1, jvm: java virtual machine responsible for translating .class binary files into machine instructions operate on different systems. Therefore, to achieve a cross-platform java JVM is running, it can recognize it .class file translation into different machines operating instructions on different platforms, can run on windows, linux finest different platforms. jvm responsible class file is loaded into memory, which contains a class loader subsystem, the runtime data areas: the method area (new target) (static region), heap, stack (local variables and intermediate results of the method), the program counter, local method, the garbage collection system, the execution engine.
2, jre: java runtime environment, which includes jvm and java project needs to run java class libraries, java.util java.sql java.long java.net and so on. If you do not compile and run only, then there can be a jre, java command responsible for pull JVM.
3, jdk: contains tools and compilers and other development jre java project need, these tools are the bin directory under the installed jdk, including javac.exe java.exe jar.exe jvisiovm.exe, jconsole and other responsible for compiling, operation and project commissioning.