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繁星淼淼
Map<String, String> map = ...for (Map.Entry<String, String> entry : map.entrySet()) {
System.out.println(entry.getKey() + "/" + entry.getValue());}
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翻翻过去那场雪
为了总结其他答案并将它们与我所知道的结合起来,我找到了10种主要方法(见下文)。另外,我写了一些性能测试(见下面的结果)。例如,如果我们想要找到地图的所有键和值的总和,我们可以写:使用iterator和Map.Entrylong i = 0;Iterator<Map.Entry<Integer, Integer>> it = map.entrySet().iterator();while (it.hasNext()) {
Map.Entry<Integer, Integer> pair = it.next();
i += pair.getKey() + pair.getValue();}使用foreach和Map.Entrylong i = 0;for (Map.Entry<Integer, Integer> pair : map.entrySet()) {
i += pair.getKey() + pair.getValue();}使用Java 8中的forEachfinal long[] i = {0};map.forEach((k, v) -> i[0] += k + v);使用keySet和foreachlong i = 0;for (Integer key : map.keySet()) {
i += key + map.get(key);}使用keySet和iteratorlong i = 0;Iterator<Integer> itr2 = map.keySet().iterator();while (itr2.hasNext()) {
Integer key = itr2.next();
i += key + map.get(key);}使用for和Map.Entrylong i = 0;for (Iterator<Map.Entry<Integer, Integer>> entries = map.entrySet().iterator(); entries.hasNext(); ) {
Map.Entry<Integer, Integer> entry = entries.next();
i += entry.getKey() + entry.getValue();}使用Java 8 Stream APIfinal long[] i = {0};map.entrySet().stream().forEach(e -> i[0] += e.getKey() + e.getValue());使用Java 8 Stream API并行final long[] i = {0};map.entrySet().stream().parallel().forEach(e -> i[0] += e.getKey() + e.getValue());使用IterableMap的Apache Collectionslong i = 0;MapIterator<Integer, Integer> it = iterableMap.mapIterator();while (it.hasNext()) {
i += it.next() + it.getValue();}使用Eclipse(CS)集合的MutableMapfinal long[] i = {0};mutableMap.forEachKeyValue((key, value) -> {
i[0] += key + value;});性能测试(模式= AverageTime,system = Windows 8.1 64位,Intel i7-4790 3.60 GHz,16 GB)对于小地图(100个元素),得分0.308是最好的Benchmark Mode Cnt Score Error Unitstest3_UsingForEachAndJava8
avgt 10 0.308 ± 0.021 µs/op
test10_UsingEclipseMap avgt 10 0.309 ± 0.009 µs/op
test1_UsingWhileAndMapEntry avgt 10 0.380 ± 0.014 µs/op
test6_UsingForAndIterator avgt 10 0.387 ± 0.016 µs/op
test2_UsingForEachAndMapEntry avgt 10 0.391 ± 0.023 µs/op
test7_UsingJava8StreamApi avgt 10 0.510 ± 0.014 µs/op
test9_UsingApacheIterableMap avgt 10 0.524 ± 0.008 µs/op
test4_UsingKeySetAndForEach avgt 10 0.816 ± 0.026 µs/op
test5_UsingKeySetAndIterator avgt 10 0.863 ± 0.025 µs/op
test8_UsingJava8StreamApiParallel avgt 10 5.552 ± 0.185 µs/op对于10000个元素的地图,得分37.606是最好的Benchmark Mode Cnt Score Error Unitstest10_UsingEclipseMap
avgt 10 37.606 ± 0.790 µs/op
test3_UsingForEachAndJava8 avgt 10 50.368 ± 0.887 µs/op
test6_UsingForAndIterator avgt 10 50.332 ± 0.507 µs/op
test2_UsingForEachAndMapEntry avgt 10 51.406 ± 1.032 µs/op
test1_UsingWhileAndMapEntry avgt 10 52.538 ± 2.431 µs/op
test7_UsingJava8StreamApi avgt 10 54.464 ± 0.712 µs/op
test4_UsingKeySetAndForEach avgt 10 79.016 ± 25.345 µs/op
test5_UsingKeySetAndIterator avgt 10 91.105 ± 10.220 µs/op
test8_UsingJava8StreamApiParallel avgt 10 112.511 ± 0.365 µs/op
test9_UsingApacheIterableMap avgt 10 125.714 ± 1.935 µs/op对于具有100000个元素的地图,得分1184.767是最好的Benchmark Mode Cnt Score Error Unitstest1_UsingWhileAndMapEntry
avgt 10 1184.767 ± 332.968 µs/op
test10_UsingEclipseMap avgt 10 1191.735 ± 304.273 µs/op
test2_UsingForEachAndMapEntry avgt 10 1205.815 ± 366.043 µs/op
test6_UsingForAndIterator avgt 10 1206.873 ± 367.272 µs/op
test8_UsingJava8StreamApiParallel avgt 10 1485.895 ± 233.143 µs/op
test5_UsingKeySetAndIterator avgt 10 1540.281 ± 357.497 µs/op
test4_UsingKeySetAndForEach avgt 10 1593.342 ± 294.417 µs/op
test3_UsingForEachAndJava8 avgt 10 1666.296 ± 126.443 µs/op
test7_UsingJava8StreamApi avgt 10 1706.676 ± 436.867 µs/op
test9_UsingApacheIterableMap avgt 10 3289.866 ± 1445.564 µs/op图表(性能测试取决于地图大小)表(性能测试取决于地图大小) 100 600 1100 1600 2100test10 0.333 1.631 2.752 5.937 8.024test3 0.309 1.971 4.147 8.147 10.473test6 0.372 2.190 4.470 8.322 10.531test1 0.405 2.237 4.616 8.645 10.707test2 0.376 2.267 4.809 8.403 10.910test7 0.473 2.448 5.668 9.790 12.125test9 0.565 2.830 5.952 13.220 16.965test4 0.808 5.012 8.813 13.939 17.407test5 0.810 5.104 8.533 14.064 17.422test8 5.173 12.499 17.351 24.671 30.403所有测试都在GitHub上。
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RISEBY
在Java 8中,您可以使用新的lambdas功能清洁和快速地执行此操作: Map<String,String> map = new HashMap<>();
map.put("SomeKey", "SomeValue");
map.forEach( (k,v) -> [do something with key and value] );
// such as
map.forEach( (k,v) -> System.out.println("Key: " + k + ": Value: " + v));类型k和v将由编译器推断,不再需要使用Map.Entry。十分简单!