What is the difference between a java class file and a jar file?
A JAR file has many files into it. We generally use .jar files to distribute Java applications or libraries, in the form of Java class files and associated metadata and resources (text, images, etc.). you can say JAR = Java ARchive.
All java files are compiled into class files and then we use that class file not the .java file. A class is a construct that is used as a blueprint to create instances of the class.
See Wikipedia for more information: Wikipedia for JAR and Wikipedia for class