JAVA-HashMap基础API

import java.util.*;
import java.util.ArrayList;

public class HashMapTest {
    public static void main(String[] args) {
        HashMap<String, ArrayList<String>> map = new HashMap<>();

        String group1Leader = "yxc";
        ArrayList<String> list1 = new ArrayList<>();
        list1.add(group1Leader);
        list1.add("java");
        list1.add("python");
        list1.add("cpp");
        list1.add("js");
        map.put(group1Leader,list1);

        String group2Leader = "wyf";
        ArrayList<String> list2 = new ArrayList<>();
        list2.add(group2Leader);
        list2.add("hadoop");
        list2.add("hive");
        list2.add("spark");
        list2.add("flink");
        map.put(group2Leader,list2);

        Set<Map.Entry<String, ArrayList<String>>> entries = map.entrySet();
        for (Map.Entry<String, ArrayList<String>> entry : entries) {
            String key = entry.getKey();
            ArrayList<String> value = entry.getValue();
            System.out.println("组长：" + key);
            System.out.println("组员有：");
            for (String name : value) {
                System.out.println("\t" + name);
            }
        }

        System.out.println("----------------");

        Collection<ArrayList<String>> values = map.values();
        ArrayList<Object> all = new ArrayList<>();
        for (ArrayList<String> group : values) {
            all.addAll(group);
        }
        System.out.println(all.contains("flink"));

        System.out.println("----------------");
        /* Hashtable: 线程安全，不允许 key，value 为 null
           HashMap  : 线程不安全  允许 key, value 为 null
           LinkedHashMap: 遍历时体现添加顺序
           TreeMap:    红黑树
                       可以按照key大小排序，key类型必须实现Comparable接口
                       或者在创建Treemap的时候指定为Comparator的实现类

          StringBuilder     StringBuffer
           Vector            ArrayList
           Hashtable         HashMap


           读JDBC中的 File 配置文件(jdbc.properties)
           使用类加载器和jdbc建立通道        load加载数据
           InputStream in = classLoader.getResourceAsStream(jdbc.properties)
        */
    }
}