25+ Free Resources To Learn Java Programming Language Online

Videos, cheat sheets, ebooks, websites, this ultimate resource list have everything that you want to learn about Java! 

Want to learn Java programming for free? Well, you have come to the perfect place. We bring to you 28 free and high quality java learning resources that includes e-books, websites, cheat-sheets and video channels to learn the Java online for free. So make your pick and get started!

e-Books

Official Java EE Tutorial: Official Java Tutorial from Oracle In PDF Format

Official Java Tutorial by Oracle (Sun): This is the official online Java tutorial of book from Addison-Wesley

Think Java: An introduction to java programming for beginners.

Introduction to Programming Using JavaOnline version of book "Introduction to Programming Using Java".

OSGI In Practice: Free PDF Book on Java OSGI Platform development for advanced/expert developers.

Core Servlets and JavaServer: ITs Free Online Version of Core Servlets and JavaServer Pages book

Java Application Development on Linux by Carl Albing and Michael Schwarz: A handy guide for Java development on Linux platform.

Inside the Java Virtual Machine: Free chapters of the a really good book "Inside the Java Virtual Machine" by Bill Venners.

Data Structures and Algorithms with Object-Oriented Design Patterns in Java: A good online book for mid level experienced Java developer to understand design pattern using Java language.

Thinking In Java: Online free Version of popular book Thinking In Java by Bruce Eckel.

Free Websites To Learn Java

Java SE Specification: This contains the Java Language and Virtual Machine Specifications for deeper understanding for Java language.

Java Lessons: Java and JSP Tutorials with Examples.

Java Generics FAQs: A really good question answer format online tutorial for common Java Generics related concepts.

Java Programming FAQs and Tutorials: This site contains many specialized and general Java Programming Topics in question answer format.

Cafeaulait: Single web page tutorial on Java by Elliotte Rusty Harold

Core Servlets Java Tutorials: A very good resource for experienced java developers.

Java Practices: This site provides presentations of Java practices, tasks, and designs, and a huge set of syntax-highlighted code examples.

Programming Notes: Simple java tutorials for beginners.

Top Cheat Sheets For Java

Java API DocsThe best cheat sheet, that I always prefer is Java official API documentation. It handy to easily browse through various classes and their documentation.

Cheatsheet by Princeton University: Summary of most commonly-used Java language features in one page.

Cheatsheet by mindprod.comOne page simple online handy cheat sheet.

DZone Cheatsheets: Best Resource for Java and related technology cheat sheets and good articles.

Quick Reference By Digilife: Contains simple quick notes to use variety of java programming constructs.

Java Reference (By Dream In Code):A simple cheat sheet for java beginners.

Free Video Tutorials

Tutorials for Java Development with Eclipse

Video Tutorials By Java9s

Java Tutorial for Beginners

Java Videos and Screencasts

20 Things Every Java Developer Must Know!

The term 'java developer' covers a wide range of individuals. It starts with fresh graduates looking for jobs and goes up till experienced Java Enterprise Edition developers. There are a wide range of concepts and skills that Java developers must posses in order to be important in the industry. It is highly advisable to know the language fundamentals thoroughly, rather than specific frameworks or syntax.

College Graduates:

A college graduate with no job experience is a fresh mind waiting to become a true Java developer. There are certain things 

that you need to understand as a fresher in the industry to get your dream job.

1. College graduates must know how a Java Virtual Machine works for starters. Concepts like Platform Independence, Garbage 

Collection, class files etc must be clearly understood.

2. They must be aware of the many Object Oriented Programming Concepts implemented in Java.

3. They must know what is multi-threading.

4. Basic understanding of data types and java.lang classes such as String, Math, System etc. is advisable.

5. They must understand the concept of Swing/AWT event based programming.

6. Knowledge of Java Collection framework.

7. They must be clear in the concepts of servlets and JSP.

Java Developers:

You may be a professional Java developer, but that doesn’t firmly guarantee you a job.

1. You must understand design patterns and its usage in Java.

2. You must understand improvements on language from major version changes such as Generics, Annotations, Enums etc.

3. Must know coding conventions.

4. Understand the concepts of Build tool (Ant) and Project Management Tool (Maven). 

5. Understand version control systems, for instance CVS, SVN, Perforce, Clearcase etc.

6. You must know about Apache common libraries among other open source libraries.

7. Understand Unit testing and Continuous Integration Tools.

8. Highly advisable to have fundamental understanding of XML.

9. You must also understand business layer frameworks like Spring. 

Java Enterprise Edition Developers:

Ok, so you are an experienced professional working on Web based development as a JEE developer. Does that mean you can't learn anything?

1. You must have a thorough understanding of MVC frameworks like Struts, Webwork, Tapestry and Spring MVC.

2. You are required to have a fundamental understanding of Web Services. 

3. A thorough understanding of Web or Application servers like Tomcat, Glassfish, WebLogic, WebSphere, Jetty etc is essential.

4. You are required to have a working knowledge of Unix since most Java servers are hosted on Unix-based environment.

Syntax Differences Between C++ And Java

Syntactical differences between Java and C++ are small, but important. It can become difficult for a coder, especially when they are moving from C++ to Java.

