Java Program to Find the Duplicate Values of an Array of String Values

In the previous article, we have seen Java Program to Remove Duplicate Elements in an Array

In this article we are going to find duplicates elements in a string array in Java.

Java Program to Find the Duplicate Values of an Array of String Values

Array is a data structure which stores a fixed size sequential collection of values of single type. Where with every array elements/values memory location is associated. Each array elements have it’s own index where array index starts from 0.

In Array set of variables referenced by a single variable name and it’s array index position. It is also called as a container object which contains elements of similar type.

Declaration of an array:

dataType[] arrayName; (or)                              //Declaring an array
dataType []arrayName; (or)
dataType arr[];

Instantiation of an Array:

arrayName = new datatype[size];                    //Allocating memory to array

Combining both Statements in One:

dataType[] arrayName = new dataType[size] //Declaring and Instantiating array

Initialization of an Array:

arrayName[index-0]= arrayElement1             //Initializing the array

...

arrayName[index-s]= arrayElementS

Combining all Statements in One:

dataType arrayName[ ]={e1,e2,e3};               //declaration, instantiation and initialization

Let’s see different ways to find duplicate string value in a string array.

By Static Initialization of Array Elements
By Dynamic Initialization of Array Elements

Method-1: Java Program to Find the Duplicate Values of an Array of String Values By Static Initialization of Array Elements

Approach:

Create a string array.
Display the array.
Traverse through the array and print all duplicate elements from the array by comparing them to the next element.

Program:

import java.util.*;
public class Main
{    
    public static void main(String args[])
    {
        // Crating an array
        String arr[] = {"cat", "dog", "mouse", "elephant", "cat", "mouse", "lion", "zebra"};
        // Displaying the array
        System.out.print("Array: ");
        printArray(arr);
        System.out.print("The duplicate elements are : ");
        // Print non duplicate elements
        printDupes(arr);
    }

    // Function to print the array
    static void printArray(String arr[])
    {
        for(int i = 0; i < arr.length ; i++)
            System.out.print(arr[i]+" ");
        System.out.println();
    }
    
    public static void printDupes(String arr[])
    {  
        // Counter
        int j = 0;
        // Checks for duplicate elements
        for (int i=0; i<arr.length-1; i++)
        {
            for(j=i+1;j<arr.length;j++)
                if (arr[i].equals(arr[j])&&i!=j)
                {
                    System.out.print(arr[j]+" "); 
            }  
        }
    }  
}

Output:

Array: cat dog mouse elephant cat mouse lion zebra 
The duplicate elements are : cat mouse

Method-2: Java Program to Find the Duplicate Values of an Array of String Values By Dynamic Initialization of Array Elements

Approach:

Take input of array size.
Then take input of string array elements.
Display the array.
Traverse through the array and print all duplicate elements from the array by comparing them to the next element.

Program:

import java.util.*;
public class Main
{    
    public static void main(String args[])
    {
        Scanner sc = new Scanner(System.in); 
        System.out.print("Enter the number of elements in the array: "); 
        int num = sc.nextInt(); 
        String arr[] = new String[num]; 
        System.out.println("Enter the elements: "); 
        for (int i = 0; i <arr.length; i++) 
        { 
            arr[i] = sc.next(); 
        }
        
        // Displaying the array
        System.out.print("Array: ");
        printArray(arr);
        System.out.print("The duplicate elements are : ");
        // Print non duplicate elements
        printDupes(arr);
    }

    // Function to print the array
    static void printArray(String arr[])
    {
        for(int i = 0; i < arr.length ; i++)
            System.out.print(arr[i]+" ");
        System.out.println();
    }
    
    public static void printDupes(String arr[])
    {  
        // Counter
        int j = 0;
        // Checks for duplicate elements
        for (int i=0; i<arr.length-1; i++)
        {
            for(j=i+1;j<arr.length;j++)
                if (arr[i].equals(arr[j])&&i!=j)
                {
                    System.out.print(arr[j]+" "); 
            }  
        }
    }  
}

Output:

Enter the number of elements in the array: 5
Enter the elements: 
rat
cat
bat
rat
mat
Array: rat cat bat rat mat 
The duplicate elements are : rat

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