It's all about Java

First of all, please read below blog post to understand basics of Exception Handling in java. Exception handling and java keywords To continue from there, Basically Java default API has hierarchy of  java classes to support different uses cases of exceptions.  The parent class of all Exceptions and Errors is Throwable . Please check below pictorial representation of  API Hierarchy. Exception: The class Exception and any subclasses that are also not subclasses of RuntimeException are checked exceptions. And all subclasses of RuntimeException and RuntimeException class itself are Unchecked exception . Rest all are Checked exceptions Examples of Unchecked Exceptions:            ArrayIndexOutOfBoundException          NullPointerException Error: An Error is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch. Most such errors are abnormal conditions. Examples: T...

Java is an object oriented programming language which can be downloaded and installed in your local Machine from java.com To explain java binaries and tools requires block diagram which gives clear picture. For now I brief few important tools. JDK - java development toolkit JVM - Java virtual machine JRE - Java Run time environment From oracle site we can download JDK which is shipped along with JVM and JRM. Mostly java programmers need the JDK. For end users JRE alone is enough. Basic OOPS characteristics are Inheritance Encapsulation Abstraction and Polymorphism The above concepts collectively makes application software extendable and changeable with less effort. Also helps in Developing design patterns. Design patterns gives solutions for common challenges usually a programmer faces while development applications. Factory design pattern, Abstract design pattern, Builder pattern etc. I explain these Design patterns in another article. Inheritance : Inherita...

This article is continuation of previous post JFrame usage demo . Please read it before continuing. This post uses the same example code shown in  JFrame usage demo  with JLabel changes and introduces layout manager BorderLayout. Layout Manager: Layout manager is responsible to arrange components on containers. Usually every swing container is created with a default layout manager but can be changed with setLayout() api. For example JFrame uses BorderLayout as default layout amanger. Java program for JLabel 1  2   import java.awt.BorderLayout; 3   import java.awt.Color; 4   import java.awt.Font; 5  6   import javax.swing.JFrame; 7   import javax.swing.JLabel; 8   import javax.swing.SwingUtilities; 9  10  /** 11   * 12   * Simple class to demonstrate JLabel of swing toolkit 13   * 14   * @author Nagasharath 15   * 16  ...

Java Multi threaded programming basics with Reentrant locks As we have seen in earlier post that implicit locking mechanism achieved using synchronized keyword slows down the application performance. Hence java concurrency api gives explicit locking mechanism to achieve mutual exclusion among shared object. How using explicit locks are better than implicit lock? Explicit lock acquires lock per Thread basis and not per method invoke basis. It is inverse in the case of implicit lock.   If a method is synchronized then every invocation of that method involves acquiring and releasing of lock. This process really slows down the application performance.  Hence it is always good idea to prefer reentrent lock or explicit lock to implicit lock. ReentrantLock is a class available in java.util.concurrency package lock() and unlock() methods are used used to acquire and release the lock. Condition class is used in place of Object class wait(), notifyAll() and notify(). ...

Graphical user interface in short GUI makes computer users easy to understand and use the application software comfortably. Almost all modern programming languages allows application developers to develop GUIs. Java has AWT/Swing as default API as part of Java Foundation classes in short JFC which are shipped with JDK. Hence these toolkits can be used directly in our applications with out adding external libraries like jars to our application's class path. But there are some other toolkits which found useful and industry endorsed in developing GUI.      SWT       JFaces [Framework for SWT]      Java FX      Swing      AWT AWT: Abstract window toolkit is available since java first version. AWT uses native operating system resources like Fonts, colors and components like table, tree, dialogues, windows etc. Few notable points about AWT: AWT is heavy weight. It uses OS resources There are l...

All modern computer hardware architectures and operating systems are capable and optimized for multi processor system and multi threaded system.  Process Vrs Thread: Process is heavy weight where as Thread is light weight. Thread is light weight because process uses it's own address space and thread shares the Process's address space. So Threads are considered to be subset of a process. more over threads consumes less OS resources in terms of physical memory and uses CPU time at most. Junior programmers think concurrency is hard.  Experienced programmers think concurrency is easy.  Senior programmers think concurrency is hard.                                                                                    _ Java Concurrency Essentials by Martin ...

