Advanced Java Tutorial

Advanced Java Tutorial

Last updated on 12th Oct 2020, Blog, Tutorials

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Java is a high-level programming language originally developed by Sun Microsystems and released in 1995. Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX. This tutorial gives a complete understanding of Java. This reference will take you through simple and practical approaches while learning Java Programming language.

Why to Learn java Programming?

Java is a MUST for students and working professionals to become a great Software Engineer specially when they are working in Software Development Domain. I will list down some of the key advantages of learning Java Programming:

1. Object Oriented − In Java, everything is an Object. Java can be easily extended since it is based on the Object model.

2. Platform Independent − Unlike many other programming languages including C and C++, when Java is compiled, it is not compiled into platform specific machine, rather into platform independent byte code. This byte code is distributed over the web and interpreted by the Virtual Machine (JVM) on whichever platform it is being run on.

3. Simple − Java is designed to be easy to learn. If you understand the basic concept of OOP Java, it would be easy to master.

4. Secure − With Java’s secure feature it enables to develop virus-free, tamper-free systems. Authentication techniques are based on public-key encryption.

5. Architecture-neutral − Java compiler generates an architecture-neutral object file format, which makes the compiled code executable on many processors, with the presence of Java runtime system.

6. Portable − Being architecture-neutral and having no implementation dependent aspects of the specification makes Java portable. Compiler in Java is written in ANSI C with a clean portability boundary, which is a POSIX subset.

7. Robust − Java makes an effort to eliminate error prone situations by emphasizing mainly on compile time error checking and runtime checking.

Hello World using Java Programming.

Just to give you a little excitement about Java programming, I’m going to give you a small conventional C Programming Hello World program, You can try it using Demo link.

Live Demo

  • public class MyFirstJavaProgram {
  •    /* This is my first java program.
  •     * This will print ‘Hello World’ as the output
  •     */
  •    public static void main(String []args) {
  •       System.out.println(“Hello World”); // prints Hello World
  •    }
  • }

Applications of Java Programming

The latest release of the Java Standard Edition is Java SE 8. With the advancement of Java and its widespread popularity, multiple configurations were built to suit various types of platforms. For example: J2EE for Enterprise Applications, J2ME for Mobile Applications.

The new J2 versions were renamed as Java SE, Java EE, and Java ME respectively. Java is guaranteed to be Write Once, Run Anywhere.

1. Multithreaded − With Java’s multithreaded feature it is possible to write programs that can perform many tasks simultaneously. This design feature allows the developers to construct interactive applications that can run smoothly.

2. Interpreted − Java byte code is translated on the fly to native machine instructions and is not stored anywhere. The development process is more rapid and analytical since the linking is an incremental and light-weight process.

3. High Performance − With the use of Just-In-Time compilers, Java enables high performance.

4. Distributed − Java is designed for the distributed environment of the internet.

5. Dynamic − Java is considered to be more dynamic than C or C++ since it is designed to adapt to an evolving environment. Java programs can carry extensive amount of run-time information that can be used to verify and resolve accesses to objects on run-time.

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Audience

This tutorial has been prepared for the beginners to help them understand the basic to advanced concepts related to Java Programming language.

Prerequisites

Before you start practicing various types of examples given in this reference, we assume that you are already aware about computer programs and computer programming languages.

Java programming language was originally developed by Sun Microsystems which was initiated by James Gosling and released in 1995 as core component of Sun Microsystems’ Java platform (Java 1.0 [J2SE]).

The latest release of the Java Standard Edition is Java SE 8. With the advancement of Java and its widespread popularity, multiple configurations were built to suit various types of platforms. For example: J2EE for Enterprise Applications, J2ME for Mobile Applications.

The new J2 versions were renamed as Java SE, Java EE, and Java ME respectively. Java is guaranteed to be Write Once, Run Anywhere.

History of Java

James Gosling initiated Java language project in June 1991 for use in one of his many set-top box projects. The language, initially called ‘Oak’ after an oak tree that stood outside Gosling’s office, also went by the name ‘Green’ and ended up later being renamed as Java, from a list of random words.

Sun released the first public implementation as Java 1.0 in 1995. It promised Write Once, Run Anywhere (WORA), providing no-cost run-times on popular platforms.

On 13 November, 2006, Sun released much of Java as free and open source software under the terms of the GNU General Public License (GPL).

On 8 May, 2007, Sun finished the process, making all of Java’s core code free and open-source, aside from a small portion of code to which Sun did not hold the copyright.

