昨天給大家介紹了Java 16中的Stream增強，可以直接通過toList()來轉換成List。
主要涉及下面這幾種轉換方式：
list.stream().toList();
list.stream().collect(Collectors.toList());
list.stream().collect(Collectors.toUnmodifiableList());然後，看到有網友評論問：Stream.toList()和Collectors.toList()的區別是什麼？哪個效能好？
處理結果的區別，其實上一篇文章和視訊裡都有說：
Stream.toList()返回的List是不可變List，不能增刪改Collectors.toList()返回的是個普通的List，可以增刪改Collectors.toUnmodifiableList()返回的List是不可變List，不能增刪改
而至於效能的話，今天我們就來測試一下，看看哪個效能更好。
@BenchmarkMode(Mode.All)
@Fork(1)
@State(Scope.Thread)
@Warmup(iterations = 20, time = 1, batchSize = 10000)
@Measurement(iterations = 20, time = 1, batchSize = 10000)
public class BenchmarkStreamToList {
@Benchmark
public List<Integer> streamToList() {
return IntStream.range(1, 1000).boxed().toList();
}
@Benchmark
public List<Integer> collectorsToList() {
return IntStream.range(1, 1000).boxed().collect(Collectors.toList());
}
@Benchmark
public List<Integer> streamToList() {
return IntStream.range(1, 1000).boxed().toList();
}
}結果報告：
Benchmark Mode Cnt Score Error Units
BenchmarkStreamToList.collectorsToList thrpt 20 24.422 ± 0.268 ops/s
BenchmarkStreamToList.collectorsToUnmodifiableList thrpt 20 22.784 ± 0.599 ops/s
BenchmarkStreamToList.streamToList thrpt 20 31.779 ± 1.732 ops/s
BenchmarkStreamToList.collectorsToList avgt 20 0.045 ± 0.006 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList avgt 20 0.062 ± 0.035 s/op
BenchmarkStreamToList.streamToList avgt 20 0.040 ± 0.028 s/op
BenchmarkStreamToList.collectorsToList sample 445 0.046 ± 0.002 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.00 sample 0.039 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.50 sample 0.041 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.90 sample 0.057 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.95 sample 0.073 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.99 sample 0.102 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.999 sample 0.150 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.9999 sample 0.150 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p1.00 sample 0.150 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList sample 460 0.044 ± 0.001 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.00 sample 0.042 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.50 sample 0.044 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.90 sample 0.046 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.95 sample 0.047 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.99 sample 0.051 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.999 sample 0.057 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.9999 sample 0.057 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p1.00 sample 0.057 s/op
BenchmarkStreamToList.streamToList sample 655 0.031 ± 0.001 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.00 sample 0.030 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.50 sample 0.031 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.90 sample 0.032 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.95 sample 0.033 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.99 sample 0.035 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.999 sample 0.037 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.9999 sample 0.037 s/op
BenchmarkStreamToList.streamToList:streamToList·p1.00 sample 0.037 s/op
BenchmarkStreamToList.collectorsToList ss 20 0.043 ± 0.001 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList ss 20 0.045 ± 0.004 s/op
BenchmarkStreamToList.streamToList ss 20 0.031 ± 0.001 s/op從報告中我們可以看到：
- 吞吐量：
streamToList>collectorsToList>collectorsToUnmodifiableList - 平均耗時：
streamToList>collectorsToList>collectorsToUnmodifiableList - p0.9999耗時：
streamToList>collectorsToUnmodifiableList>collectorsToList - 冷啟動耗時：
streamToList>collectorsToList>collectorsToUnmodifiableList
所以，Stream.toList()的效能要各方面都要好於Collectors.toList()和Collectors.toUnmodifiableList()。
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再放大一些資料量，試試：
@Benchmark
public List<Integer> streamToList() {
return IntStream.range(1, 10000).boxed().toList();
}
@Benchmark
public List<Integer> collectorsToList() {
return IntStream.range(1, 10000).boxed().collect(Collectors.toList());
}
@Benchmark
public List<Integer> streamToList() {
return IntStream.range(1, 10000).boxed().toList();
}結果報告：
Benchmark Mode Cnt Score Error Units
BenchmarkStreamToList.collectorsToList thrpt 20 2.186 ± 0.162 ops/s
BenchmarkStreamToList.collectorsToUnmodifiableList thrpt 20 2.184 ± 0.042 ops/s
BenchmarkStreamToList.streamToList thrpt 20 3.538 ± 0.058 ops/s
BenchmarkStreamToList.collectorsToList avgt 20 0.426 ± 0.004 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList avgt 20 0.469 ± 0.016 s/op
BenchmarkStreamToList.streamToList avgt 20 0.293 ± 0.008 s/op
BenchmarkStreamToList.collectorsToList sample 58 0.448 ± 0.049 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.00 sample 0.414 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.50 sample 0.422 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.90 sample 0.458 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.95 sample 0.560 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.99 sample 1.160 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.999 sample 1.160 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p0.9999 sample 1.160 s/op
BenchmarkStreamToList.collectorsToList:collectorsToList·p1.00 sample 1.160 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList sample 60 0.458 ± 0.004 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.00 sample 0.447 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.50 sample 0.455 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.90 sample 0.471 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.95 sample 0.482 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.99 sample 0.492 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.999 sample 0.492 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p0.9999 sample 0.492 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList:collectorsToUnmodifiableList·p1.00 sample 0.492 s/op
BenchmarkStreamToList.streamToList sample 78 0.293 ± 0.012 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.00 sample 0.277 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.50 sample 0.284 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.90 sample 0.309 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.95 sample 0.377 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.99 sample 0.459 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.999 sample 0.459 s/op
BenchmarkStreamToList.streamToList:streamToList·p0.9999 sample 0.459 s/op
BenchmarkStreamToList.streamToList:streamToList·p1.00 sample 0.459 s/op
BenchmarkStreamToList.collectorsToList ss 20 0.474 ± 0.133 s/op
BenchmarkStreamToList.collectorsToUnmodifiableList ss 20 0.493 ± 0.099 s/op
BenchmarkStreamToList.streamToList ss 20 0.325 ± 0.056 s/op從報告中我們可以看到
- 吞吐量：
streamToList>collectorsToList>collectorsToUnmodifiableList - 平均耗時：
streamToList>collectorsToList>collectorsToUnmodifiableList - p0.9999耗時：
streamToList>collectorsToUnmodifiableList>collectorsToList - 冷啟動耗時：
streamToList>collectorsToList>collectorsToUnmodifiableList
所以，即使集合內的元素增大，Stream.toList()的效能在各方面依然都要好於Collectors下的方法。
好了，今天的分享就到這裡，你學會了嗎？
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