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Java: Collections Class
Posted on: April 17, 2011 at 12:00 AM
This page discusses - Java: Collections Class

Java Notes

Collections Class

The java.util.Collections class contains static utility methods for manipulating collections.

Some useful Collections methods

Assume the following declarations have been made, where T is a class or interface type.

   int i; 
   List<? extends T> list;
   List<T> listT;
   List<?> listO;
   Comparator<? super T> comp; 
   T key; 
   T t;
   Object obj; 
   Collection<? extends T> coll;
   
ReturnsMethodAction
Rearranging - Sorting, Shuffling, . . .
 sort(listT) Sorts listT. Elements must be Comparable<T>.
Stable, O(N log N).
 sort(listT, comp) Sorts listT using a comparator.
 shuffle(listO) Puts the elements of listO in random order.
 reverse(listO) Reverses the elements of list.
Searching
i =binarySearch(list, key) Searches in list for key. Elements must implement Comparable<T>. Returns index of element or negative value if not found. See Binary Search.
i = binarySearch(list, key, comp) Searches in list for key using Comparator comp. Returns index of element or negative value if not found. See Binary search.
t =max(coll) Returns maximum valued Comparable object in the Collection coll.
t =max(coll, comp) Returns maximum valued object in the Collection coll using Comparator comp.
t =min(coll) Returns minimum valued Comparable object in the Collection coll.
t =min(coll, comp) Returns minimum valued object in the Collection coll using Comparator comp.

There are many more methods in Collections, but the above are a good start.

Copyleft 2006 Fred Swartz MIT License
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