The unary operator NOT, !
, works on a single value. This operator evaluates to the opposite boolean to which it’s applied:
!false // true !true // false
NOT is useful for expressing our intent clearly in programs. For example, sometimes we need the opposite behavior of an if-then
: run a code block only if the condition is false
.
boolean hasPrerequisite = false; if (hasPrerequisite) { // do nothing } else { System.out.println("Must complete prerequisite course!"); }
This code does what we want but it’s strange to have a code block that does nothing!
The logical NOT operator cleans up our example:
boolean hasPrerequisite = false; if (!hasPrerequisite) { System.out.println("Must complete prerequisite course!"); }
We can write a succinct conditional statement without an empty code block.
Instructions
Let’s make informUser()
more informative. If their reservation is not confirmed, they should know!
Write an if-then-else
statement and use !
with isConfirmed
as the condition.
If their reservation is not confirmed, write Unable to confirm reservation, please contact restaurant.
Else write: Please enjoy your meal!