Tools You Will Need

For performing the examples discussed in this tutorial, you will need a Pentium 200-MHz computer with a minimum of 64 MB of RAM (128 MB of RAM recommended).

You will also need the following softwares −

  • Linux 7.1 or Windows xp/7/8 operating system
  • Java JDK 8
  • Microsoft Notepad or any other text editor

This tutorial will provide the necessary skills to create GUI, networking, and web applications using Java.

What is Next?

The next chapter will guide you to how you can obtain Java and its documentation. Finally, it instructs you on how to install Java and prepare an environment to develop Java applications.

In this chapter, we will discuss on the different aspects of setting up a congenial environment for Java.

Local Environment Setup

If you are still willing to set up your environment for Java programming language, then this section guides you on how to download and set up Java on your machine. Following are the steps to set up the environment.

Java SE is freely available from the link Download Java. You can download a version based on your operating system.

Follow the instructions to download Java and run the .exe to install Java on your machine. Once you installed Java on your machine, you will need to set environment variables to point to correct installation directories −

Setting Up the Path for Windows

Assuming you have installed Java in c:\Program Files\java\jdk directory −

  • Right-click on ‘My Computer’ and select ‘Properties’.
  • Click the ‘Environment variables’ button under the ‘Advanced’ tab.
  • Now, alter the ‘Path’ variable so that it also contains the path to the Java executable. Example, if the path is currently set to ‘C:\WINDOWS\SYSTEM32’, then change your path to read ‘C:\WINDOWS\SYSTEM32;c:\Program Files\java\jdk\bin’.

Setting Up the Path for Linux, UNIX, Solaris, FreeBSD

Environment variable PATH should be set to point to where the Java binaries have been installed. Refer to your shell documentation, if you have trouble doing this.

Example, if you use bash as your shell, then you would add the following line to the end of your ‘.bashrc: export PATH = /path/to/java:$PATH’

Popular Java Editors

To write your Java programs, you will need a text editor. There are even more sophisticated IDEs available in the market. But for now, you can consider one of the following −

  • Notepad − On Windows machine, you can use any simple text editor like Notepad (Recommended for this tutorial), TextPad.
  • Netbeans − A Java IDE that is open-source and free which can be downloaded from https://www.netbeans.org/index.html.
  • Eclipse − A Java IDE developed by the eclipse open-source community and can be downloaded from https://www.eclipse.org/.

What is Next?

Next chapter will teach you how to write and run your first Java program and some of the important basic syntaxes in Java needed for developing applications.

When we consider a Java program, it can be defined as a collection of objects that communicate via invoking each other’s methods. Let us now briefly look into what do class, object, methods, and instance variables mean.

  • 1. Object − Objects have states and behaviors. Example: A dog has states – color, name, breed as well as behavior such as wagging their tail, barking, eating. An object is an instance of a class.
  • 2. Class − A class can be defined as a template/blueprint that describes the behavior/state that the object of its type supports.
  • 3. Methods − A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.
  • 4. Instance Variables − Each object has its unique set of instance variables. An object’s state is created by the values assigned to these instance variables.

First Java Program

Let us look at a simple code that will print the words Hello World.

Example

  • public class MyFirstJavaProgram {
  •    /* This is my first java program.
  •     * This will print ‘Hello World’ as the output
  •     */
  •    public static void main(String []args) {
  •       System.out.println(“Hello World”); // prints Hello World
  •    }
  • }

Let’s look at how to save the file, compile, and run the program. Please follow the subsequent steps −

  1. 1. Open notepad and add the code as above.
  2. 2. Save the file as: MyFirstJavaProgram.java.
  3. 3. Open a command prompt window and go to the directory where you saved the class. Assume it’s C:\.
  4. 4. Type ‘javac MyFirstJavaProgram.java’ and press enter to compile your code. If there are no errors in your code, the command prompt will take you to the next line (Assumption : The path variable is set).
  5. 5. Now, type ‘ java MyFirstJavaProgram ‘ to run your program.
  6. 6. You will be able to see ‘ Hello World ‘ printed on the window.
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Output

C:\> javac MyFirstJavaProgram.java

C:\> java MyFirstJavaProgram 

Hello World

Basic Syntax

About Java programs, it is very important to keep in mind the following points.

  • Case Sensitivity − Java is case sensitive, which means identifier Hello and hello would have different meaning in Java.
  • Class Names − For all class names the first letter should be in Upper Case. If several words are used to form a name of the class, each inner word’s first letter should be in Upper Case.

Example:
  • class MyFirstJavaClass
  • Method Names − All method names should start with a Lower Case letter. If several words are used to form the name of the method, then each inner word’s first letter should be in Upper Case.

