Java is a high-level object-oriented programming language developed by Sun Microsystems, which became part of Oracle Corporation in 2010. The language is very similar to C++, but has been simplified to make it easier to write bug free code. Most notably, there are no pointers in Java, instead all memory allocation and deallocation is handled automatically.
Despite simplifications like this Java has considerably more functionality than both C and C++, due to its large class library. Java programs also have high performance and can be made very secure, which has contributed to making Java the most popular general purpose programming language in use today.
Another key feature of Java is that it is platform independent. This is achieved by only compiling programs half-way, into platform independent instructions called bytecode. The bytecode is then interpreted, or run, by the Java Virtual Machine (JVM). This means that any system that has this program and its accompanying libraries installed can run Java applications.
There are three class libraries available for the Java programming language: Java ME, Java SE and Java EE. Java ME (Mobile Edition) is a stripped down version of Java SE (Standard Edition), while Java EE (Enterprise Edition) is an extended version of Java SE that includes libraries for building web applications.
The Java language and class libraries have undergone major changes since their initial release in 1996. The naming conventions for the versions have gone through a few revisions as well. The major releases include: JDK 1.0, JDK 1.1, J2SE 1.2, J2SE 1.3, J2SE 1.4, J2SE 5.0, Java SE 6 and Java SE 7, which is the current version.
After J2SE 1.4 the version number was changed from 1.5 to 5.0 for marketing reasons. As of J2SE 5.0, there is one version number for the product and another one used internally by the developers. J2SE 5.0 is the product name, while Java 1.5 is the developer version. Similarly, Java SE 7 is the product and Java 1.7 the internal version number. For simplicity’s sake, the Java versions will be referred to as Java 1-7 in this tutorial. Note that Java is designed to be backwards compatible. Thus the Virtual Machine for Java 7 can still run Java 1 class files.
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