When the call to a function doesn’t have any side effects, what is the point of making the call if the results are ignored? In such case, either
the function call is useless and should be dropped or the source code doesn’t behave as expected.
To prevent generating any false-positives, this rule triggers an issue only on the following predefined list of immutable classes in the Java API
:
-
java.lang.String
-
java.lang.Boolean
-
java.lang.Integer
-
java.lang.Double
-
java.lang.Float
-
java.lang.Byte
-
java.lang.Character
-
java.lang.Short
-
java.lang.StackTraceElement
-
java.time.DayOfWeek
-
java.time.Duration
-
java.time.Instant
-
java.time.LocalDate
-
java.time.LocalDateTime
-
java.time.LocalTime
-
java.time.Month
-
java.time.MonthDay
-
java.time.OffsetDateTime
-
java.time.OffsetTime
-
java.time.Period
-
java.time.Year
-
java.time.YearMonth
-
java.time.ZonedDateTime
-
java.math.BigInteger
-
java.math.BigDecimal
-
java.util.Optional
As well as methods of the following classes:
-
java.util.Collection:
-
size()
-
isEmpty()
-
contains(...)
-
containsAll(...)
-
iterator()
-
toArray()
-
java.util.Map:
-
size()
-
isEmpty()
-
containsKey(...)
-
containsValue(...)
-
get(...)
-
getOrDefault(...)
-
keySet()
-
entrySet()
-
values()
-
java.util.stream.Stream
-
toArray
-
reduce
-
collect
-
min
-
max
-
count
-
anyMatch
-
allMatch
-
noneMatch
-
findFirst
-
findAny
-
toList
Noncompliant code example
public void handle(String command){
command.toLowerCase(); // Noncompliant; result of method thrown away
...
}
Compliant solution
public void handle(String command){
String formattedCommand = command.toLowerCase();
...
}
Exceptions
This rule will not raise an issue when both these conditions are met:
- The method call is in a
try block with an associated catch clause.
- The method name starts with "parse", "format", "decode" or "valueOf" or the method is
String.getBytes(Charset).
private boolean textIsInteger(String textToCheck) {
try {
Integer.parseInt(textToCheck, 10); // OK
return true;
} catch (NumberFormatException ignored) {
return false;
}
}
