13.5: Flag Variables
- Page ID
- 15239
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To store a true
or false
value, you need a boolean
variable. You can create one like this:
boolean flag; flag = true; boolean testResult = false;
The first line is a variable declaration, the second is an assignment, and the third is both. Since relational operators evaluate to a boolean
value, you can store the result of a comparison in a variable:
boolean evenFlag = (n % 2 == 0); // true if n is even boolean positiveFlag = (x > 0); // true if x is positive
The parentheses are unnecessary, but they make the code easier to read. A variable defined in this way is called a flag, because it signals or “flags” the presence or absence of a condition.
You can use flag variables as part of a conditional statement later:
if (evenFlag) { System.out.println("n was even when I checked it"); }
Notice that you don’t have to write if (evenFlag == true)
. Since evenFlag
is a boolean
, it’s already a condition. Likewise, to check if a flag is false
:
if (!evenFlag) { System.out.println("n was odd when I checked it"); }