今天写根过滤的时候一下子有点愣眼，先是想到用 Java 原生的 map 循环查出来，但是觉得太 low， 后面思考了一下可以用 Java8 的 Lambda，写完了，又发现 Google Guava 有现成的方法，这里一一列出来，供参考使用。
首先提示，如果照搬我的代码的话别忘了引这些依赖
<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"));
}
}如果觉得内容还不错，可以关注一下我哦
期待与你相遇，一同成长前行！
作者：志哥
链接：https://www.jianshu.com/p/8734656e8d8e
來源：简书
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