Java Garbage Collection and Memory Management
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Questions and Answers

What is the purpose of the BorderLayout() method?

Constructs a new border layout with no gaps between the components.

How does the GridLayout(int rows, int columns) method work?

Creates a grid layout with the specified number of rows and columns.

What happens when both the number of rows and the number of columns are set to non-zero values in the GridLayout method?

The number of columns specified is ignored, and the number of columns is determined from the specified number of rows and the total number of components in the layout.

What is the purpose of the hgap and vgap parameters in the BorderLayout(int hgap, int vgap) method?

<p>They specify the gaps between the components.</p> Signup and view all the answers

What is the default behavior of the GridLayout() method?

<p>It creates a grid layout with one column per component, in a single row.</p> Signup and view all the answers

What happens when you specify a value of zero for the rows or columns in the GridLayout method?

<p>It means that the number of rows or columns will be determined as needed.</p> Signup and view all the answers

How does the BorderLayout arrange components?

<p>It arranges components in five regions: north, south, east, west, and center.</p> Signup and view all the answers

What is the purpose of the GridLayout(int rows, int cols, int hgap, int vgap) method?

<p>It creates a grid layout with the specified number of rows and columns, and with the specified gaps between components.</p> Signup and view all the answers

What is the effect of setting rows and cols to zero in the GridLayout method?

<p>It is not allowed, as rows and cols cannot both be zero.</p> Signup and view all the answers

What happens to the number of columns in a GridLayout when the number of rows is specified?

<p>The number of columns is determined from the specified number of rows and the total number of components in the layout.</p> Signup and view all the answers

Study Notes

Java Garbage Collection

  • Java programs perform automatic memory management through Java Garbage Collection
  • Java programs run on a Java Virtual Machine (JVM), where objects are created on the heap, a portion of memory dedicated to the program
  • The heap memory consists of two types of objects: live (being used and referenced) and dead (no longer used or referenced)
  • The garbage collector finds unused objects and deletes them to free up memory

Destructor

  • A destructor is called to release resources, such as releasing locks, closing database connections or files, releasing network resources, and recovering heap space allocated during an object's lifetime
  • The Java finalize() method is used to provide immediate access to memory management and works similarly to a destructor

Object Reference Release

  • References to an object can be released to make it a candidate for garbage collection by:
    • Making a reference null
    • Assigning a reference to another
    • Using an anonymous object

Inheritance

  • Inheritance is used to avoid repetition in implementations
  • The classes in the awt and swing packages can be classified into two broad categories: GUI classes and Non-GUI classes

AWT

  • Abstract Windowing Toolkit (AWT) contains original GUI components that came with the first release of JDK
  • AWT components are operating system dependent and rely on the local platform's windowing system
  • AWT components are often called heavy weight components (HWC) and have a non-configurable appearance

Swing

  • Swing components are the newest GUI components built on top of AWT
  • Swing components are called pure Java components, written, manipulated, and displayed completely in Java
  • Swing is independent of the operating system and has a rich set of classes (e.g., JPanel, JButton, JTextArea)
  • Most Swing components are light weight components (LWC)

Swing Architecture

  • Swing components follow a Model-View-Controller (MVC) architecture
    • Model represents a component's data
    • View represents the visual representation of a component's data
    • Controller takes input from the user and reflects changes in the component's data

Swing Components

  • Top-level containers: JFrame, JDialog, JApplet
  • Components: JButton, JTextField, JLabel, JTextArea, JPasswordField, ImageIcon, JScrollbar, JProgressBar
  • Containers: JPanel, JBox

Swing Inheritance Hierarchy

  • Component (AWT) -> Window -> Frame -> JFrame (Swing)
  • Component (AWT) -> Container -> JComponent (Swing) -> various Swing components (e.g., JButton, JLabel, JTextArea)

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Description

Learn about Java garbage collection, a process that automatically manages memory in Java programs. Understand how Java programs run on the JVM and how objects are created on the heap.

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