Java Map 通过 key 或者 value 过滤的实例代码

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"));  }}

总结

以上所述是小编给大家介绍的Java Map 通过 key 或者 value 过滤的实例代码，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对武林网网站的支持！