Example:
  • public void myMethodName()
  • Program File Name − Name of the program file should exactly match the class name.
    When saving the file, you should save it using the class name (Remember Java is case sensitive) and append ‘.java’ to the end of the name (if the file name and the class name do not match, your program will not compile).
    But please make a note that in case you do not have a public class present in the file then file name can be different than class name. It is also not mandatory to have a public class in the file.
    Example: Assume ‘MyFirstJavaProgram’ is the class name. Then the file should be saved as ‘MyFirstJavaProgram.java’
  • public static void main(String args[]) − Java program processing starts from the main() method which is a mandatory part of every Java program.

Java Identifiers

All Java components require names. Names used for classes, variables, and methods are called identifiers.

In Java, there are several points to remember about identifiers. They are as follows −

  • All identifiers should begin with a letter (A to Z or a to z), currency character ($) or an underscore (_).
  • After the first character, identifiers can have any combination of characters.
  • A key word cannot be used as an identifier.
  • Most importantly, identifiers are case sensitive.
  • Examples of legal identifiers: age, $salary, _value, __1_value.
  • Examples of illegal identifiers: 123abc, -salary.

Java Modifiers

Like other languages, it is possible to modify classes, methods, etc., by using modifiers. There are two categories of modifiers −

  1. 1. Access Modifiers − default, public , protected, private
  2. 2. Non-access Modifiers − final, abstract, strictfp

We will be looking into more details about modifiers in the next section.

Java Variables

Following are the types of variables in Java −

  • Local Variables
  • Class Variables (Static Variables)
  • Instance Variables (Non-static Variables)

Java Arrays

Arrays are objects that store multiple variables of the same type. However, an array itself is an object on the heap. We will look into how to declare, construct, and initialize in the upcoming chapters.

Java Enums

Enums were introduced in Java 5.0. Enums restrict a variable to have one of only a few predefined values. The values in this enumerated list are called enums.

With the use of enums it is possible to reduce the number of bugs in your code.

For example, if we consider an application for a fresh juice shop, it would be possible to restrict the glass size to small, medium, and large. This would make sure that it would not allow anyone to order any size other than small, medium, or large.

Example:

  • class FreshJuice {
  •    enum FreshJuiceSize{ SMALL, MEDIUM, LARGE }
  •    FreshJuiceSize size;
  • }
  • public class FreshJuiceTest {
  •    public static void main(String args[]) {
  •       FreshJuice juice = new FreshJuice();
  •       juice.size = FreshJuice.FreshJuiceSize.MEDIUM ;
  •       System.out.println(“Size: ” + juice.size);
  •    }
  • }

The above example will produce the following result −

Output

Size: MEDIUM

Note − Enums can be declared as their own or inside a class. Methods, variables, constructors can be defined inside enums as well.

Java Keywords

The following list shows the reserved words in Java. These reserved words may not be used as constant or variable or any other identifier names.

abstractassertbooleanbreak
bytecasecatchchar
classconstcontinuedefault
dodoubleelseenum
extendsfinalfinallyfloat
forgotoifimplements
importinstanceofintinterface
longnativenewpackage
privateprotectedpublicreturn
shortstaticstrictfpsuper
switchsynchronizedthisthrow
throwstransienttryvoid
volatilewhile

Comments in Java

Java supports single-line and multi-line comments very similar to C and C++. All characters available inside any comment are ignored by Java compiler.

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Example

  • public class MyFirstJavaProgram {
  •    /* This is my first java program.
  •     * This will print ‘Hello World’ as the output
  •     * This is an example of multi-line comments.
  •     */
  •    public static void main(String []args) {
  •       // This is an example of single line comment
  •       /* This is also an example of single line comment. */
  •       System.out.println(“Hello World”);
  •    }
  • }

Output

Hello World

Using Blank Lines

A line containing only white space, possibly with a comment, is known as a blank line, and Java totally ignores it.

Inheritance

In Java, classes can be derived from classes. Basically, if you need to create a new class and here is already a class that has some of the code you require, then it is possible to derive your new class from the already existing code.

This concept allows you to reuse the fields and methods of the existing class without having to rewrite the code in a new class. In this scenario, the existing class is called the superclass and the derived class is called the subclass.

Interfaces

In Java language, an interface can be defined as a contract between objects on how to communicate with each other. Interfaces play a vital role when it comes to the concept of inheritance.

An interface defines the methods, a deriving class (subclass) should use. But the implementation of the methods is totally up to the subclass.

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