java jre confusion

Question

Could anyone please tell how jre directory help in the running java programs? I'm calling java interpretor by using java command, and that is in JDK directory, then how could jre directory help in running java programs and jdk for compiling?

Answer 1

When you install the JDK (development kit, compiler and so on), you get the JRE (runtime environment) as part of that (under my install, there's actually a jre subdirectory in the jdk folder) - this is because you will probably want to run code that you develop if only to test it a little bit before inflicting it on the rest of the planet :-).

But it's by no means necessary to install the JDK to run Java programs. All you need is the JRE and that is, by far, the normal situation for most people out there.

Answer 2

The Java Runtime Environment (JRE) interprets byte code to platform specific machine code. JRE is minimal set of programmes which executes the java class files.

The JDK (Java Developmental Toolkit) comes along with java libraries and JRE embedded in it. Apart from these it comes along with the utility tools for byte code compilation "javac".

Answer 3

The JRE is just the interpreter (java.exe or whatever) - it's a smaller install that is typically used by people who just need to run Java applications and aren't Java developers. The JRE handles the conversion and execution of java bytecode for the target platform.

The JDK is meant for developers. Along with the runtime it provides the compiler and all the Java libraries that are used to build Java programs. The compiler is responsible for converting Java source code to bytecode.

So - when you are delivering your Java application to customers, all they need to install is the JRE.