Is there a Class(es) in java for Pre-baked sorting Algorithm code?

Question

I was searching for class that implemented algorithms.. i found some code online...

package sun.misc;

public class Sort {

    private static void swap(Object arr[], int i, int j) {
    Object tmp;

    tmp = arr[i];
    arr[i] = arr[j];
    arr[j] = tmp;
    }

    /**
     * quicksort the array of objects.
     *
     * @param arr[] - an array of objects
     * @param left - the start index - from where to begin sorting
     * @param right - the last index.
     * @param comp - an object that implemnts the Compare interface to resolve thecomparison.
     */
    public static void quicksort(Object arr[], int left, int right, Compare comp) {
    int i, last;

    if (left >= right) { /* do nothing if array contains fewer than two */
        return;          /* two elements */
    }
    swap(arr, left, (left+right) / 2);
    last = left;
    for (i = left+1; i <= right; i++) {
        if (comp.doCompare(arr[i], arr[left]) < 0) {
        swap(arr, ++last, i);
        }
    }
    swap(arr, left, last);
    quicksort(arr, left, last-1, comp);
    quicksort(arr, last+1, right, comp);
    }

    public static void quicksort(Object arr[], Compare comp) {
        quicksort(arr, 0, arr.length-1, comp);
    }
}

Now i am wondering if there are some specific classes for the most commonly algorithms like bubble sort / heap sort / binary tree etc in java ... Do you guys have any idea?

I rolled back your edit - questions about the importance of knowing algorithms will get closed as off-topic here. — skaffman
– skaffman, Commented Jan 3, 2012 at 20:34
You changed the subject of your question (title and bold at the bottom) to ask a completely different question after multiple people took the time to answer. If you want to ask a different question I don't think you should be changing content. That being said; that kind of question is likely best asked on programmers programmers.stackexchange.com — Dave
– Dave, Commented Jan 3, 2012 at 20:35

kapex · Accepted Answer · 2012-01-03 20:06:43Z

3

There are two things you need to look into.

Collections#sort method

And the Comparator interface

edited Jan 3, 2012 at 20:06

kapex

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answered Jan 3, 2012 at 20:03

Dave

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Comments

Aasmund Eldhuset · Accepted Answer · 2012-01-03 20:06:23Z

1

Note that the goal of a standard library is to be useful, not theoretically interesting. Therefore, I strongly doubt that there are any standard implementations of bubble sort, insertion sort, or selection sort, as they are too slow to be useful in practice (except as e.g. subalgorithms in quicksort). Collections.sort() is likely either mergesort, heapsort, or randomized quicksort. TreeSet and SortedMap are likely red-black trees. However, the Java standard itself does not specify which algorithms or data structures are to be used; it only specifies certain performance characteristics. Whoever wrote your Java implementation may choose anything that fits the criteria. For instance, TreeSet must support insert, search, and delete operations in O(lg n) time, which probably makes red-black tree the only realistic choice.

answered Jan 3, 2012 at 20:06

Aasmund Eldhuset

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1 Comment

Roger Lindsjö Over a year ago

+1 for explaining why not to expect to find some of the algorithms in a standard library.

Itay Maman · Accepted Answer · 2012-01-03 20:05:01Z

0

java.util.Collections.sort() is a general purposes sorting method. It takes a collection of Comparable elements as an input (ArrayList, LinkedList, etc.) and stable-sorts it.

The sorting algorithm is a modified mergesort

(see: http://docs.oracle.com/javase/6/docs/api/java/util/Collections.html#sort(java.util.List))

answered Jan 3, 2012 at 20:05

Itay Maman

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Comments

user949300 · Accepted Answer · 2012-01-03 20:05:07Z

0

There are two built-in methods of which I'm aware.

Collections.sort() Javadocs here provides a "modified mergesort".

Arrays.sort() uses a "tuned Quicksort". (see Javadocs here for a citation)

answered Jan 3, 2012 at 20:05

user949300

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1 Comment

Voo Over a year ago

And there's timsort since Java7 and quick/mergesort both (?) use SelectionSort as soon as some threshold is reached.

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