Are you having a tough time differentiating between C++ and Java? Do you keep using the semicolon when you're not supposed to? While the two languages are similar, there are certain syntactical differences that can be confusing. Here’s something that will come in handy. The main function C++ int main( int X, char* Y[]) { printf( "Hello, world" ); } Java Every function in Java has to be made a part of a class. So, the main function also has to be a part of a class. Moreover, in Java there is one main() function for every class. This can come in handy when writing unit tests for the class. class HelloWorld { public static void main(String X[]) { System.out.println( "Hello, World" ); } } Compiling C++ In C++, you will be compiling as, g++ X.cc -o outfile This will then be run with, ./outfile Java In Java, you will compile the classes in X.java. javac X.java You have to run this by invoking the static main method. Class declarations While C++ requires a semicolon at the end of class declarations, Java does not have any such requirement. C++ class X{}; Java class X{} Method declarations A method declaration in Java must be a part of a class always. Otherwise, both the languages are quite the same syntactically on this front. You can also use the public, private and protected access specifications in Java. Constructors and destructors In the case of constructors, the syntax in both C++ and Java is the same. Java though has no exact replacement for destructors. Static members Static members (variables and functions) are also declared in the same way in both the languages. But, Java allows for static initialisation blocks in order to initialise static variables. class Foo { static private int x; // static initialization block { x = 5; } } Scoop static namespaces and methods C++ In C++, you will use the Class::method form in order to scoop static methods. class MyClass { public: static do(); }; Use this by, MyClass::do(); Java In Java, on the other hand, scooping comes with the use of the .again parameter. This is similar to accessing the fields of a class. class MyClass { public static do() { // do something } } To use the static method. MyClass.doStuff(); Object declarations C++ // on the stack myClass x; // or on the heap myClass *x = new myClass; Accessing fields from various objects C++ In order to access fields from classes and other such objects, the programmer has to use dots. myClass x; x.field; If a pointed is involved, then the narrow operator (->) has to be used. myClass x = new MyClass(); x->field; Java In Java, only the dot is used. Since we always use references in Java, even pointers are accessed using the dot. myClass x = new MyClass(); x.field; Protection levels They are specified in a different manner. C++ public: void X(); void Y(); Java public void X(); public void Y(); Virtual functions C++ virtual int X(); Virtual functions can also be used non virtually. You can simply say into X(). Java int foo(); // or, final int foo(); In Java, functions are always virtual by default. You use ‘final’ in order to avoid them from being overridden. Abstract Classes C++ All you need to do is include public virtual functions./ class X{ public: virtual void X() = 0; }; Java In Java the syntax allows the programmer to be explicit. abstract class X{ public abstract void X(); } If you want to specify an interface, then say, interface X{ public void foo(); } In that case though, you will have to implement it by, class Y implements X { public void M() { /* do something */ } } Memory management This is also pretty much the same in both the languages, except that Java has garbage collection, so no delete for Java.

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20 Things That Java Developers Must Concentrate On!

The term 'java developer' covers a wide range of candidates. It starts with fresh graduates looking for jobs and goes up till experienced Java Enterprise Edition developers. The language has also evolved and grown over the past decade or so. It has gained importance in various platforms. As a result, there are a wide range of concepts and skills that Java developers must posses in order to be important in the industry.

College Graduates: A college graduate is a fresh mind waiting to become a true Java developer. There are certain things that you need to understand as a fresher in the industry to find a job.

1. How the JVM works: You have to understand things like garbage collection, platform independence and class files.

2. OOP Concepts In Java

3. Multi-threading

4. Java Collection framework

5. Understanding data types and java.lang classes: Classes like Math, String, System and others are very important if you want to become a Java developer.

6. Event based programming using Swing and AWT concepts.

7. Servlets & JSP concepts

Java Developers: You may be a professional Java developer, but that doesn’t mean that a job is guaranteed. It is not easy by any means, in fact, Java developers face tough competition in the job market. Here are some of the skills that you must have.

1. Design patterns and their usage 

2. Improvements in Java as part of major changes in the language: These include things like Annotations, Enums, Generics etc.

3. Coding Conventions 

4. Build tools and Project Management Tools: Ant is a build tool and Maven is a project management tool. You must understand this.

5. Version control System like CVS/SVN/Perforce/Clearcase

6. Open source libraries: The Apache Commons Libraries comes to mind.

7. Unit testing and Continuous Integration Tools

8. XML fundamentals

9. Business layers frameworks like Spring

Java Enterprise Edition Developers

For those working with JEE, there are certain additional concepts that they need to understand.

1. MVC Frameworks: These include Struts, Webwork, Tapestry and Spring MVC.

2. Web Application Servers: This includes servers like WebLogic, Glassfish, Tomcat, Jetty, WebSphere and others.

3. Unix environment: Most Java servers are hosted on Unix based environments, so a JEE developer must understand the same. Even if you don’t have in depth knowledge, you need to know the basics of an Unix-based environment.