Additional Libraries(In the lib/ subdirectory) Additional class libraries and support files required by the development tools.
The JRE includes a Java Virtual Machine (JVM), class libraries, and other files that support the execution of programs written in the Java programming language.
Java Development Kit contains the software and tools that you need to compile, debug, and run applets and applications written using the Java programming language. Java Development Kit is the official development kit for the Java programming language.