Question

Determine whether each statement is true or \(f a l\) se. If false , explain why. a) Only one layout manager can be used per Container. b) GUI components can be added to a Container in any order in a BorderLayout. c) JRadioButtons provide a series of mutually exclusive options (i.e., only one can be true at a time) d) Graphics method setFont is used to set the font for text fields. e) A JList displays a scrollbar if there are more items in the list than can be displayed. f) A Mouse object has a method called mouseDragged.

Short answer

a) True, b) False, c) True, d) False, e) False, f) False.

Step-by-step solution

Evaluate Statement A

Statement A is: "Only one layout manager can be used per Container." In Java Swing, each Container can have only one LayoutManager at a time, but it is possible to change the LayoutManager of a Container during the program execution. However, at any given moment, only one LayoutManager is active. Thus, this statement is true.

Evaluate Statement B

Statement B is: "GUI components can be added to a Container in any order in a BorderLayout." In BorderLayout, the order of adding components matters because each component is defined by its position (e.g., NORTH, SOUTH, EAST, WEST, CENTER). If two components are added to the same position consecutively, the first one will be replaced. This statement is false.

Evaluate Statement C

Statement C is: "JRadioButtons provide a series of mutually exclusive options (i.e., only one can be true at a time)." JRadioButtons are typically used within a ButtonGroup in Swing to enforce mutual exclusiveness. When used this way, only one JRadioButton in the group may be selected at a time. Therefore, this statement is true.

Evaluate Statement D

Statement D is: "Graphics method setFont is used to set the font for text fields." The setFont method of the Graphics class sets the font for drawing text in a context, but for changing the font of a text field in Swing, you use the setFont method of the text component (e.g., JTextField). Thus, this statement is false.

Evaluate Statement E

Statement E is: "A JList displays a scrollbar if there are more items in the list than can be displayed." By default, a JList does not automatically display scrollbars. It must be added to a JScrollPane to enable scrolling functionality when the list contains more items than can be initially shown. Therefore, this statement is false.

Evaluate Statement F

Statement F is: "A Mouse object has a method called mouseDragged." In Java, mouse event handling is done through listener interfaces, such as MouseListener and MouseMotionListener. The method mouseDragged is indeed part of the MouseMotionListener interface, not of a Mouse object itself. Hence, this statement is false.

Key concepts

Swing LayoutManager

In Java GUI programming, particularly using Swing, the LayoutManager is crucial for defining how components are arranged within a container.
Every container has only one active LayoutManager at any given time. However, you can swap this out during the application's runtime if needed. Here’s what this means in practice:

• Each container like JFrame or JPanel can utilize various LayoutManagers such as BorderLayout, FlowLayout, or GridLayout, among others.
• By changing the LayoutManager, you alter the way components within the container are organized.
• For instance, you might start with a FlowLayout during the initial design and later switch to a GridLayout if requirements change.

Remember, while only one LayoutManager is active at any moment, adapting and transitioning between different LayoutManagers can greatly enhance the flexibility of your interface design.

JRadioButton exclusivity

JRadioButtons are used in Java GUI for allowing users to make a choice among multiple options.
But how do they ensure that only one option can be selected at a time? By grouping them into a ButtonGroup!

• A ButtonGroup enforces that only one JRadioButton in the group can be selected at any time, ensuring mutual exclusivity.
• Think of a ButtonGroup as a tie that binds related radio buttons together, thus managing their state.
• This is perfect for single-choice scenarios like selecting a "Yes/No" answer or choosing favorite colors where only one can be picked.

This mutual exclusivity property makes JRadioButtons ideal for options that are inherently exclusive, thus avoiding conflicting selections.

BorderLayout component order

The BorderLayout in Swing organizes components in five specific regions: NORTH, SOUTH, EAST, WEST, and CENTER.
Understanding the order matters because if two components are added to the same region sequentially, only the last one persists.
Here’s how to manage this:

• Each region can hold only one component, so plan your layout with this limitation in mind.
• Try structuring components knowing that any new addition to a filled region will overwrite the previous one.
• If you need multiple components in one region, consider nesting other containers with different layout managers.

Such constraints mean it’s essential to methodically think through where each component should go, ensuring the desired layout is achieved.

JList and scrollbars

By default, a JList doesn’t automatically show scrollbars if items exceed the display area.
To enable scrolling, you should enclose the JList in a JScrollPane.
This process works like this:

• Create your JList with the items you want to display.
• Instantiate a JScrollPane using this JList as a parameter.
• Place the JScrollPane into your container.

This embedding strategy provides your users with a seamless experience where all list items are accessible, even when they go beyond viewable bounds.

MouseMotionListener mouseDragged method

The mouseDragged method is an integral part of handling mouse events in Java Swing, specifically via the MouseMotionListener interface.
It responds to the action of dragging the mouse with a button pressed, which is crucial for interactive applications.
Here’s how to implement and utilize it:

• Implement the MouseMotionListener interface in your class.
• Override the mouseDragged method to perform actions when a drag is detected.
• Attach your MouseMotionListener to the component you want to track for dragging actions, such as a JScrollPane or custom drawing area.

Using mouseDragged enables dynamic UI interactions, like moving graphical components or actively updating interfaces based on user actions.