JRE is the abbreviation of Java runtime environment. To use Java programs, JRE is an indispensable environment. Jre-java rutime environment java bytecode running environment, jdk-java Developer's Kit is a necessary java development kit for running java programs. In short, the java source code you wrote must be compiled into a. class file with the compiler provided by jdk before it can be executed by Jre. jdk includes jre running environment.