@TestpublicvoidtestGetProductKeys(){Map<String,Integer>productMap=newHashMap<>();productMap.put("productA",150);productMap.put("productB",300);List<String>keys=newArrayList<>(productMap.keySet());assertEquals(Arrays.asList("productA","productB"),keys);} 1. 2. 3. 4. 5. 6. 7. 8....
HashMap的扩容操作是一项很耗时的任务,所以如果能估算Map的容量,最好给它一个默认初始值,避免进行多次扩容。 HashMap的线程是不安全的,多线程环境中推荐是ConcurrentHashMap。 1、实现原理 HashMap是基于hashing的原理,我们使用put(key, value)存储对象到HashMap中,使用get(key)从HashMap中获取对象。 当我们给put(...
1. map的key或value转list Map map = new HashMap<>(); map.put(1, "apple"); map.put(2, "orange"); map.put(3, "pear"); List keys = new ArrayList<>(map.keySet()); List values = new ArrayList<>(map.values()); 1. 2. 3. 4. 5. 6. 7. 上面代码中,我们通过map的keySet()...
"3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A", "2");//定义一个map集合:用来将数字与每一张牌进行对应HashMap<Integer, String> map =newHashMap<Integer, String>();intindex = 0;//加入大小王map.put(...
Map.Entry represents a key-value pair in HashMap. HashMap's entrySet returns a Set view of the mappings contained in the map. A set of keys is retrieved with the keySet method. HashMap extends AbstractMap and implements Map. The Map provides method signatures including get, put, size, or...
Hash table and linked list implementation of theMapinterface, with well-defined encounter order. C#复制 [Android.Runtime.Register("java/util/LinkedHashMap", DoNotGenerateAcw=true)] [Java.Interop.JavaTypeParameters(new System.String[] {"K","V"})]publicclassLinkedHashMap:Java.Util.HashMap,IDis...
Class HashMap<K,V> Type Parameters: K- the type of keys maintained by this map V- the type of mapped values All Implemented Interfaces: Serializable,Cloneable,Map<K,V> Direct Known Subclasses: LinkedHashMap,PrinterStateReasons public classHashMap<K,V>extendsAbstractMap<K,V> implementsMap<K,...
extends U> valueMapper // Value 映射器 ) { return toMap(keyMapper, valueMapper, throwingMerger(), HashMap::new); } public static <T, K, U, M extends Map<K, U>> Collector<T, ?, M> toMap( Function<? super T, ? extends K> keyMapper, Function<? super T, ? extends U> valueMap...
常用的Map实现包括HashMap(无序)、TreeMap(有序)和LinkedHashMap(保持插入顺序)。 1. foreach 循环遍历 使用entrySet()遍历 Map 是一种常见的方法,可以同时获取键和值: for (Map.Entry<String, String> entry : map.entrySet()) { System.out.println("Key = " + entry.getKey() + ", " + "Value...
没错,Multiset 占据了 List 和 Set 之间的一个灰色地带:允许重复,但是不保证顺序。 举个例子,使用 JDK 如果我们想:“统计每个单词出现的次数” 一般这样写: Map<String, Integer> counts = new HashMap<String, Integer>(); for (String word : words) { Integer count = counts.get(word); if (count ...