java中实现list或set转map的方法

List<String> stringList = Lists.newArrayList("t1", "t2", "t3"); Map<String, String> map = Maps.newHashMapWithExpectedSize(stringList.size()); for (String str : stringList) {   map.put(str, str); } 

/** * Returns an immutable map for which the {@link Map#values} are the given  * elements in the given order, and each key is the product of invoking a  * supplied function on its corresponding value.  *  * @param values the values to use when constructing the {@code Map}  * @param keyFunction the function used to produce the key for each value  * @return a map mapping the result of evaluating the function {@code  *     keyFunction} on each value in the input collection to that value  * @throws IllegalArgumentException if {@code keyFunction} produces the same  *     key for more than one value in the input collection  * @throws NullPointerException if any elements of {@code values} is null, or  *     if {@code keyFunction} produces {@code null} for any value  */ public static <K, V> ImmutableMap<K, V> uniqueIndex(   Iterable<V> values, Function<? super V, K> keyFunction) {  return uniqueIndex(values.iterator(), keyFunction); }  /**  * Returns an immutable map for which the {@link Map#values} are the given  * elements in the given order, and each key is the product of invoking a  * supplied function on its corresponding value.  *  * @param values the values to use when constructing the {@code Map}  * @param keyFunction the function used to produce the key for each value  * @return a map mapping the result of evaluating the function {@code  *     keyFunction} on each value in the input collection to that value  * @throws IllegalArgumentException if {@code keyFunction} produces the same  *     key for more than one value in the input collection  * @throws NullPointerException if any elements of {@code values} is null, or  *     if {@code keyFunction} produces {@code null} for any value  * @since 10.0  */ public static <K, V> ImmutableMap<K, V> uniqueIndex(   Iterator<V> values, Function<? super V, K> keyFunction) {  checkNotNull(keyFunction);  ImmutableMap.Builder<K, V> builder = ImmutableMap.builder();  while (values.hasNext()) {   V value = values.next();   builder.put(keyFunction.apply(value), value);  }  return builder.build(); } 

List<String> stringList = Lists.newArrayList("t1", "t2", "t3"); Map<String, String> map = Maps.uniqueIndex(stringList, new Function<String, String>() {   @Override   public String apply(String input) {     return input;   } }); 

@Test  public void convert_list_to_map_with_java8_lambda () {        List<Movie> movies = new ArrayList<Movie>();    movies.add(new Movie(1, "The Shawshank Redemption"));    movies.add(new Movie(2, "The Godfather"));      Map<Integer, Movie> mappedMovies = movies.stream().collect(        Collectors.toMap(Movie::getRank, (p) -> p));      logger.info(mappedMovies);      assertTrue(mappedMovies.size() == 2);    assertEquals("The Shawshank Redemption", mappedMovies.get(1).getDescription());  }