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
java
public class Main {
//使用迭代器（Iterator）EntrySet
public static void main(String[] args) {
// 创建并赋值 HashMap
Map<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
@Test
public void test1(){
// 创建并赋值 HashMap
Map<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
@Test
public void test2(){
// 创建并赋值 HashMap
Map<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
@Test
public void test3(){
// 创建并赋值 HashMap
Map<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
@Test
public void test4(){
// 创建并赋值 HashMap
Map<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());
});
}
}