Program Logic and Indefinite Loops - Building Java Programs: A Back to Basics Approach - page 331

Suppose you want to call the method isTwoUniqueDigits . You want the method
to take a value of type int and return true if the int is composed of two unique digits
and false if it is not. So, the method would look like the following:
public static boolean isTwoUniqueDigits(int n) {
...
}
How would you write the body of this method? We've already written the test, so
we just have to figure out how to incorporate it into the method. The method has a
boolean return type, so you want it to return the value true when the test succeeds
and the value false when it fails. You can write the method as follows:
public static boolean isTwoUniqueDigits(int n) {
if (n >= 10 && n <= 99 && (n % 10 != n / 10)) {
return true;
} else {
return false;
}
}
This method works, but it is more verbose than it needs to be. The preceding code
evaluates the test that we developed. That expression is of type boolean , which
means that it evaluates to either true or false . The if/else statement tells the
computer to return true if the expression evaluates to true and to return false if it
evaluates to false . But why use this construct? If the method is going to return true
when the expression evaluates to true and return false when it evaluates to false ,
you can just return the value of the expression directly:
public static boolean isTwoUniqueDigits(int n) {
return (n >= 10 && n <= 99 && (n % 10 != n / 10));
}
Even the preceding version can be simplified, because the parentheses are not nec-
essary (although they make it clearer exactly what the method will return). This code
evaluates the test that we developed to determine whether a number is composed of
two unique digits and returns the result ( true when it does, false when it does not).
Consider an analogy to integer expressions. To someone who understands Boolean
Zen, the if/else version of this method looks as odd as the following code:
if (x == 1) {
return 1;
} else if (x == 2) {
return 2;
} else if (x == 3) {
return 3;