Java 如何验证HashMap中的值是否存在

How to verify if a value in HashMap exist

提问by Luis Lavieri

I have the following HashMapwhere the keyis a Stringand the valueis represented by an ArrayList:

我有以下内容HashMap，其中keyis aString和 thevalue由 an 表示ArrayList：

 HashMap<String, ArrayList<String>> productsMap = AsyncUpload.getFoodMap();

I also have another ArrayList<String> foodsimplemented in my application.

ArrayList<String> foods我的应用程序中还有另一个实现。

My question is, What would be the best way to find out if my HashMapcontains a Specific Stringfrom my second ArrayList?

我的问题是，从我的第二个中找出我是否HashMap包含一个特定的最好方法是什么？StringArrayList

I have tried without success:

我试过没有成功：

Iterator<String> keySetIterator = productsMap.keySet().iterator();
Iterator<ArrayList<String>> valueSetIterator = productsMap.values().iterator();

    while(keySetIterator.hasNext() && valueSetIterator.hasNext()){
        String key = keySetIterator.next();
        if(mArrayList.contains(key)){
            System.out.println("Yes! its a " + key);
        }
    }

采纳答案by Mena

Why not:

为什么不：

// fast-enumerating map's values
for (ArrayList<String> value: productsMap.values()) {
    // using ArrayList#contains
    System.out.println(value.contains("myString"));
}

And if you have to iterate over the whole ArrayList<String>, instead of looking for one specific value only:

如果您必须遍历整个ArrayList<String>，而不是仅查找一个特定值：

// fast-enumerating food's values ("food" is an ArrayList<String>)
for (String item: foods) {
    // fast-enumerating map's values
    for (ArrayList<String> value: productsMap.values()) {
        // using ArrayList#contains
        System.out.println(value.contains(item));
    }
}

Edit

编辑

Past time I updated this with some Java 8 idioms.

过去我用一些 Java 8 习语更新了这个。

The Java 8 streams API allows a more declarative (and arguably elegant) way of handling these types of iteration.

Java 8 流 API 允许以更具声明性（并且可以说是优雅）的方式来处理这些类型的迭代。

For instance, here's a (slightly too verbose) way to achieve the same:

例如，这是实现相同目标的（有点过于冗长）方法：

// iterate foods 
foods
    .stream()
    // matches any occurrence of...
    .anyMatch(
        // ... any list matching any occurrence of...
        (s) -> productsMap.values().stream().anyMatch(
            // ... the list containing the iterated item from foods
            (l) -> l.contains(s)
        )
    )

... and here's a simpler way to achieve the same, initially iterating the productsMapvalues instead of the contents of foods:

...这是实现相同目标的更简单方法，最初迭代productsMap值而不是内容foods：

// iterate productsMap values
productsMap
    .values()
    .stream()
    // flattening to all list elements
    .flatMap(List::stream)
    // matching any occurrence of...
    .anyMatch(
        // ... an element contained in foods
        (s) -> foods.contains(s)
    )

回答by BlackHatSamurai

You need to use the containsKey()method. To do this, you simply get the hashMap you want the key out of, then use the containsKeymethod, which will return a booleanvalue if it does. This will search the whole hashMap without having to iterate over each item. If you do have the key, then you can simply retrieve the value.

您需要使用该containsKey()方法。要做到这一点，您只需获取您想要的键的 hashMap，然后使用该containsKey方法，boolean如果它返回一个值。这将搜索整个 hashMap 而不必遍历每个项目。如果您确实有密钥，那么您可以简单地检索该值。

It might look something like:

它可能看起来像：

if(productsMap.values().containsKey("myKey"))
{
    // do something if hashMap has key
}

Here is the link to Android

这是安卓的链接

From the Android docs:

从 Android 文档：

public boolean containsKey (Object key) Added in API level 1

Returns whether this map contains the specified key. Parameters key the key to search for. Returns

true if this map contains the specified key, false otherwise.

public boolean containsKey（对象键）在 API 级别 1 中添加

返回此映射是否包含指定的键。参数 key 要搜索的键。退货

true if this map contains the specified key, false otherwise.

