TASC Computer Science help

The course document is unusually specific about Java. It lists primitive types with promotion and casting, arithmetic and logic operators including the modulus, classes and information hiding, arrays and strings, control flow, methods and scope, GUI widgets, and events and listeners using the AWT library. Since the 2022 version, Java applications are compulsory.

It also asks for programming style. Programs should follow a defined set of standards for names, comments and indenting, with style guides such as the Oracle Java Code Conventions and the Google Java Style Guide given as examples, and Javadoc documentation comments recommended.

Area 2 is where many students need the most help. It runs from binary fractions and two's complement arithmetic, through Boolean operators, logic gates and the flip-flop, to the fetch, decode and execute cycle and the role of the Java Virtual Machine.

The computing option leaves room for personal interest. Suggested topics include game development, mobile programming, cryptography, artificial intelligence and machine learning, network programming and programming LEGO robots with LeJOS.

The interesting line is address 13. Five minus eight is minus three, and in a 16-bit word that appears as FFFD. Written in binary it is 1111 1111 1111 1101. Inverting every bit gives 0000 0000 0000 0010, and adding one gives 3, so FFFD is the two's complement representation of minus three. That is the "addition and subtraction only" two's complement arithmetic the course lists, met inside a real program.

Students who trace this table by hand, one row at a time, rarely confuse a register with a memory address again. That confusion, mixing up Format 1 and Format 2, is the most common error we see.

Relating TOY to Java, the top standard in this criterion, is easier than it sounds. Java's short type is also a 16-bit two's complement integer, so short a = 5, b = 8 followed by short d = (short) (a minus b) leaves minus three in d, with the same bit pattern as R[D]. The addition line corresponds to an assignment, the loads and stores to reading and writing variables.

We checked this program in a short simulator we wrote, which steps through each instruction and prints the registers. Writing such a simulator in Java is itself an excellent revision exercise for both halves of the course.