Which algorithm is used by collections sort

This method provides interoperability between legacy APIs that return enumerations and new APIs that require collections. Parameters: e - enumeration providing elements for the returned array list Returns: an array list containing the elements returned by the specified enumeration.

Parameters: c - the collection in which to determine the frequency of o o - the object whose frequency is to be determined Throws: NullPointerException - if c is null Since: 1. Care must be exercised if this method is used on collections that do not comply with the general contract for Collection.

Implementations may elect to iterate over either collection and test for containment in the other collection or to perform any equivalent computation. If either collection uses a nonstandard equality test as does a SortedSet whose ordering is not compatible with equals , or the key set of an IdentityHashMap , both collections must use the same nonstandard equality test, or the result of this method is undefined.

Care must also be exercised when using collections that have restrictions on the elements that they may contain.

Collection implementations are allowed to throw exceptions for any operation involving elements they deem ineligible. For absolute safety the specified collections should contain only elements which are eligible elements for both collections.

Note that it is permissible to pass the same collection in both parameters, in which case the method will return true if and only if the collection is empty. Parameters: c1 - a collection c2 - a collection Returns: true if the two specified collections have no elements in common. Throws: NullPointerException - if either collection is null. NullPointerException - if one collection contains a null element and null is not an eligible element for the other collection.

Elements to be added may be specified individually or as an array. The behavior of this convenience method is identical to that of c. When elements are specified individually, this method provides a convenient way to add a few elements to an existing collection: Collections.

The resulting set displays the same ordering, concurrency, and performance characteristics as the backing map. In essence, this factory method provides a Set implementation corresponding to any Map implementation. There is no need to use this method on a Map implementation that already has a corresponding Set implementation such as HashMap or TreeMap.

Each method invocation on the set returned by this method results in exactly one method invocation on the backing map or its keySet view, with one exception. The addAll method is implemented as a sequence of put invocations on the backing map.

The specified map must be empty at the time this method is invoked, and should not be accessed directly after this method returns. Method add is mapped to push , remove is mapped to pop and so on. This view can be useful when you would like to use a method requiring a Queue but you need Lifo ordering. Each method invocation on the queue returned by this method results in exactly one method invocation on the backing deque, with one exception. The addAll method is implemented as a sequence of addFirst invocations on the backing deque.

Parameters: deque - the deque Returns: the queue Since: 1. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.

Object java. Collections public class Collections extends Object This class consists exclusively of static methods that operate on or return collections. It contains polymorphic algorithms that operate on collections, "wrappers", which return a new collection backed by a specified collection, and a few other odds and ends. Returns a view of a Deque as a Last-in-first-out Lifo Queue. Searches the specified list for the specified object using the binary search algorithm.

Returns true if the two specified collections have no elements in common. Returns the number of elements in the specified collection equal to the specified object. Returns the starting position of the first occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence.

Returns the starting position of the last occurrence of the specified target list within the specified source list, or -1 if there is no such occurrence. Returns an array list containing the elements returned by the specified enumeration in the order they are returned by the enumeration. Returns the maximum element of the given collection, according to the natural ordering of its elements.

Returns the maximum element of the given collection, according to the order induced by the specified comparator. Returns the minimum element of the given collection, according to the natural ordering of its elements. Returns the minimum element of the given collection, according to the order induced by the specified comparator.

Returns an immutable list consisting of n copies of the specified object. Returns a comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface. Returns a comparator that imposes the reverse ordering of the specified comparator.

Returns an immutable map, mapping only the specified key to the specified value. Sorts the specified list into ascending order, according to the natural ordering of its elements. Sorts the specified list according to the order induced by the specified comparator.

Returns a synchronized thread-safe collection backed by the specified collection. Returns a synchronized thread-safe sorted map backed by the specified sorted map. Returns a synchronized thread-safe sorted set backed by the specified sorted set. Reverses the order of the elements in the specified list. Randomly permutes the specified list using a default source of randomness. Randomly permute the specified list using the specified source of randomness. Swaps the elements at the specified positions in the specified list.

Replaces all of the elements of the specified list with the specified element. Copies all of the elements from one list into another.

Rotates the elements in the specified list by the specified distance. Replaces all occurrences of one specified value in a list with another. Returns an unmodifiable view of the specified collection.

