Java Collections binarySearch() Method

The binarySearch() is an inbuilt method of Java Collections class which returns the position of the object in a sorted list. There are two different types of Java collections binarySearch() method which can be differentiated depending on its parameter.

These are:

Java Collections binarySearch(List<? extends Comparable<? super T>> list, T key)
Java Collections binarySearch(List<? extends T> list, T key, Comparator<? super T> c)

Java Collections binarySearch(List<? extends Comparable<? super T>> list, T key)

This method is used to search the provided list for the specified object using the binary search algorithm. The list must be sorted into ascending order according to the specified natural number, prior to making the method call. If the list is not sorted, the results are undefined.

Java Collections binarySearch(List<? extends T> list, T key, Comparator<? super T> c)

Syntax

Following is the declaration of binarySearch() method:

public static <T> int binarySearch(List<? extends Comparable<? super T>> list, T key)

public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c)

Parameter

Parameter	Description	Required/Optional
list	It is specified by user to be searched.	Required
key	It is the key to be searched for in the provided list.	Required
c	It is a comparator used for sorting the list.	Required

Returns

Method	Returns
binarySearch(List<? extends Comparable<? super T>> list, T key)	It returns the index of the key in a sorted list of an ascending order.
binarySearch(List<? extends T> list, T key, Comparator<? super T> c)	It returns the index of the key in a sorted list of an order defined by comparator c.

Exceptions

ClassCastException- It throws exception if the elements of the list are not mutually comparable or the search key is not mutually comparable with the elements of the list.

Compatibility Version

Java 1.5 and above

Example 1

import java.util.*;
public class CollectionsBinarySearchExample1 {
	public static void main(String[] args) {
		//Create list       
	      ArrayList<String> arrlist = new ArrayList<String>();
	      arrlist.add("A");
	      arrlist.add("B");
	      arrlist.add("C");
	      arrlist.add("D");
	      //Search the list for key 'D'
	      int index = Collections.binarySearch(arrlist, "D");     
	      System.out.println("index 'D' is available at position: "+index);
		}
}

Test it Now

Output:

index 'D' is available at position: 3

Example 2

import java.util.*;
public class CollectionsBinarySearchExample2 {
	public static void main(String[] args) {
		//Create list       
	      ArrayList<Integer> arrlist = new ArrayList<Integer>();
	      arrlist.add(10);
	      arrlist.add(-20);
	      arrlist.add(30);
	      arrlist.add(-40);
	      arrlist.add(50);
	      //Print List
	      System.out.println("Provided List are: "+arrlist);
	      //Search the list for key '-20'
	      int index = Collections.binarySearch(arrlist, -20,  Collections.reverseOrder());     
	      System.out.println("Index '-20' is available at position: "+index);
		}
}

Test it Now

Output:

Provided List are: [10, -20, 30, -40, 50]
Index '-20' is available at position: -4

Example 3

import java.util.*;
public class CollectionsBinarySearchExample3 {
	public static void main(String[] args) {		
		//Create list       
	      ArrayList<Integer> arrlist = new ArrayList<Integer>();
	      arrlist.add(10);
	      arrlist.add(-20);
	      arrlist.add(30);
	      //Print List
	      System.out.println("Provided List are: "+arrlist);
	      System.out.print("Enter the search key: ");
	      Scanner sc = new Scanner (System.in);
	      String key = sc.next();
	      int index = Collections.binarySearch(arrlist, key,  Collections.reverseOrder());     
	      System.out.println("Search Key is available at position: "+index);
	      sc.close();
		}
}

Test it Now

Output:

Provided List are: [10, -20, 30]
Enter the search key: D
Exception in thread "main" java.lang.ClassCastException: java.base/java.lang.Integer cannot be cast to java.base/java.lang.String
	at java.base/java.lang.String.compareTo(String.java:124)
	at java.base/java.util.Collections$ReverseComparator.compare(Collections.java:5140)
	at java.base/java.util.Collections$ReverseComparator.compare(Collections.java:5131)
	at java.base/java.util.Collections.indexedBinarySearch(Collections.java:333)
	at java.base/java.util.Collections.binarySearch(Collections.java:321)
	at myPackage.CollectionBinarySearchExample3.main(CollectionBinarySearchExample3.java:16)

Example 4

import java.util.*;
public class CollectionsBinarySearchExample4 {
	public static void main(String[] args) {		
		//Create list       
	      ArrayList<Integer> arlist = new ArrayList<Integer>();
	      arlist.add(5);
	      arlist.add(4);
	      arlist.add(2);
	      arlist.add(1);
	      arlist.add(3);	      
	      Collections.sort(arlist);
	      //Search for key  
	      int index = Collections.binarySearch(arlist, 4, null );     
	      System.out.println("4 is available at index: "+index);
		}
}

Test it Now

Output:

4 is available at index: 3

Example 5

import java.util.*;
public class CollectionsBinarySearchExample5 {
	public static void main(String[] args) {
	  //Create a list
        List<Domain> list = new ArrayList<Domain>();
        list.add(new Domain(10, "www.JavaTpoint.com"));
        list.add(new Domain(20, "www.sssit.com"));
        list.add(new Domain(30, "www.hindi100.com"));
        Comparator<Domain> c = new Comparator<Domain>()
        {
            public int compare(Domain u1, Domain u2)
            {
                return u1.getId().compareTo(u2.getId());
            }
        };
        /* Searching a domain with key value 10. To search
        we create an object of domain with key 10. */
        int index = Collections.binarySearch(list, new Domain(10, null), c);
        System.out.println("Available at index: " + index);
        //Searching an item with key 5
        index = Collections.binarySearch(list, new Domain(5, null), c);
        System.out.println("Found at index: " +index);
        }
}
//user-defined class to store domains with id and url
class Domain
{
    private int id;
    private String url;
    // Constructor
    public Domain(int id, String url)
    {
        this.id = id;
        this.url = url;
    }
    public Integer getId()
    {
        return Integer.valueOf(id);
    }
}

Test it Now

Output:

Available at index: 0
Found at index: -1

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Java Collections binarySearch() Method

Java Collections binarySearch(List<? extends Comparable<? super T>> list, T key)

Java Collections binarySearch(List<? extends T> list, T key, Comparator<? super T> c)

Syntax

Parameter

Returns

Exceptions

Compatibility Version

Example 1