hashmap使用

hashmap作为dao对象存储数据库数据

list是把每一个数据库的字段都映射了，而hashmap则是唯一id:数据库字段作为key

hashmap遍历方式

public class Main {//使用迭代器（Iterator）EntrySetpublic static void main(String[] args) {// 创建并赋值 HashMapMap<Integer, String> map = new HashMap();map.put(1, "Java");map.put(2, "JDK");map.put(3, "Spring Framework");map.put(4, "MyBatis framework");map.put(5, "Java");// 遍历Iterator<Map.Entry<Integer, String>> iterator = map.entrySet().iterator();while (iterator.hasNext()) {Map.Entry<Integer, String> entry = iterator.next();System.out.println(entry.getKey());System.out.println(entry.getValue());}}//ForEach EntrySet@Testpublic void test1(){// 创建并赋值 HashMapMap<Integer, String> map = new HashMap();map.put(1, "Java");map.put(2, "JDK");map.put(3, "Spring Framework");map.put(4, "MyBatis framework");map.put(5, "Java");// 遍历for (Map.Entry<Integer, String> entry : map.entrySet()) {System.out.print(entry.getKey());System.out.print(entry.getValue());}}//ForEach KeySet@Testpublic void test2(){// 创建并赋值 HashMapMap<Integer, String> map = new HashMap();map.put(1, "Java");map.put(2, "JDK");map.put(3, "Spring Framework");map.put(4, "MyBatis framework");map.put(5, "Java");// 遍历for (Integer key : map.keySet()) {System.out.print(key);System.out.print(map.get(key));}}//Lambda@Testpublic void test3(){// 创建并赋值 HashMapMap<Integer, String> map = new HashMap();map.put(1, "Java");map.put(2, "JDK");map.put(3, "Spring Framework");map.put(4, "MyBatis framework");map.put(5, "Java中文社群");// 遍历map.forEach((key, value) -> {System.out.print(key);System.out.print(value);});}//Streams API 单线程@Testpublic void test4(){// 创建并赋值 HashMapMap<Integer, String> map = new HashMap();map.put(1, "Java");map.put(2, "JDK");map.put(3, "Spring Framework");map.put(4, "MyBatis framework");map.put(5, "Java中文社群");// 遍历map.entrySet().parallelStream().forEach((entry) -> {System.out.print(entry.getKey());System.out.print(entry.getValue());});}
}