This is a frequently asked question in Oracle interview questions. The javac command reads source files containing Java module, package, and type declarations and compiles them into class files that operate on the Java Virtual Machine. Annotations in Java source files and classes can also be processed by the javac command.  In Java, a Wrapper class is a type of class that offers a method for converting primitive data types into objects and vice versa. When a wrapper class is constructed, a new field is generated in which the primitive data types are stored.