回答by boxed__l

Try this

尝试这个

Iterator<String> keySetIterator = productsMap.keySet().iterator();
Iterator<ArrayList<String>> valueSetIterator = productsMap.values().iterator();

    while(keySetIterator.hasNext()){
        String key = keySetIterator.next();
        if(valueSetIterator.next().contains(key)){    // corrected here
            System.out.println("Yes! its a " + key);
        }
}

回答by Josh M

If you want the Java 8 way of doing it, you could do something like this:

如果你想要 Java 8 的方式，你可以这样做：

    private static boolean containsValue(final Map<String, ArrayList<String>> map, final String value){
    return map.values().stream().filter(list -> list.contains(value)).findFirst().orElse(null) != null;
}

Or something like this:

或者像这样：

    private static boolean containsValue(final Map<String, ArrayList<String>> map, final String value){
    return map.values().stream().filter(list -> list.contains(value)).findFirst().isPresent();
}

Both should produce pretty much the same result.

两者应该产生几乎相同的结果。

回答by Bastien Aracil

Try this :

尝试这个 ：

public boolean anyKeyInMap(Map<String, ArrayList<String>> productsMap, List<String> keys) {
    Set<String> keySet = new HashSet<>(keys);

    for (ArrayList<String> strings : productsMap.values()) {
        for (String string : strings) {
            if (keySet.contains(string)) {
                return true;
            }
        }
    }

    return false;
}

回答by Sajal Dutta

Here's a sample method that tests for both scenarios. Searching for items in map's keys and also search for items in the lists of each map entry:

这是测试这两种情况的示例方法。在地图的键中搜索项目，并在每个地图条目的列表中搜索项目：

private static void testMapSearch(){

    final ArrayList<String> fruitsList = new ArrayList<String>();        
    fruitsList.addAll(Arrays.asList("Apple", "Banana", "Grapes"));

    final ArrayList<String> veggiesList = new ArrayList<String>();        
    veggiesList.addAll(Arrays.asList("Potato", "Squash", "Beans"));

    final Map<String, ArrayList<String>> productsMap = new HashMap<String, ArrayList<String>>();

    productsMap.put("fruits", fruitsList);
    productsMap.put("veggies", veggiesList);

    final ArrayList<String> foodList = new ArrayList<String>();        
    foodList.addAll(Arrays.asList("Apple", "Squash", "fruits"));

    // Check if items from foodList exist in the keyset of productsMap

    for(String item : foodList){
        if(productsMap.containsKey(item)){
            System.out.println("productsMap contains a key named " + item);
        } else {
            System.out.println("productsMap doesn't contain a key named " + item);
        }
    }

    // Check if items from foodList exits in productsMap's values

    for (Map.Entry<String, ArrayList<String>> entry : productsMap.entrySet()){

        System.out.println("\nSearching on list values for key " + entry.getKey() + "..");

        for(String item : foodList){
            if(entry.getValue().contains(item)){
                System.out.println("productMap's list under key " + entry.getKey() + " contains item " + item);
            } else {
                System.out.println("productMap's list under key " + entry.getKey() + " doesn't contain item " + item);
            }
        }      
    } 
}

Here's the result:

结果如下：

productsMap doesn't contain a key named Apple

productsMap doesn't contain a key named Squash

productsMap contains a key named fruits

Searching on list values for key fruits..

productMap's list under key fruits contains item Apple

productMap's list under key fruits doesn't contain item Squash

productMap's list under key fruits doesn't contain item fruits

Searching on list values for key veggies..

productMap's list under key veggies doesn't contain item Apple

productMap's list under key veggies contains item Squash

productMap's list under key veggies doesn't contain item fruits

productsMap 不包含名为 Apple 的键

productsMap 不包含名为 Squash 的键

productsMap 包含一个名为fruits的键

搜索关键水果的列表值..

主要水果下的 productMap 列表包含项目 Apple

主要水果下的 productMap 列表不包含项目 Squash

关键水果下productMap的列表不包含项目水果

搜索关键蔬菜的列表值..

关键蔬菜下的 productMap 列表不包含 Apple 项

关键蔬菜下的 productMap 列表包含项目 Squash

productMap 在关键蔬菜下的列表不包含项目水果

回答by Tim

hashMap.containsValue("your value");

Will check if the HashMap contains the value

将检查 HashMap 是否包含该值