Java is a programming language created by James Gosling from Sun Microsystems (Sun) in 1991. The target of Java is to write a program once and then run this program on multiple operating systems. The first publicly available version of Java (Java 1.0) was released in 1995. Sun Microsystems was acquired by the Oracle Corporation in 2010. Oracle has now the steermanship for Java. In 2006 Sun started to make Java available under the GNU General Public License (GPL). Oracle continues this project called Open
or time new enhanced versions of Java have been released. The current version of Java is Java 1.8 which is also known as Java 8.
Java is defined by a specification and consists of a programming language, a compiler, core libraries and a runtime (Java virtual machine) The Java runtime allows software developers to write program code in other languages than the Java programming language which still runs on the Java virtual machine. The Java platform is usually associated with the Java virtual machine and the Java core libraries.
The Java language was designed with the following properties:
Platform independent: Java programs use the Java virtual machine as abstraction and do not access the operating system directly. This makes Java programs highly portable. A Java program (which is standard-compliant and follows certain rules) can run unmodified on all supported platforms, e.g., Windows or Linux.
Object-orientated programming language: Object-oriented means we organize our software as a combination of different types of objects that incorporates both data and behaviour.
Object-oriented programming(OOPs) is a methodology that simplify software development and maintenance by providing some rules.
Basic concepts of OOPs are:
Interpreted and compiled language: Java source code is transferred into the bytecode format which does not depend on the target platform. These bytecode instructions will be interpreted by the Java Virtual machine (JVM). The JVM contains a so called Hotspot-Compiler which translates performance critical bytecode instructions into native code instructions.
Java is secured because:
No explicit pointer
Java Programs run inside virtual machine sandbox
Classloader: adds security by separating the package for the classes of the local file system from those that are imported from network sources.
Bytecode Verifier: checks the code fragments for illegal code that can violate access right to objects.
Security Manager: determines what resources a class can access such as reading and writing to the local disk.
These security are provided by java language. Some security can also be provided by application developer through SSL, JAAS, Cryptography etc.
Robust simply means strong. Java uses strong memory management. There are lack of pointers that avoids security problem. There is automatic garbage collection in java. There is exception handling and type checking mechanism in java. All these points makes java robust.
Java is faster than traditional interpretation since byte code is “close” to native code still somewhat slower than a compiled language (e.g., C++).
A thread is like a separate program, executing concurrently. We can write Java programs that deal with many tasks at once by defining multiple threads. The main advantage of multi-threading is that it doesn’t occupy memory for each thread. It shares a common memory area. Threads are important for multi-media, Web applications etc.
We may carry the java bytecode to any platform.