Java JRE is the Java Runtime Environment. JRE is used to run web applets, desktop applications, class applications, and any other kind of file that is coded in Java. Without … JRE, you with not be able to use java. Java JDK is the Java Developers Kit.The Java Development Kit is used when developing Java applications.RE is used to run web applets, desktop applications, class applications, and any other kind of file that is coded in Java. Without … JRE, you with not be able to use java. Java JDK is the Java Developers Kit. The Java Development Kit is used when developing Java applications.