The Java Development Kit includes the Java Run-time Environment (JRE) (JDK). It's a free software package that consists of a Java Class Library, tools, and a separate JVM. It is the most prevalent environment for running Java apps on mobile devices. Compilation and conversion of source Java code to Java bytecode are performed. JRE is required if you want to run this bytecode on any platform. The JRE runs classes, verifies memory access, and gets resources. JRE operates on top of an operating system as a layer. It also contains technologies for implementation, such as Java Web Start and user interface toolkits, such as Java 2D.