import org.junit.Test; import java.util.*; /** * @ Description:Map接口常用方法（以HashMap为例） * 常用方法（HashMap为例） *

* 增：`put(Object key,Object value)` *

* 删：`remove(Object key)` *

* 改;`put(Object key,Object value)` *

* 查:`get(Object key)` *

* 长度:`size()` *

* 遍历:`keySet(), values(), entrySet()` * @ Author: Jay * @ Date: Create in 11:05 2021/4/15 * @ Version: */ public class MapTest { @Test public void MapTest1() { Map map = new HashMap();//没要求泛型时，不要求key类型相同 //put() map.put("AA", 1); map.put("BB", 2); map.put("CC", 1); map.put("ab", 21); map.put("AA", 110);//如果key存在，则修改 System.out.println(map); Map map1 = new HashMap(); map1.put("DD", 45); map1.put("EE", 43); //putAll(map) map1.putAll(map); System.out.println(map1); //remove(key),返回删除元素的value Object value = map1.remove("DD"); System.out.println(value); //clear() map.clear();//map = null,但还在 System.out.println(map.size());//0 System.out.println(map);//{} //isEmpty() System.out.println(map.isEmpty()); //查询 //get(key) System.out.println(map1.get("AA")); System.out.println(map1.get("MM"));//不存在返回：null //containsKey(key) System.out.println(map1.containsKey("AA")); //containsValue(value) System.out.println(map1.containsValue(1)); //size() System.out.println("size:" + map1.size()); //equals() } //遍历（掌握） @Test public void MapTest2() { Map map = new HashMap(); map.put("AA", 1); map.put("BB", 2); map.put("CC", 3); map.put("ab", 4); //遍历所有key集合：keySet() Set set = map.keySet(); Iterator iterator = set.iterator(); while (iterator.hasNext()) System.out.println(iterator.next()); //遍历所有的Values Collection values = map.values(); for (Object obj : values) { System.out.println(obj); } //遍历所有key-value //方式一：entrySet() Set entrySet = map.entrySet(); Iterator iterator1 = entrySet.iterator(); while (iterator1.hasNext()) { //System.out.println(iterator1.next());//直接输出Node Object obj = iterator1.next(); //entrySet集合长得元素都是entry Map.Entry entry = (Map.Entry) obj; System.out.println(entry.getKey() + "-->" + entry.getValue()); } //方式二：分别取 Set keyset = map.keySet(); Iterator iterator2 = keyset.iterator(); while (iterator2.hasNext()) { Object key = iterator2.next(); Object value = map.get(key); System.out.println(key + "--->" + value); } } }