Java Reference
In-Depth Information
to implement the single responsibility principle at the method level. Let's take a look at some
code that counts the number of prime numbers up to a certain value (
Example 8-34
)
.
Example 8-34. Counting prime numbers with multiple responsibilities in a method
public
public
long
long
countPrimes
(
int
int
upTo
) {
long
long
tally
=
0
;
for
for
(
int
int
i
=
1
;
i
<
upTo
;
i
++) {
boolean
boolean
isPrime
=
true
true
;
for
for
(
int
int
j
=
2
;
j
<
i
;
j
++) {
iif
(
i
%
j
==
0
) {
isPrime
=
false
false
;
}
}
iif
(
isPrime
) {
tally
++;
}
}
return
return
tally
;
}
It's pretty obvious that we're really doing two things in
Example 8-34
:
we're counting num-
bers with a certain property and we're checking whether a number is a prime. As shown in
Example 8-35
,
we can easily refactor this to split apart these two responsibilities.
Example 8-35. Counting prime numbers after refactoring out the isPrime check
public
public
long
long
countPrimes
(
int
int
upTo
) {
long
long
tally
=
0
;
for
for
(
int
int
i
=
1
;
i
<
upTo
;
i
++) {
iif
(
isPrime
(
i
)) {
tally
++;
}
}
return
return
tally
;
}
private
private
boolean
boolean
isPrime
(
int
int
number
) {
for
for
(
int
int
i
=
2
;
i
<
number
;
i
++) {
iif
(
number
%
i
==
0
) {
return
return false
false
;
}
}
return
return true
true
;
}
