前言：
眼前同学们对“java的map”都比较关心，咱们都需要学习一些“java的map”的相关知识。那么小编在网上汇集了一些对于“java的map””的相关资讯，希望小伙伴们能喜欢，兄弟们快快来学习一下吧！1.声明及初始化Map1.1 先定义,后赋值
Map<String , Object> map = new HashMap<String , Object>();map.put("key1", "value1");map.put("key2", "value2");map.put("keyN", "valueN");1.2 双括号初始化法Map<String , String> map = new HashMap<String , Object>(){{ put("key1", "value1"); put("key2", "value2"); put("keyN", "valueN");}};1.3 使用初始块public class MyMap { Map<String,String> maps; // 使用初始块定义 { maps = new HashMap<>(); maps.put("key1","value1"); maps.put("key2","value2"); maps.put("key3","value3"); } public void printMap(){ System.out.println(maps); // 输出:{key1=value1, key2=value2, key3=value3} }}2.遍历Map2.1 key=>valueMap<Integer, Integer> map = new HashMap<Integer, Integer>(); for (Map.Entry<Integer, Integer> entry : map.entrySet()) { System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue()); }2.2 遍历keys或valuesMap<Integer, Integer> map = new HashMap<Integer, Integer>(); //遍历map中的键 for (Integer key : map.keySet()) { System.out.println("Key = " + key); } //遍历map中的值 for (Integer value : map.values()) { System.out.println("Value = " + value); }2.3 使用Iterator遍历2.3.1 使用泛型Map<Integer, Integer> map = new HashMap<Integer, Integer>(); Iterator<Map.Entry<Integer, Integer>> entries = map.entrySet().iterator(); while (entries.hasNext()) { Map.Entry<Integer, Integer> entry = entries.next(); System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue()); }// 在keySet上Iterator<String> iterator = map.keySet().iterator();while (iterator.hasNext()) { String key = iterator.next(); System.out.println("MyClass.testMap key=" + key);}//在values上Iterator<Integer> iterator2 = map.values().iterator();while (iterator2.hasNext()){ Integer values = iterator2.next(); System.out.println("MyClass.testMap values="+values);}2.3.2 不使用泛型Map map = new HashMap(); Iterator entries = map.entrySet().iterator(); while (entries.hasNext()) { Map.Entry entry = (Map.Entry) entries.next(); Integer key = (Integer)entry.getKey(); Integer value = (Integer)entry.getValue(); System.out.println("Key = " + key + ", Value = " + value); }2.4 通过键找值遍历（效率低）Map<Integer, Integer> map = new HashMap<Integer, Integer>(); for (Integer key : map.keySet()) { Integer value = map.get(key); System.out.println("Key = " + key + ", Value = " + value);}3.map接口方法使用3.1 void clear():删除该Map对象中的所有key-value对clear():删除该Map对象中的所有key-value对
Map<String,String> maps = new HashMap<>();maps.put("key1","value1");maps.put("key2","value2");System.out.println("clear前:" + maps); maps.clear();System.out.println("clear后:" + maps);/*** 输出: clear前:{key1=value1, key2=value2} clear后:{}*/3.2 boolean containsKey(Object key)containsKey(Object key):查询Map中是否包含指定的key，如果包含则返回true
Map<String,String> maps = new HashMap<>();maps.put("key1","value1");maps.put("key2","value2");System.out.println("判断key1是否存在:" + maps.containsKey("key1"));System.out.println("判断key8是否存在:" + maps.containsKey("key8"));/*** 输出:判断key1是否存在:true判断key8是否存在:false*/3.3 boolean containsValue(Object value)查询Map中是否包含一个或多个value，如果包含则返回true。
Map<String,String> maps = new HashMap<>();maps.put("key1","value1");maps.put("key2","value2");System.out.println("判断value1是否存在:" + maps.containsValue("value1"));System.out.println("判断value8是否存在:" + maps.containsValue("value8"));/*** 输出:判断value1是否存在:true判断value8是否存在:false*/3.4 Set entrySet()Set entrySet():返回Map中包含的key-value对所组成的Set集合，每个集合元素都是Map.Entry （Entry是Map的内部类）对象。
Map<Integer, Integer> map = new HashMap<Integer, Integer>(); for (Map.Entry<Integer, Integer> entry : map.entrySet()) { System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue()); }3.5 Object get(Object key)返回指定key所对应的value；如果此Map中不包含该key，则返回null。
Map<String,String> maps = new HashMap<>();maps.put("key1","value1");maps.put("key2","value2");System.out.println("key1的值:" + maps.get("key1"));System.out.println("key2的值:" + maps.get("key2"));/*** 输出:key1的值:value1key2的值:value2*/3.6 boolean isEmpty()查询该Map是否为空（即不包含任何key-value对），如果为空则返回true。
Map<String,String> map1 = new HashMap<>();map1.put("key1","value1");map1.put("key2","value2");Map<String,String> map2 = new HashMap<>();System.out.println("map1是否为空:" + map1.isEmpty());System.out.println("map2是否为空:" + map2.isEmpty());/*** 输出:map1是否为空:falsemap2是否为空:true*/3.7 Set keySet()返回该Map中所有key组成的Set集合。
Map<String,String> map1 = new HashMap<>();map1.put("key1","value1");map1.put("key2","value2");System.out.println("keySet结果:" + map1.keySet());// 输出:keySet结果:[key1, key2]3.8 Object put(Object key, Object value):添加一个key-value对，如果当前Map中已有一个与该key相等的key-value对，则新的key-value对会覆盖原来的key-value对。
Map<String,String> map1 = new HashMap<>();map1.put("key1","value1");map1.put("key1","value11");System.out.println("keySet结果:" + map1.keySet());//输出:map1结果:{key1=value11, key2=value2}3.9 void putAll(Map m)将指定Map中的key-value对复制到本Map中。
Map<String,String> map1 = new HashMap<>();map1.put("key1","value1");map1.put("key2","value2");Map<String,String> map2 = new HashMap<>();map2.put("a","php");map2.put("key2","java");map1.putAll(map2);System.out.println("map1结果:" + map1);//输出:{key1=value1, key2=java, a=php}3.10 Object remove(Object key)删除指定key所对应的key-value对，返回被删除key所关联的value，如果该key不存在，则返回null。
Map<String,String> map1 = new HashMap<>();map1.put("key1","value1");map1.put("key2","value2");map1.put("key3","value3");map1.remove("key2");System.out.println("map1结果:" + map1);//输出:map1结果:{key1=value1, key3=value3}3.11 int size()返回该Map里的key-value对的个数。
Map<String,String> map1 = new HashMap<>();map1.put("key1","value1");map1.put("key2","value2");map1.put("key3","value3");System.out.println("map1的key-value对的个数:" + map1.size());//输出:map1的key-value对的个数:33.12 Collection values()返回该Map里所有value组成的Collection。
Map<String,String> map1 = new HashMap<>();map1.put("key1","value1");map1.put("key2","value2");map1.put("key3","value3");System.out.println("map1的value集合:" + map1.values());//输出:map1的value集合:[value1, value2, value3] 版权声明：
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标签： #java的map
