Unit 2 · Steady
Teaching a program to choose. The syntax is short; the difficulty is writing conditions that are true exactly when you meant them to be, especially at the edges of a range.
What a strong answer looks like
A strong Unit 2 answer checks the condition at its exact boundary rather than at a comfortable value in the middle.
Know
A comparison produces true or false. And requires both parts true; or requires at least one; not flips the answer.
Apply
Work out each part separately, then combine them.
Watch out
Reading a condition as an English sentence rather than evaluating each comparison.
Study move
Write a condition with two comparisons and work out its value for four different inputs.
Know
An if-else chain runs at most one branch. Separate ifs can all run. The order matters when the ranges touch.
Apply
Check what happens at each boundary value, not just inside each range.
Watch out
Putting a wide condition first, so a later specific one can never be reached.
Study move
Trace a grade classifier at 79, 80, 89, and 90.
Know
A range check needs two comparisons joined together. Java will not accept the shorthand used in mathematics.
Apply
Write both comparisons explicitly and join them.
Watch out
Writing a chained comparison as you would on paper, which Java rejects or misreads.
Study move
Write a check for an age between 13 and 19 and test both ends.
Know
Java stops checking a condition once the answer is settled, which lets an earlier check protect a later one.
Apply
Put the safety check first so the risky part is never reached when it would fail.
Watch out
Putting the checks in the wrong order, so the thing that crashes runs before the check meant to stop it.
Study move
Write a condition that checks something exists before looking inside it, then swap the order and explain the crash.
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 program that reports whether a score is a pass, a merit, or a distinction, and check every boundary value.
