The JRE structure

When you install the Java 8 Runtime Environment on any machine and examine the installed directory, you'll see, among other files and folders, the following two important directories:

• A bin directory with executable files, an important one of which is the Java executable that lets you run Java programs
• The lib directory with some key .jar files including the all-important rt.jar

You may not have had to deal with the rt.jar directly when coding in Java, but you should know that it's the single most important jar file in the runtime. Can you guess what it's for?