Returns an unmodifiable view of the specified set. Returns an unmodifiable view of the specified sorted set. Returns an unmodifiable view of the specified list. Returns an unmodifiable view of the specified map. Returns an unmodifiable view of the specified sorted map. Returns a synchronized thread-safe set backed by the specified set. Returns a synchronized thread-safe list backed by the specified list.

Returns a synchronized thread-safe map backed by the specified map. Returns a dynamically typesafe view of the specified collection. Returns a dynamically typesafe view of the specified set. Returns a dynamically typesafe view of the specified sorted set. Returns a dynamically typesafe view of the specified list. Returns a dynamically typesafe view of the specified map.

Thereof, how do you sort collections? Java Collections. If we want to sort the elements in reverse order we could use following methods: reverseOrder : Returns a Comparator that imposes the reverse of natural ordering of elements of the collection. Secondly, how do you use collections sort in ArrayList? Arrays uses Two Sorting Algorithms. Arrays uses quicksort actually dual pivot quicksort in the most recent version for primitive types such as int and mergesort for objects that implement Comparable or use a Comparator.

So, in the end, Collections sort uses Arrays sort of object elements behind the scenes. This implementation uses merge sort or tim sort.

According to the Javadoc, only primitive arrays are sorted using Quicksort. Object arrays are sorted with a Mergesort as well. When would you use collections sort? We can use Collections. What is the difference between arrays sort and collections sort? How do you sort a list? The algorithm used by java. In its day it was written in by Joshua Bloch , it was a fine choice, but today but we can do much better. It is a stable, adaptive, iterative mergesort that requires far fewer than n log n comparisons when running on partially sorted arrays, while offering performance comparable to a traditional mergesort when run on random arrays.

Like all proper mergesorts timsort is stable and runs in O n log n time worst case. Contrast this with the current implementation, which always requires extra space for n object references, and beats n log n only on nearly sorted lists. Joshua Bloch ported it from C to Java and end tested, benchmarked, and tuned the resulting code extensively. The resulting code is a drop-in replacement for java. Additionally, a heap must be almost complete. An almost complete binary tree of depth d has a subtree of depth d-1 with the same root that is complete, and in which each node with a left descendent has a complete left subtree.

In other words, when adding a node, we always go for the leftmost position in the highest incomplete level. If the heap is a max-heap , then all of the children are smaller than the parent, and if it's a min-heap all of them are larger.

In other words, as you move down the tree, you get to smaller and smaller numbers min-heap or greater and greater numbers max-heap. Here's an example of a max-heap:. You can envision it as reading from the graph level by level, left to right. You can check this for yourself. Knowing this, you can easily "max-heapify" any given array. For each element, check if any of its children are smaller than it. If they are, swap one of them with the parent, and recursively repeat this step with the parent because the new large element might still be bigger than its other child.

We recursively heapify for 5 now. Once we've learned to heapify an array the rest is pretty simple. We swap the root of the heap with the end of the array, and shorten the array by one. When we look at the heapify function, everything seems to be done in O 1 , but then there's that pesky recursive call. How many times will that be called, in the worst case scenario?

Well, worst-case, it will propagate all the way to the top of the heap. Because heapSort is clearly O n due to for-loops iterating through the entire array, this would make the total complexity of Heapsort O nlog n.

Heapsort is an in-place sort, meaning it takes O 1 additional space, as opposed to Merge Sort, but it has some drawbacks as well, such as being difficult to parallelize. Quicksort is another Divide and Conquer algorithm. It picks one element of an array as the pivot and sorts all of the other elements around it, for example smaller elements to the left, and larger to the right.

This guarantees that the pivot is in its proper place after the process. Then the algorithm recursively does the same for the left and right portions of the array. The worst case scenario is when the biggest or smallest element is always picked for pivot. The equation would then look like this:. This may sound bad, as we have already learned multiple algorithms which run in O nlog n time as their worst case, but Quicksort is actually very widely used.

This is because it has a really good average runtime, also bounded by O nlog n , and is very efficient for a large portion of possible inputs. One of the reasons it is preferred to Merge Sort is that it doesn't take any extra space, all of the sorting is done in-place, and there's no expensive allocation and deallocation calls. That all being said, it's often useful to run all of these algorithms on your machine a few times to get an idea of how they perform.

They'll perform differently with different collections that are being sorted of course, but even with that in mind, you should be able to notice some trends. Let's run all of the implementations, one by one, each on a copy of a shuffled array of 10, integers:. We can evidently see that Bubble Sort is the worst when it comes to performance.