Java Introduction

Introduction to Java

What is Java?

Java is a popular, high-level, class-based, and object-oriented programming language. It was originally developed by James Gosling at Sun Microsystems and released in 1995. Today, it is owned and maintained by Oracle Corporation.

Java was designed to have as few implementation dependencies as possible. It is a general-purpose programming language intended to let application developers "write once, run anywhere" (WORA), meaning that compiled Java code can run on all platforms that support Java without the need for recompilation.

Why Learn Java?

Java continues to be one of the most popular programming languages in the world for several reasons:

1. Platform Independent: Java works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc.). You don't need to write different code for different operating systems.
2. Huge Demand: It is one of the most popular enterprise programming languages and has massive job market demand. Many Fortune 500 companies rely on Java for their backend systems.
3. Object-Oriented: Java allows you to create modular programs and highly reusable code, making complex software easier to manage and scale.
4. Large Community: It features a massive ecosystem of libraries, frameworks (like Spring, Hibernate), and unparalleled developer support on forums like StackOverflow.
5. Secure: Java has built-in security features, such as the bytecode verifier, the classloader, and a security manager that sandboxes untrusted code.
6. Multithreaded: Java has native support for multithreading, which allows you to write programs that can perform multiple tasks simultaneously, maximizing CPU utilization.

A Brief History of Java

The history of Java is quite fascinating. The project was initiated by James Gosling, Mike Sheridan, and Patrick Naughton in June 1991. The small team of sun engineers was called the Green Team.

Initially, it was designed for interactive television, but it was too advanced for the digital cable television industry at the time.

• 1991: The language was initially called Oak after an oak tree that stood outside Gosling's office.
• 1995: It was renamed to Java, inspired by Java coffee, an espresso bean. The first public implementation was released as Java 1.0. It promised "Write Once, Run Anywhere" (WORA) functionality, providing no-cost run-times on popular platforms.
• 2006: Sun Microsystems released much of its Java virtual machine (JVM) as free and open-source software.
• 2010: Oracle Corporation acquired Sun Microsystems and took over the stewardship of Java.

Today, Java undergoes a rapid release cadence, with a new version released every six months (in March and September) to keep up with modern programming trends.

Core Components of Java

To understand how Java works, you need to understand its three core components:

1. JDK (Java Development Kit)

The JDK is a software development environment used to develop Java applications and applets. It physically exists. It contains the JRE + development tools (like the compiler javac, an archiver jar, a documentation generator javadoc, etc.). If you want to write Java programs, you must install the JDK.

2. JRE (Java Runtime Environment)

The JRE provides the libraries, the Java Virtual Machine (JVM), and other components to run applets and applications written in the Java programming language. It physically exists. It does not contain any development tools like a compiler or debugger. If you only want to run Java programs (not write them), you only need the JRE.

3. JVM (Java Virtual Machine)

The JVM is an abstract machine. It is a specification that provides a runtime environment in which Java bytecode can be executed. JVMs are available for many hardware and software platforms. The JVM performs the following main tasks:

• Loads the code
• Verifies the code
• Executes the code
• Provides runtime environment

How Java Works Internally

When you write a Java program, the execution process goes through several distinct phases:

1. Source Code: You write your code in a text editor or IDE and save it with a .java extension (e.g., Main.java).
2. Compilation: You use the Java Compiler (javac) to compile this source code. Unlike C++ which compiles down to machine code, the Java compiler converts your source code into Bytecode (saved as a .class file). Bytecode is a highly optimized set of instructions.
3. Classloader: When you run the program, the JVM's Classloader subsystem loads the .class files into memory.
4. Bytecode Verifier: The JVM checks the bytecode for security breaches and illegal code that could violate access rights.
5. Execution: Finally, the Execution Engine runs the bytecode. It uses a combination of an Interpreter (which reads bytecode line by line) and a JIT (Just-In-Time) Compiler (which compiles frequently used bytecode down to native machine code for faster execution).

This multi-step process is what gives Java its platform independence and its robust security model.

Features of Java

Java's creators outlined several key principles that guided the language's design. These are often referred to as the "Java Buzzwords":

• Simple: Java is designed to be easy to learn. If you understand the basic concept of OOP Java, it would be easy to master. It removed many complex features of C++ like explicit pointers and operator overloading.
• Object-Oriented: In Java, everything is an Object. Java can be easily extended since it is based on the Object model.
• Robust: Java makes an effort to eliminate error-prone situations by emphasizing mainly on compile-time error checking and runtime checking. It features strong memory management and automatic garbage collection.
• Architecture-neutral: The compiler generates an architecture-neutral object file format, which makes the compiled code executable on many processors, given the presence of the Java runtime system.
• Portable: Being architecture-neutral and having no implementation dependent aspects of the specification makes Java portable. The compiler in Java is written in ANSI C with a clean portability boundary, which is a POSIX subset.
• High Performance: With the use of Just-In-Time (JIT) compilers, Java enables high performance.
• Distributed: Java is designed for the distributed environment of the internet.
• 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.

Applications of Java

Because of its versatility and robustness, Java is used in a wide variety of domains:

1. Enterprise Applications: Java is the backbone of many large-scale banking, financial, and enterprise systems. The Spring framework is highly dominant in this area.
2. Android App Development: For a long time, Java was the primary language for Android development (before Kotlin became the preferred choice, though Java is still heavily used and supported).
3. Web Applications: Java provides technologies like Servlets, Struts, Spring Boot, and JSPs for creating dynamic web applications.
4. Big Data Technologies: Hadoop and other big data frameworks are written in or heavily support Java.
5. Cloud-Based Applications: Java is widely used for creating cloud-native applications and microservices.
6. Scientific Applications: Java is a choice for scientific applications due to its safety, portability, and strong concurrency tools.
7. Embedded Systems: Originally designed for embedded systems, Java is still used in smart cards, sensors, and IoT devices.

Java Ecosystem and Tooling

When you enter the Java world, you don't just get a language; you get a massive, mature ecosystem. Some of the most important tools include:

• Build Tools: Apache Maven and Gradle are used to manage project dependencies and automate the build process.
• IDEs: IntelliJ IDEA, Eclipse, and Apache NetBeans are powerful Integrated Development Environments that provide intelligent code completion, refactoring, and debugging.
• Frameworks: Spring Boot (for standalone, production-grade Spring based Applications), Hibernate (for database ORM), and Java EE (Enterprise Edition) are industry standards.
• Testing: JUnit and TestNG are the dominant frameworks for writing unit tests.

Java vs. C++

If you're coming from a C++ background, you'll notice several differences:

• Java does not support pointers directly to avoid memory access errors.
• Java uses automatic garbage collection; C++ requires manual memory management (new and delete).
• Java does not support multiple inheritance for classes (it uses Interfaces instead) to avoid the "Diamond Problem".
• Java is strictly object-oriented (you cannot write a function outside of a class), whereas C++ is a multi-paradigm language.

What's Next?

In the next chapter, we will guide you through setting up your environment (if you choose to install it locally) and writing your very first Java program. However, remember that you can test all the code examples directly here on IntricateDevo using our interactive "Try it Yourself" editor!