The JRE or Java runtime allows you to run Java code. Without the JRE it is impossible to run any programs written in Java. This means that the end user must have JRE installed on their PC. This can be downloaded from the http://java.sun.com website or from your linux repositories.
Java enabled mobile phones will already have the JRE installed (or a cut down version of it) in order to run Java mobile edition (JME),
Compiled Java code comes in the form of class files or JAR files (archive of Java files). A Java virtual machine will then run the class files. The virtual machine represents a kind of generic computer which allows all Java programs to behave in the same way. As the diagram below demonstrates -
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