The put method in HashMap is defined like this: Object put(Object key, Object value) key is the first parameter, so in your put, “one” is the key. You can’t easily look up by value in a HashMap, if you really want to do that, it would be a linear search done by calling entrySet(), like … Read more
Have you tried to use the Map method that way: Mapper.Map<DestinationClass, SourceClass>(object to convert) ? With the 2.2 version of AutoMapper, this is how we use it and it works fine for us.
Short answer: you’re doing it right. ReadonlyMap<K, V> is essentially a supertype of Map<K, V> since the methods and properties it does have match up with those of Map<K,V>. So by returning a Map as a ReadonlyMap, all you’re doing is widening the type of the value. By the way, that means you can skip … Read more
If you need to add all the values in a Map, try this: float sum = 0.0f; for (float f : map.values()) { sum += f; } At the end, the sum variable will contain the answer. So yes, for traversing a Map‘s values it’s best to use a for loop.
There is no way to get the count of keys in a bucket without listing all the objects this is a limitation of AWS S3 (see https://forums.aws.amazon.com/thread.jspa?messageID=164220). Getting the Object Summaries (HEAD) doesn’t get the actual data so should be a relatively inexpensive operation and if you are just discarding the list then you could … Read more
When we create a list from an array using java.util.Arrays.asList() , the list is mutable. Yes and no: The list may be modified, by calling list.set(index, element); But the list may not be structurally modified. That means that it is not possible to add elements to the list or remove elements from the list. The … Read more
Filtering is one way to do this, as discussed in other answers. Filtering is not scalable though. On the surface time complexity would appear to be O(n) (i.e. already not scalable if the number of objects in the collection will grow), but actually because one or more tests need to be applied to each object … Read more
For what you need, List<string> is probably the most versatile. StringCollection was handy in 1.1, when (without generics) you needed specific classes for typed collections. Collection<string> is handy if you want to subclass it to provide validation etc. Either way, in 3.5, LINQ will provide lots of additional methods for them – but without LINQ, … Read more
The most obvious difference is that take() can only use elements at the beginning, you can combine it with skip() like list.skip(3).take(5) to get similar behavior though. list.take() is lazy evaluated which works nice with functional style programming and might be more efficient if the elements aren’t actually iterated over later. list.take() also is tolerant … Read more
As per my understanding concurrent collection classes preferred over synchronized collection because concurrent collection classes don’t take lock on complete collection object. Instead it takes lock on small segment of collection object. This is true for some collections but not all. A map returned by Collections.synchronizedMap locks the entire map around every operation, whereas ConcurrentHashMap … Read more