The JDK is a key platform component for building Java applications. At its heart is the Java compiler

The Java Development Kit (JDK) is one of three core technology packages used in Java programming, along with the JVM (Java Virtual Machine) and the JRE (Java Runtime Environment). It’s important to differentiate between these three technologies, as well as understanding how they’re connected:
The JVM is the Java platform component that executes programs.
The JRE is the on-disk part of Java that creates the JVM.
The JDK allows developers to create Java programs that can be executed and run by the JVM and JRE.
Developers new to Java often confuse the Java Development Kit and the Java Runtime Environment. The distinction is that the JDK is a package of tools for developing Java-based software, whereas the JRE is a package of tools for running Java code.