JDK, JRE and JVM: Which One You Actually Install

Three acronyms turn up in every installation guide, in the same sentence, as though the difference were obvious. It is not, and picking the wrong one leaves you with a machine that can run Java and cannot compile it.

What each of the three is, and what it contains
Name	What it is	Contains	You need it to
JVM — Java Virtual Machine	The engine that executes bytecode	Nothing else; it is the innermost piece	Run bytecode, and nothing more
JRE — Java Runtime Environment	The JVM plus the standard library	The JVM, plus `String`, `List`, files, networking	Run a program somebody else compiled
JDK — Java Development Kit	The JRE plus the tools that make bytecode	The JRE, plus `javac`, `jar`, `jshell`, a debugger	Compile anything at all

They nest. Every JDK contains a JRE, and every JRE contains a JVM. Nothing contains a JDK, which is why installing the smallest one leaves you stuck.

The JDK contains the JRE, which contains the JVM

The decision rule. On any machine where you write code, install the JDK. On a machine that only runs a jar somebody else built — a container image, a server — a JRE is enough and is smaller. If you are unsure which of the two a machine is, it is a development machine and it wants the JDK.