java.util.Arrays binarySearch()


On this document we will be showing a java example on how to use the binarySearch() method of Arrays Class. This method is overloaded in such a way that all possible data type is handled. Basically the binarySearch() method is used to searches the specified array for the specified value using the binary search algorithm. Make a note that the array must be sorted (as by the sort(arr[]) method) prior to making this call. If it is not sorted, the results are undefined. If the array contains multiple elements with the specified value, there is no guarantee which one will be found. This method considers all NaN values to be equivalent and equal.

Method Syntax

public static int binarySearch(datatype[] a, dataype key)

Method Returns

The binarySearch() method returns the index of the search key, if it is contained in the array; 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 greater than the key, or a.length if all elements in the array are less than the specified key. Note that this guarantees that the return value will be >= 0 if and only if the key is found.


Requires Java 1.2 and up

Java Arrays binarySearch() Example

Below is a java code demonstrates the use of binarySearch() method of Arrays class. The example presented might be simple however it shows the behavior of the binarySearch() method.


import java.util.Arrays;

 * A java example source code to demonstrate
 * the use of binarySearch() method of Arrays class

public class ArraysBinarySearchExample {

	public static void main(String[] args) {

		// initialize a new String array
		String[] studentDatabase = new String[] { "Ryan", "Alfred", "Beth", "Vincent" };

		// sort our array

		// print the sorted array

		// search the array
		int index = Arrays.binarySearch(studentDatabase, "Beth");
		System.out.println("index is "+index);


The above java example source code demonstrates the use of binarySearch() method of Arrays class.We simply declare a new String Array that correspond to student names. As a requirement in using the binarySearch the array must be sorted so we use another static method of Arrays class which is the Arrays.sort(). After which we tested the use of binarySearch() by getting the index of one of our student name that we have initially declared.

Sample Output

Below is the sample output when you run the above example.

Arrays binarySearch() example output