Java.util.Arrays.binarySearch() Method

Description

The java.util.Arrays.binarySearch(T[] a, T key, int fromIndex, int toIndex, Comparator<? super T> c) method searches a range of the specified array for the specified object using the binary search algorithm. The range must be sorted into ascending order according to the specified comparator before making this call. If it is not sorted, the results are undefined.

Declaration

Following is the declaration for java.util.Arrays.binarySearch(super,index) method

public static <T> int binarySearch(T[] a, T key, int fromIndex, int toIndex, Comparator<? super T> c)

Parameters

• a − This is the array to be searched.

• fromIndex − The index of the first element (inclusive) to be searched.

• toIndex-- The index of the last element (exclusive) to be searched.

• key − This is the value to be searched for.

• c − This is the comparator by which the array is ordered. A null value indicates that the elements natural ordering should be used.

Return Value

This method returns index of the search key, if it is contained in the array within the specified range; otherwise, (-(insertion point) - 1). The insertion point is defined as the point at which the key would be inserted into the array: the index of the first element in the range greater than the key, or toIndex if all elements in the range are less than the specified key.

Exception

• ClassCastException − if the range contains elements that are not mutually comparable using the specified comparator, or the search key is not comparable to the elements in the range using this comparator.

• IllegalArgumentException − if fromIndex > toIndex

• ArrayIndexOutOfBoundsException − if fromIndex < 0 or toIndex > a.length

Example

The following example shows the usage of java.util.Arrays.binarySearch(super,index) method.

package com.tutorialspoint;

import java.util.Arrays;
import java.util.Comparator;

public class ArrayDemo {
   
   public static void main(String[] args) {

      // initializing unsorted short array
      Short shortArr[] = new Short[]{5, 2, 15, 52, 10};

      // use comparator as null, sorting as natural ordering
      Comparator<Short> comp = null;

      // sorting array
      Arrays.sort(shortArr, comp);

      // let us print all the elements available in list
      System.out.println("The sorted short array is:");
      for (short number : shortArr) {
         System.out.println("Number = " + number);
      }

      // entering the value to be searched 
      short searchVal = 15;

      // search between index 1 and 4
      int retVal = Arrays.binarySearch(shortArr, 1, 4, searchVal, comp);
      System.out.println("The index of element 15 is : " + retVal);

      // search between index 0 and 3, where searchVal doesn't exist
      retVal = Arrays.binarySearch(shortArr, 0, 3, searchVal, comp);
      System.out.println("The index of element 15 is : " + retVal);
   }
}

Let us compile and run the above program, this will produce the following result −

The sorted short array is:
Number = 2
Number = 5
Number = 10
Number = 15
Number = 52
The index of element 15 is : 3
The index of element 15 is : -4