Every Java programmer must read and understand the following books. 1. Effective Java 2. Concurrency in practice Effective Java: This book is authored by Joshua Bloch. He took the major role in authoring the java.util package which is [collection framework] one of the java core libraries. He explains the best practices that every programmer should consider while writing java programs. Some of them are: Contract between hashcode() and equals() of Object class when programmer overrides one of these methods in their classes Exceptions concurrency: Inter thread communication, synchronization etc Immutable Objects The above points are few among others. Concurrency in practice: This book gives complete explanation about how efficient concurrency is achieved in java programs using concurrency utility classes which were introduced in Java 5 version. This book is authored by: Brian Goetz Tim peierls Joshua Bloch Joseph Bowbeer David Holmes and Doug Lea ...

Simple program which demonstrates Swing/AWT Grid layout: This post is intended to the beginners of swing/awt. This below program creates a JFrame with 2 labels, 2 textfields and 2 buttons. import java.awt.GridLayout; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JPasswordField; import javax.swing.JTextField; /**  * @author Nagasharath Kopalle  *  * Simple program to demontrate Gridlayout  *  */ public class GridLayoutDemo extends JFrame { private JLabel labelName = null; private JTextField textFieldName = null; private JLabel labelPassword = null; private JPasswordField passwordFieldPassword = null; private JButton buttonSubmit = null; private JButton buttonCancel = null; /** * */ public GridLayoutDemo() { initComponents(); } /** * instantiates components and adds properties. */ void initComponents() { this.setTitle("Grid Layout Dem...

Eclipse Oxygen Java editor Shortcuts helps in editing source code more comfortably. Frequently used default shortcuts are listed below.  Description Shortcut Delete Line CTRL + D Copy Line CTRL + ALT + Down Arrow Add method level, class level, member level Comments SHIFT + ALT + J Format Java Source code CTRL + SHIFT + F Make line commented CTRL + / Make multiple lines [block] commented   CTRL + SHIFT + / Search selected similar word within the source document CTRL + K Select line from beginning to end SHIFT + End key Select line from end to beginning SHIFT + Home key Select Word by word in same line CTRL + SHIFT + Right Arrow Move line above ALT + Up Arrow Move line below ALT + Down Arrow Shortcuts can ...

1. Since Swing is not thread safe, it is not at all a good practice to launch a UI Container like JFrame, JDialog etc in main Thread. 2. Doing so leads to incorrect behavior of java GUI. 3. To avoid this, Swing toolkit has predefined API as part of JFC. 4.    a. SwingUtilities.invokeAndWait(Runnable r);        b. SwingUtilities.invokeLater(Runnable r); 5. Which part of the code must be in UI Thread?         a. setVisible(true);         b. show(); [deprecated]  and c. pack();       6. Call to these methods mentioned in 5(a), 5(b), and 5(c) must happen in one of the methods mentioned in point 4(a) and point 4(b). That's enough. :)          Example :                        public static void main(String[] args){                         ...

This post is intended to beginners of java swing toolkit programmers. It is a simple java program which demonstrates the swing based File explorer GUI. import java.awt.GridLayout; import java.io.File; import java.lang.reflect.InvocationTargetException; import java.util.Arrays; import java.util.List; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTree; import javax.swing.SwingUtilities; import javax.swing.UIManager; import javax.swing.UnsupportedLookAndFeelException; import javax.swing.event.TreeModelListener; import javax.swing.tree.TreeModel; import javax.swing.tree.TreePath; /**  * @author NagasharathK  *  */ public class FileExplorer extends JFrame { private JTree fileManagerTree = null; public FileExplorer() { initComponents(); } /** * Initializes components */ private void initComponents() { this.getContentPane().add(new JScrollPane(createFileManagerTree(...