Unit 6 · Ends the course
Breaking a program into named pieces, then grouping data and behavior together into a class. This is the unit that makes larger programs possible rather than merely longer.
Know
A method takes values, does one job, and usually hands something back. Deciding what it takes and returns is the design; the body is the easy part.
Apply
Write the name, the values it takes, and what it returns before the body.
Watch out
Writing one long method that does several jobs, which is hard to test and harder to fix.
Know
Returning gives a value to whoever called the method. Printing shows it on screen and hands back nothing usable.
Apply
Return the result and let the caller decide whether to print it.
Watch out
Printing inside a method and then trying to use the result, which gives nothing.
Know
A class describes a kind of thing; an object is one of them. The constructor sets up a new object when it is created.
Apply
Give every piece of data a value in the constructor so no object starts incomplete.
Watch out
Writing a return type on a constructor, which turns it into an ordinary method that never runs.
Know
Keeping data private and offering methods to work with it lets the object stay in a sensible state.
Apply
Make the data private and add only the operations that make sense for the thing.
Watch out
Making everything public, which lets any code put the object into a nonsense state.
Know
Searching one item at a time works on any order. Searching by halving requires the data to be sorted first.
Apply
Check whether data is sorted before choosing the faster method.
Watch out
Halving through unsorted data, which gives a wrong answer without any error.
Know
Programs that store information about people carry responsibilities, including privacy and fairness.
Apply
For any program holding personal data, say what it stores, why it needs it, and who can see it.
Watch out
Collecting data because it is easy rather than because it is needed.
Connections and techniques that receive extra attention in this unit.
Related topics some schools attach to this unit and others leave out. Covered on request rather than assumed.
Modeling drill
Write a class that stores a student name and a list of scores, with a method returning the average, keeping the scores private.
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