The following code
String[] values = ...
....
Map<String, Object> map = new HashMap<>();
for (int i = 0; i < values.length; i++) {
map.put("X" + i, values[i]);
}
is converted by IntelliJ to:
Map<String, Object> map = IntStream.range(0, values.length)
.collect(Collectors.toMap(
i -> "X" + i,
i -> values[i],
(a, b) -> b));
which can be shortened to
Map<String, Object> map = IntStream.range(0, values.length)
.collect(Collectors.toMap(
i -> "X" + i,
i -> values[i]));
The 2 stream versions don't compile.
IntelliJ, hints that there is an issue with the i in values[i]:
Incompatible types.
Required: int
Found: java.lang.Object
The compiler complains:
Error:(35, 17) java: method collect in interface java.util.stream.IntStream cannot be applied to given types;
required: java.util.function.Supplier,java.util.function.ObjIntConsumer,java.util.function.BiConsumer
found: java.util.stream.Collector>
reason: cannot infer type-variable(s) R
(actual and formal argument lists differ in length)
Can anyone explain why?
Not very certain about how intelliJ's suggestion would work there, it seems inconsistent. Just put a
System.out.print(map);
statement between the declaration and loop and then it won't suggest you Replace with collect any further.
While using the IntStream#collect
, the compilation fails for the reason that implementation of collect
method expects three specified arguments as visible in the error as well while the
Collectors.toMap(i -> "X" + i, i -> values[i])
would result in only a single argument of type Collector
.
Better way to convert the expression would be though to
either use forEach
Map<String, Object> map;
IntStream.range(0, values.length).forEach(i -> map.put("X" + i, values[i]));
Or use boxed()
to convert the IntStream
to Stream<Integer>
as:-
Map<String, Object> map = IntStream.range(0, values.length).boxed()
.collect(Collectors.toMap(i -> "X" + i, i -> values[i], (a, b) -> b));
Or as suggested by @Holger, you can avoid using forEach and boxing overhead and modify the construct to make use of the IntStream.collect
three-arg variant as:-
Map<String, Object> map = IntStream.range(0, values.length)
.collect(HashMap::new, (m,i) -> m.put("X"+i,values[i]), Map::putAll);
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With