超牛牪犇Java之Map集合

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于 2018-05-24 21:23:57 发布

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本文链接：https://blog.youkuaiyun.com/EnchantedLLL/article/details/80441195

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一.Map

Map是双列集合

1.是以键值对的形式保存数据的 key value

2.键的值唯一

HashSet和HashMap的关系:

HashSet是依赖Map来存储数据的

Set在保存数据的时候实际上就是向Map中的key这一列中存数据

(HashMap:去重指的是key这列

TreeMap:排序指的是key这列)

Map的一些常见方法:

1.put方法添加

(返回的是被覆盖的之前的value值)

2.判断包含(判断的是key)返回值是布尔类型

containsKey()

3.判断包含value(判断的是value)返回值是布尔类型

containsValue()

4.获取Map中所有Key的Set集合

Set<String> keySet = map.keySet();

5.获取Map中所有Value的collection集合

Collection<Integer> v1 = map.values();

6.删除根据Key删除整个键值对

map.remove(key);

7.HashMap的去重:

和Set集合一样重写HashCode和equals方法去重

8.遍历Map

HashMap<String, Integer> map = new HashMap<>();
	map.put("大娃", 10);
	map.put("二娃", 11);
	map.put("三娃", 12);
	map.put("四娃", 13);
	Set<String> keySet = map.keySet();
	for (String string : keySet) {
		Integer integer = map.get(string);
		System.out.println(string + "=" +integer);
}

9.Entry接口

Entry接口是Map接口中的内部接口

Entry中保存的是键值对对象相当于把map中的key和value封装成了一个对象

HashMap<String, Integer> map = new HashMap<>();
		map.put("大娃", 10);
		map.put("二娃", 11);
		map.put("三娃", 12);
		map.put("四娃", 13);
		//利用entrySet遍历集合(迭代器/增强for循环)
		Set<Entry<String, Integer>> entrySet = map.entrySet();
		//迭代器
		Iterator<Entry<String, Integer>> iterator = entrySet.iterator();
		while (iterator.hasNext()) {
			Entry<String, Integer> next = iterator.next();
			System.out.println(next);
		}
		//增强for循环
		for (Entry<String, Integer> entry : entrySet) {
			String key = entry.getKey();
			Integer value = entry.getValue();
			System.out.println(key + "=" + value);
		}
	}

二.Collections类

collections类是集合的工具类

方法:

1.随机打乱集合顺序:(相当于洗牌)

Collections.shuffle(list);

2.反转

Collections.reverse(list);

3.排序

Collections.sort(list);

4.二分查找

int binarySearch = Collections.binarySearch(list, 20);

example:

模拟斗地主(用Map集合)

1.洗牌

2.发牌

3.看牌

public static void main(String[] args) {
	String[] s1 = {"3","4","5","6","7","8","9","10","J","Q","K","A","2"};
	String[] s2 = {"♠️","♥️","♣️","♦️"};
	HashMap<Integer, String> hashMap = new HashMap<>();
	int num = 0;
	for (int i = 0; i < s1.length; i++) {
		for (int j = 0; j < s2.length; j++) {
			String str = s2[j] + s1[i];
			hashMap.put(num , str);
			num++;
		}
	}
	hashMap.put(52,"小王");
	hashMap.put(53,"大王");
	System.out.println(hashMap);
	ArrayList<Integer> arrayList = new ArrayList<>();
	for (int i = 0; i < hashMap.size(); i++) {
		arrayList.add(i);
	}
	Collections.shuffle(arrayList);
	System.out.println(arrayList);
	TreeSet<Integer> treeSet1 = new TreeSet<>();
	TreeSet<Integer> treeSet2 = new TreeSet<>();
	TreeSet<Integer> treeSet3 = new TreeSet<>();
	TreeSet<Integer> treeSet4 = new TreeSet<>();
	for (int i = 0; i < arrayList.size(); i++) {
		int pai = arrayList.get(i);
		if (i >= arrayList.size() - 3) {
			treeSet4.add(pai);
		}
		if (i % 3 == 0 && i < arrayList.size() - 3) {
			treeSet1.add(pai);
		}
		if (i % 3 == 1 && i < arrayList.size() - 3) {
			treeSet2.add(pai);
		}
		if (i % 3 == 2 && i < arrayList.size() - 3) {
			treeSet3.add(pai);
		}
	}
	System.out.println(treeSet1);
	System.out.println(treeSet2);
	System.out.println(treeSet3);
	System.out.println(treeSet4);
	kanPai(hashMap, treeSet1);		
	kanPai(hashMap, treeSet2);
	kanPai(hashMap, treeSet3);
	kanPai(hashMap, treeSet4);	
}
//看牌的方法
private static void kanPai(HashMap<Integer, String> map,TreeSet<Integer> set) {
	for (Integer integer : set) {
		String string = map.get(integer);		
		System.out.print(string + "  ");
	}
	System.out.println();
}