. In practice, a submenu is an instance of JMenuItem that has been added to a JMenu. This allows hierarchical menu structures, which are easy to navigate and also conserve space within the application's user interface.

Attaching Menus to Frames with setJMenuBar

The setJMenuBar method is critical for integrating a JMenuBar into a JFrame. This function is straightforward: it attaches a fully constructed menu bar to the top of a window or frame where it remains accessible to users.

In usage, one would first create a JMenuBar object, populate it with menus and items, and then bind it to the JFrame using setJMenuBar. This method is called on a JFrame instance and the JMenuBar object is passed as an argument. The intuitive naming of setJMenuBar clearly indicates its purpose, promoting easy readability and maintainability of code.

Laying Out Components with BoxLayout

BoxLayout is a versatile layout manager in Java Swing that aligns components either on a single row (X_AXIS) or a single column (Y_AXIS). Its simplicity makes it perfect for scenarios where you need a straight-line layout.

Although not every Swing container has a default BoxLayout, it is very commonly used within Java Swing for its predictability and ease of use. Creating a BoxLayout involves specifying the container it should manage and the axis along which the components should be laid out. The components in a BoxLayout can be separated with 'struts' and 'glue', giving developers precise control over spacing and alignment.

Managing Multiple Windows with JInternalFrame

The JInternalFrame component is akin to a JFrame, but with a twist: it is designed to exist within another window, often contained by a JDesktopPane. This allows for a multiple-document interface (MDI), where multiple frames can be opened inside a single parent window, each frame acting as an independent subwindow.

These internal frames provide a robust way to manage overlapping windows within an application, usually with features like dragging, resizing, closing, and even minimizing. On a more technical level, a DesktopManager typically manages these internal frames within the desktop pane, dealing with their layout and interaction behavior.