What is the difference between JDK and JRE?

It's a Java development tool. It contains compilers, etc. necessary for Java programming. Non-Java programmers do not need to download. If JDK is installed, JRE below is also installed.

Creating a Java environment where compiled Java programs can run.

JRE must be installed to run the Java program.

There is no Java programming tool in JRE. To do Java programming, you need to get the above JDK. Both are free.