今天寫根過濾的時候一下子有點愣眼，先是想到用 Java 原生的 map 循環查出來，但是覺得太 low， 后面思考了一下可以用 Java8 的 Lambda，寫完了，又發現 Google Guava 有現成的方法，這里一一列出來，供參考使用。
首先提示，如果照搬我的代碼的話別忘了引這些依賴
<dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> <exclusions> <exclusion> <groupId>org.hamcrest</groupId> <artifactId>hamcrest-core</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.hamcrest</groupId> <artifactId>hamcrest-library</artifactId> <version>1.3</version> <scope>test</scope> </dependency> <dependency> <groupId>com.google.guava</groupId> <artifactId>guava</artifactId> <version>25.1-jre</version> </dependency></dependencies>
filter by key
public class FilterMapByKeyTest { private Map<Integer, String> WEEK = new HashMap<>(); @Before public void setUp () { WEEK.put(1, "Monday"); WEEK.put(2, "Tuesday"); WEEK.put(3, "Wednesday"); WEEK.put(4, "Thursday"); WEEK.put(5, "Friday"); WEEK.put(6, "Saturday"); WEEK.put(7, "Sunday"); } /** * Java 8之前的版本 */ @Test public void filterMapByKey () { Map<Integer, String> map = new HashMap<>(); for (Map.Entry<Integer, String> entry : WEEK.entrySet()) { if (entry.getKey() <= 3) { map.put(entry.getKey(), entry.getValue()); } } assertThat(map.keySet(), contains(1, 2, 3)); } /** * Java 8 Lambda */ @Test public void filterMapByKeyJava8Lambda () { Map<Integer, String> map = WEEK.entrySet().stream().filter(r -> r.getKey() <= 3) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)); assertThat(map.keySet(), contains(1, 2, 3)); } /** * Google Guava */ @Test public void filterMapByKeyGuava () { Map<Integer, String> map = Maps.filterKeys(WEEK, r -> r <= 3); assertThat(map.keySet(), contains(1, 2, 3)); }}filter by value
public class FilterMapByValueTest { private Map<Integer, String> WEEK = new HashMap<>(); @Before public void setUp () { WEEK.put(1, "Monday"); WEEK.put(2, "Tuesday"); WEEK.put(3, "Wednesday"); WEEK.put(4, "Thursday"); WEEK.put(5, "Friday"); WEEK.put(6, "Saturday"); WEEK.put(7, "Sunday"); } /** * Java 8之前的版本 */ @Test public void filterMapByValue () { Map<Integer, String> map = new HashMap<>(); for (Map.Entry<Integer, String> entry : WEEK.entrySet()) { if (entry.getValue().startsWith("S")) { map.put(entry.getKey(), entry.getValue()); } } assertThat(map.values(), contains("Saturday","Sunday")); } /** * Java 8 Lambda */ @Test public void filterMapByValueJava8Lambda () { Map<Integer, String> map = WEEK.entrySet().stream().filter(r -> r.getValue().startsWith("S")) .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)); assertThat(map.values(), contains("Saturday","Sunday")); } /** * Google Guava */ @Test public void filterMapByValueGuava () { Map<Integer, String> map = Maps.filterValues(WEEK, r -> r.startsWith("S")); assertThat(map.values(), contains("Saturday","Sunday")); }}總結
以上所述是小編給大家介紹的Java Map 通過 key 或者 value 過濾的實例代碼，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對VeVb武林網網站的支持！
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