1. Introduction to Java

Java is a high-level, general-purpose, object-oriented, and secure programming language developed by James Gosling at Sun Microsystems, Inc. in 1991. It is formally known as OAK. In 1995, Sun Microsystem changed the name to Java. In 2009, Sun Microsystem takeover by Oracle Corporation.

Editions of Java
Each edition of Java has different capabilities. There are three editions of Java:

• Java Standard Editions (JSE): It is used to create programs for a desktop computer.

• Java Enterprise Edition (JEE): It is used to create large programs that run on the server and manages heavy traffic and complex transactions.

• Java Micro Edition (JME): It is used to develop applications for small devices such as set-top boxes, phone, and appliances.

Features of Java

• Simple: Java is a simple language because its syntax is simple, clean, and easy to understand. Complex and ambiguous concepts of C++ are either eliminated or re-implemented in Java. For example, pointer and operator overloading are not used in Java.

• Object-Oriented: In Java, everything is in the form of the object. It means it has some data and behavior. A program must have at least one class and object.

• Robust: Java makes an effort to check error at run time and compile time. It uses a strong memory management system called garbage collector. Exception handling and garbage collection features make it strong.

• Secure: Java is a secure programming language because it has no explicit pointer and programs runs in the virtual machine. Java contains a security manager that defines the access of Java classes.

• Platform-Independent: Java provides a guarantee that code writes once and run anywhere. This byte code is platform-independent and can be run on any machine.

• Portable: Java Byte code can be carried to any platform. No implementation-dependent features. Everything related to storage is predefined, for example, the size of primitive data types.

• High Performance: Java is an interpreted language. Java enables high performance with the use of the Just-In-Time compiler.

• Distributed: Java also has networking facilities. It is designed for the distributed environment of the internet because it supports TCP/IP protocol. It can run over the internet. EJB and RMI are used to create a distributed system.

• Multi-threaded: Java also supports multi-threading. It means to handle more than one job a time.

Differences between C, C++ and Java

Java Runtime Environment (JRE)

Together, the Java Development Kit(JDK), the Java Virtual Machine (JVM), and the Java Runtime Environment (JRE) form a powerful trifecta of Java platform components for developing and running Java applications. I've previously introduced the JDK and JVM.

A runtime environment is a piece of software that is designed to run other software. As the runtime environment for Java, the JRE contains the Java class libraries, the Java class loader, and the Java Virtual Machine. 

 In this system:

• The class loader is responsible for correctly loading classes and connecting them with the core Java class libraries.

• The JVM is responsible for ensuring Java applications have the resources they need to run and perform well in your device or cloud environment.

• The JRE is mainly a container for those other components, and is responsible for orchestrating their activities.
  
  

Java Runtime Environment
 The Java Runtime Environment is a software layer that runs on top of a computer's operating system, providing additional services specific to Java.The JRE smoothes over the diversity of operating systems, ensuring that Java programs can run on virtually any OS without modification. It also provides value-added services. Automatic memory management is one of the JRE's most important services, ensuring that programmers don't have to manually control the allocation and reallocation of memory.

How the JRE works with the JVM
A Java Virtual Machine is a running software system responsible for executing live Java programs. The JRE is the on-disk system that takes your Java code, combines it with the necessary libraries, and starts the JVM to execute it. As an example, the Java class loader is part of the Java Runtime Environment. This important piece of software loads compiled Java code into memory and connects the code to the appropriate Java class libraries.

 

The Java Development Kit (JDK) is a software development environment used for developing Java applications and applets. It includes the Java Runtime Environment (JRE), an interpreter/loader (java), a compiler (javac), an archiver (jar), a documentation generator (javadoc) and other tools needed in Java development.
Java developers are initially presented with two JDK tools, java and javac. Both are run from the command prompt. Java source files are simple text files saved with an extension of .java. After writing and saving Java source code, the javac compiler is invoked to create .class files. Once the .class files are created, the 'java' command can be used to run the java program.
Introduction to API in Java.
 

Java Development Kit (JDK) 

An API can be described as a way to enable computers to possess a common interface, to allow them to communicate with each other. Java Application Programming Interface (API) is the area of Java development kit (JDK). An API includes classes, interfaces, packages and also their methods, fields, and constructors.

All these built-in classes give benefits to the programmer. Only programmers understand how to apply that class. A user interface offers the basic user interaction among user and computer, in the same manner, the API works as an application program interface which gives connection amongst the software as well as the consumer. API includes classes and packages which usually assist a programmer to minimize the lines of a program.