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How to perform Linear and Binary Search in Java ?.

Updated on September 17, 2014

Introduction

In this tutorial, you will learn concept of searching in Java. Searching is the process of finding an specified element from the collection of elements. Usually, searching involves finding elements from database records, text files, arrays etc. Generally, search algorithms are of two types Linear Search and Binary Search.

Linear Search as the name suggest performs search in a linearly or sequential manner. Binary Search does not performs search linearly or sequential way. It performs a search in a non - linear manner. It is similar to a dictionary search, where we perform search based on divide and conquer algorithm.

In this tutorial, you will learn both concepts of searching, Linear as well as Binary Search. Below you will come across complete Java implementation of Linear and Binary Search. The code is highly commented to make you understand the concept of searching.

Video tutorial - How to perform Linear and Binary Search in Java.

Linear Search code in Java

Linear Search class in Java.
Linear Search class in Java.

Linear Search class in Java

// Step 1 - Create a Java class.
public class LinearSearch {

	// Step 2 - Create a static method, taking in an integer array and 
	// key to be search in the array.
	public static int linearSearch(int[ ] array, int key) {
		
		// Step 3 - In order to search a key in the integer array.
		// We iterate each element of array and check its 
		// equality with the key. In our case we use a for loop 
		// which will iterate over an array from its 0 index to 
		// length of array - 1. 
		for (int i = 0; i < array.length; i++) {
			
			// Step 4 - With each and every element in the for loop
			// we will check whether a key is equal to element in the array.
			// If key == array[i] comes out to be true, than it is confirmed that
			// element is found in the array.
			if (key == array[i])
			    
				// Step 5 - We return index of array on which element is found. 
				return i;
		}
		// Step 6 - If no match is found than return integer value as -1 signifying 
		// key not found in array.
		return -1;
	}
}

Steps to implement -

Step 1 - Create a Java class.

Step 2 - Create a static method, taking in an integer array and key to be search in the array.

Step 3 - In order to search a key in the integer array. We iterate each element of array and check its equality with the key. In our case we use a for loop which will iterate over an array from its 0 index to length of array - 1.

Step 4 - With each and every element in the for loop we will check whether a key is equal to element in the array.If key == array[i] comes out to be true, than it is confirmed that element is found in the array.

Step 5 - We return index of array on which element is found.

Step 6 - If no match is found than return integer value as -1 signifying key not found in array.


Binary Search code in Java

Binary Search class in Java.
Binary Search class in Java.

Binary Search class in Java

// Step 1 - Create a Java class.
public class BinarySearch {

	// Step 2 - Create a static method, taking in an integer array and 
	// key to be search in the array.
	public static int binarySearch(int[ ] array, int key) {
		
		// Step 3 - Create two integer variable high and low. Assign value 0 
		// to low and last index of array to high i.e. array.length - 1.
		int low = 0;
		int high = array.length - 1;

		// Step 4 - Apply while loop till value of low is lower than value of 
		// high.
		while(low <= high) {
			
			// Step 5 - Create a integer variable by name mid. It holds the middle
			// value between low and high. In each iteration this step is to be
			// performed. It helps in searching of key faster. As with each iteration half of 
			// the values in array are discarded, based on below if condition.
			int mid = (low + high) / 2;
			
			// Step 6 - Check whether key to be search is less than middle element of array. 
			// If the check comes out to be true, it confirms that key is in lower half of array. 
			// Upper half is therefore discarded based on this check.
			if (key < array[mid]) {
				
				// Step 7 - If the above check comes out to be true than key is somewhere in 
				// lower half of array. Therefore our new high becomes mid - 1 and same 
				// check is applied over each iteration to come closer to key.
				high = mid - 1;
			}
			// Step 8 - If key is not less than middle element. We apply a check whether 
			// middle element is the key we are searching for.
			else if (key == array[mid]) {
				
				// Step 9 - If the middle element is equal to the key to be searched, than return 
				// the index of middle element.
				return mid; 
			}
			
			// Step 10 - If the middle element is not equal to key, than it is confirmed that 
			// key we are searching for lies in the upper half of array. Therefore, our new low
			// becomes mid + 1 and same check is applied over each iteration to come closer to key.
			else {
				low = mid + 1;
			}
		}
		
		// Step 11 - If key is not found in while loop return -1 to signify that key is not found in array. 
		return -1;
	}	
}

Steps to implement -

Step 1 - Create a Java class.

Step 2 - Create a static method, taking in an integer array and key to be search in the array.

Step 3 - Create two integer variable high and low. Assign value 0 to low and last index of array to high i.e. array.length - 1.

Step 4 - Apply while loop till value of low is lower than value of high.

Step 5 - Create a integer variable by name mid. It holds the middle value between low and high. In each iteration this step is to be performed. It helps in searching of key faster. As with each iteration half of the values in array are discarded, based on below if condition.

Step 6 - Check whether key to be search is less than middle element of array. If the check comes out to be true, it confirms that key is in lower half of array. Upper half is therefore discarded based on this check.

Step 7 - If the above check comes out to be true than key is somewhere in lower half of array. Therefore our new high becomes mid - 1 and same check is applied over each iteration to come closer to key.

Step 8 - If key is not less than middle element. We apply a check whether middle element is the key we are searching for.

Step 9 - If the middle element is equal to the key to be searched, than return the index of middle element.

Step 10 - If the middle element is not equal to key, than it is confirmed that key we are searching for lies in the upper half of array. Therefore, our new low becomes mid + 1 and same check is applied over each iteration to come closer to key.

Step 11 - If key is not found in while loop return -1 to signify that key is not found in array.

Search test class in Java

Linear and Binary Search Test class.
Linear and Binary Search Test class.

Linear and Binary Search Test class

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

		// Step 1 - In the main method create an array of few elements.
		int[ ] array = { 1, 2, 3, 4, 5, 8, 9, 10, 12};
		
		// Step 2 - Create a key to search in the array.
		int key = 8; 
		
		// Step 3 - Call linearSearch method with array and key to search.
		int result = LinearSearch.linearSearch(array, key);
		
		// Step 4 - In our case 8 is there in array so result will not be equal to -1.
		// Hence, below if check comes out to be true and index of found key is
		// printed on the console.
		if(result != -1) {
			System.out.println("Key " + key + " found at index -  " + result);
		} else { 
			System.out.println("Key "+ key + " not found !!!");
		}

		// Step 5 - Perform steps with a different key with binarySearch method.
		key = 10; 
		result = BinarySearch.binarySearch(array, key);
		
		if(result != -1) {
			System.out.println("Key " + key + " found at index -  " + result);
		} else { 
			System.out.println("Key "+ key + " not found !!!");
		}		
	}
}

Steps to implement -

Step 1 - In the main method create an array of few elements.

Step 2 - Create a key to search in the array.

Step 3 - Call linearSearch method with array and key to search.

Step 4 - In our case 8 is there in array so result will not be equal to -1. Hence, below if check comes out to be true and index of found key is printed on the console.

Step 5 - Perform steps with a different key with binarySearch method.


Output of the program -

Output of Linear and Binary Search program.
Output of Linear and Binary Search program.

Output of the program - Explanation

In the SearchTest class, we have created an array with few elements such as, 1, 2, 3, 4, 5, 8, 9, 10, 12. We take two keys 8 and 10, which are present in the array. One key is used to demonstrate linear search and other used to demonstrate binary search. Both the methods output as :

Key 8 found at index - 5
Key 10 found at index - 7

Hope you like this tutorial on Searching in Java. Please, do visit my other good Java tutorials.


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