The Java RUNTIME Environment consists of the Java Virtual Machine, supporting files and core classes. This is basically the minimum requirements to execute a Java application. The JRE is actually a component of the JDK but it can be downloaded separately from the rest.

Some of the components of the JRE are given as follows:

1. User Interface Toolkits such as Java 2D, AWT, Sound, Swing etc.
2. Java Virtual Machine and Server Virtual Machines.
3. Lang and Util base libraries such as Zip, Collections, Versioning etc.
4. Deployment techniques
5. Base libraries such as I/O, Beans, JNI, Networking etc.

The Java programs are executed by the Java Virtual Machine which is a running software system. The Java Runtime Environment on the other hand, is a on-disk system that starts the JVM to execute the Java code by combining it with the required libraries.

In short, the software and libraries that are necessary to run the Java programs are CONTAINED in the Java Runtime Environment.

A diagram that demonstrates that the JRE contains the JVM is given as follows:

The Java Runtime Environment is essentially a software that is installed on the computer that runs the Java programs. Normally, Java is installed on the computer and the JRE is included. HOWEVER, if anytime it is required to install or upgrade the JRE manually, it can be done by downloading the current JRE VERSION from Oracle.