[英]Java stream map create objects with counter
I am new to Java and its stream capabilities. 我是Java及其流功能的新手。 How can this loop functionality be achieved with stream instead of the loop: 如何使用流而不是循环实现此循环功能:
List<PackageData> packages = new ArrayList<>();
for(int i = 0; i < 100; i++) {
PackageData packageData = ImmutablePackageData.builder()
.withPackageGroup("ConstantString")
.withPackageType("ConstantString")
.withTrackingId("ConstantString" + i.toString())
.withLocationId("ConstantString" + i.toString())
.build();
packages.add(packageData);
}
You can utilize IntStream
; 你可以使用IntStream
;
List<PackageData> packages = IntStream.range(0, 100)
.mapToObj(i -> ImmutablePackageData.builder()
.withPackageGroup("ConstantString")
.withPackageType("ConstantString")
.withTrackingId("ConstantString" + i)
.withLocationId("ConstantString" + i)
.build())
.collect(Collectors.toList())
Since your stream depends on nothing but a range of integer [0, 100)
因为你的流只依赖于整数范围[0, 100)
check IntStream#range
, and IntStream#mapToObj
检查IntStream#range
和IntStream#mapToObj
From jdk-9 you can also use stream.iterate() to generate sequential stream 从jdk-9开始,您还可以使用stream.iterate()生成顺序流
static <T> Stream<T> iterate(T seed,
Predicate<? super T> hasNext,
UnaryOperator<T> next)
Example 例
List<PackageData> packages = Stream.iterate(0, i->i<100, i->i+1)
.map(i-> -> ImmutablePackageData.builder()
.withPackageGroup("ConstantString")
.withPackageType("ConstantString")
.withTrackingId("ConstantString" + i)
.withLocationId("ConstantString" + i)
.build())
.collect(Collectors.toList())
I'd use Stream.iterate
我使用Stream.iterate
List<PackageData> packages = Stream.iterate(0, (index) -> ImmutablePackageData.builder()
.withPackageGroup("ConstantString")
.withPackageType("ConstantString")
.withTrackingId("ConstantString" + index)
.withLocationId("ConstantString" + index)
.build())
.limit(100)
.collect(Collectors.toList());
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