JDK vs JRE

JDK: The JDK includes the compiler and other tools needed to develop Java applications

JRE: JRE is a subset of JDK(light weight), it contains java.exe which is used to run an already compiled java application. Unlike JDK, JRE does not include java tools like compiler or other tools. 

JDK vs JRE: JDK is a superset of JRE, it can be used to develop java applications, compiling and running java applications. JRE is just for running already compiled application.