I am relatively new to Java, and often find that I need to sort a Map<Key, Value> on the values. Since the values are not unique, I find myself converting the keySet into an array, and sorting that array through array sort with a custom comparator that sorts on the value associated with the key. … Read more
Python 2.7 and 3.2 added the collections.Counter class, which is a dictionary subclass that maps elements to the number of occurrences of the element. This can be used as a multiset. You can do something like this: As well, if you want to check that every element in b is in a: But since you … Read more
From Effective Java, Item #43 – “Return empty arrays or collections, not null” demonstrates returning an empty collection and perhaps even demonstrates using these emptyList(), emptySet(), and emptyMap() methods on the Collections class to get an empty collection that also has the additional benefit of being immutable. From Item #15 “Minimize Mutability”. From Collections-emptySet-Collections-emptyList-Collections Its a type of programming idiom. This is for people that do not … Read more
How about like this: The Collections.reverseOrder() provides a Comparator that would sort the elements in the PriorityQueue in a the oposite order to their natural order in this case.
I’m new to Java and very confused. I have a large dataset of length 4 int[] and I want to count the number of times that each particular combination of 4 integers occurs. This is very similar to counting word frequencies in a document. I want to create a Map<int[], double> that maps each int[] to a running count … Read more
In Java the type of any variable is either a primitive type or a reference type. Generic type arguments must be reference types. Since primitives do not extend Object they cannot be used as generic type arguments for a parametrized type. Instead use the Integer class which is a wrapper for int: If your using Java 7 you can simplify … Read more
Same way as you would in JavaScript. Note that this sets the element to undefined. Better to use the Array.prototype.splice function:
Yeah. Queue LinkedList being the most trivial concrete implementation.
When its comes to the behavior of ArrayList and HashSet they are completely different classes. ArrayList ArrayList Does not validate duplicates. get() is O(1) contains() is O(n) but you have fully control over the order of the entries. get add contains next remove(0) iterator.remove ArrayList O(1) O(1) O(n) O(1) O(1) O(1) Not thread safe and to make it thread safe you have to use Collections.synchronizedList(…) HashSet … Read more