(Adapted from UWCSE501)

• Add additional arithmetic and relational operators for integers that are not included in the basic MiniJava specification.
• Add null as a constant expression and support == and != for object reference types.
• Allow return statements anywhere in a method.
• Allow calls of local methods without the explicit use of this.
• Support methods with more than the required maximum of 5 parameters.
• Relax the ordering of declarations so that variables can be declared anywhere in a method body.
• Allow initialization of variables in declarations.
• Add void methods that do not return a value, a return statement with no expression, and appropriate type checking rules.
• Support public and private declarations on both methods and instance variables, and check to ensure that access restrictions are not violated.
• Add a top-level Object class that is implicitly the superclass of any class that does not explicitly extend another class.
• Add String literals, extend System.out.println to support Strings, and overload the + operator for String values.
• Add double as a numeric type, overload System.out.println to print doubles, and implement arithmetic operations for double, possibly including mixed-mode integer and floating-point arithmetic where integer values are automatically converted to double as needed.
• Support instanceof and type casts (which can require a runtime instanceof check). (This actually is surprisingly easy to do.)
• Support super. as a prefix in method calls.
• Add constructor declarations with optional parameters. To make this useful, you probably want to also include the use of super(...) at the beginning of the body of a constructor.
• Support arrays of objects (no harder to implement than arrays of ints, except the type checking rules are more interesting).