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
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<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
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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
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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服務器之家網站的支持！
原文鏈接：https://segmentfault.com/a/1190000015421902
