CSIS 110 – Lecture 4
Last Time
We started looking at a ticket machine, and started looking at the parts.
- class definition (outer wrapper)
- instance variables/fields
- declaration statements
- constructor
- parameters
oformal
oactual
Assignment
As we saw, we need to store the short-lived value of the parameter into a field so we can
remember it later.
This is done with an assignment statement. For example,
price = ticketCost;
There are three parts in an assignment statement:
1) The left hand side
2) The right hand side
3) An assignment operator – in this case ‘=’
The right-hand side is an expression. Java evaluates the right-hand side and stores the
result in the variable on left-hand side.
In this case, the expression is just a single variable, so Java copies the value from it and
puts it into price. (In general, the expression can be more complex).
An important rule: The type of the expression must match the type of the variable. What
types do we know about?
So, this means that we CAN NOT assign a String to an int, or an int to a boolean.
The same rule applies for formal and actual parameters – their types must match.
Even though the assignment statement uses the ‘=’, don’t confuse this with mathematical
equality.
Examples:
[Have students take a minute or two to work these out themselves (in pairs)]
