Unit 1 · Take your time
Storing values and doing arithmetic with them. Java asks you to say what kind of value each variable holds, which feels like extra work for about a week and then starts catching your mistakes for you.
Know
A variable is a named box holding one value, and in Java you declare what kind of value it holds. A whole number and a decimal number are different kinds and behave differently.
Apply
Declare the type that matches the data: whole counts as int, measurements as double, yes-or-no as boolean.
Watch out
Storing a measurement as a whole number, which quietly throws away the decimal part.
Know
When two whole numbers are divided, Java gives a whole number back and throws away the remainder. It does not round; it cuts.
Apply
Use division for how many fit and the remainder operator for what is left over.
Watch out
Expecting 7 divided by 2 to be 3.5. Between two whole numbers it is 3, and this surprises nearly everyone once.
Know
A cast tells Java to treat a value as a different type. Where you put it changes the answer, because it applies to what comes immediately after.
Apply
Do the arithmetic first and cast afterwards when you want the decimal work to happen.
Watch out
Casting too early, which throws away the decimals before they were used.
Know
The plus sign adds numbers but joins text. Once text appears, everything after it is joined rather than added.
Apply
Put brackets around arithmetic that must happen before the joining.
Watch out
Getting two digits stuck together instead of their sum, because text came first in the line.
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 turns a number of seconds into minutes and leftover seconds, then check it on 0, 59, and 61.
Work through questions with a tutor and get help with the steps you find difficult.
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