集合知识2,Hashtable,EnumMap

Hashtable演示

package com.hashtable;

import java.util.Hashtable;

// Hashtable演示
public class HashtableTest {
public static void main(String[] args) {
Hashtable<String, String> ht = new Hashtable<>();
ht.put("a", "aaa");
ht.put("b", "bbb");
//ht.put(null, "ddd");
//ht.put("c", null);
System.out.println(ht);
}
}

枚举集合

package com.enums;

import java.util.EnumMap;
import java.util.Iterator;
import java.util.Set;

// 枚举集合
enum Gender{
MAN, WOMEN
}

public class EnumMapTest {
public static void main(String[] args) {
EnumMap<Gender, String> em = new EnumMap<>(Gender.class);
em.put(Gender.MAN, "男");
em.put(Gender.WOMEN, "女");

System.out.println(em);

Set<Gender> keySet = em.keySet();
Iterator<Gender> it = keySet.iterator();
while(it.hasNext()) {
Gender g = it.next();
System.out.println(g.name());
}
}
}

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