Summary ArrayList with ArrayDeque are preferable in many more use-cases than LinkedList. If you’re not sure — just start with ArrayList. TLDR, in ArrayList accessing an element takes constant time [O(1)] and adding an element takes O(n) time [worst case]. In LinkedList adding an element takes O(n) time and accessing also takes O(n) time but LinkedList … Read more
Difference between Arrays.asList(array) and new ArrayList(Arrays.asList(array)) – Read For Learn Skip to content First, let’s see what this does:Arrays.asList(ia) It takes an array ia and creates a wrapper that implements List<Integer>, which makes the original array available as a list. Nothing is copied and all, only a single wrapper object is created. Operations on the list wrapper are … Read more
Actually, probably the “best” way to initialize the ArrayList is the method you wrote, as it does not need to create a new List in any way: ArrayList<String> list = new ArrayList<String>(); list.add(“A”); list.add(“B”); list.add(“C”); The catch is that there is quite a bit of typing required to refer to that list instance. There are … Read more
How to sort an ArrayList?
They are entirely different constructs. A HashMap is an implementation of Map. A Map maps keys to values. The key look up occurs using the hash. On the other hand, a HashSet is an implementation of Set. A Set is designed to match the mathematical model of a set. A HashSet does use a HashMap to back its implementation, as you noted. However, it implements an entirely different interface. … Read more
List iterators guarantee first and foremost that you get the list’s elements in the internal order of the list (aka. insertion order). More specifically it is in the order you’ve inserted the elements or on how you’ve manipulated the list. Sorting can be seen as a manipulation of the data structure, and there are several ways … Read more
keySet() only returns a set of keys from your hash map, you should iterate this key set and the get the value from the hash map using these keys. In your example, the type of the hash map’s key is TypeKey, but you specified TypeValue in your generic for-loop, so it cannot be compiled. You should change it to: for … Read more
When its comes to the behavior of ArrayList and HashSet they are completely different classes. 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 ensures there … Read more
FIFO based Queue implementations?
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: List<Integer> list = new ArrayList<Integer>(); If your using … Read more
