Java program to Remove Duplicate Elements From an Array

In this post of Java program to Remove Duplicate Elements From an Array We will look into three different methods to remove duplicate elements from an array.

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Java program to Remove Duplicate Elements From an Array using Collection APIs

package com.kkjavatutorials.client;

import java.util.HashSet;
import java.util.Set;

/**
 * @author KK JavaTutorials 
 * Java program to Remove Duplicate Elements From an Array using Collection APIs
 */
public class RemoveDuplicateElementsFromArray1 {

	public static void main(String[] args) {
		int[] inputArrayWithDupElements = { 5, 8, 5, 50, 26, 26, 100, 1001, 5, 120};
		Integer[] outputArrayWithoutDupElements = removeDuplicatesUsingSet(inputArrayWithDupElements);
	
		System.out.println("Original array::::");
		for (int element : inputArrayWithDupElements) {
			System.out.println(element);
		}
		
		System.out.println("After Duplicate Elements removal array:::");
		for (int element : outputArrayWithoutDupElements) {
			System.out.println(element);
		}
	}

	//Method to remove duplicate elements from an array
	public static Integer[] removeDuplicatesUsingSet(int[] input) {
		//Adding each array element to a Set
		Set<Integer> set = new HashSet<Integer>();
		for (int element : input) {
			set.add(element);
		}
				
		Integer[] outputArrayWithoutDupElements = set.toArray(new Integer[set.size()]);
		return outputArrayWithoutDupElements;
	}
}

package com.kkjavatutorials.client;

import java.util.HashSet;

import java.util.Set;

/**

* @author KK JavaTutorials

* Java program to Remove Duplicate Elements From an Array using Collection APIs

public class RemoveDuplicateElementsFromArray1 {

public static void main(String[] args) {

int[] inputArrayWithDupElements = { 5, 8, 5, 50, 26, 26, 100, 1001, 5, 120};

Integer[] outputArrayWithoutDupElements = removeDuplicatesUsingSet(inputArrayWithDupElements);

System.out.println("Original array::::");

for (int element : inputArrayWithDupElements) {

System.out.println(element);

}

System.out.println("After Duplicate Elements removal array:::");

for (int element : outputArrayWithoutDupElements) {

System.out.println(element);

}

//Method to remove duplicate elements from an array

public static Integer[] removeDuplicatesUsingSet(int[] input) {

//Adding each array element to a Set

Set<Integer> set = new HashSet<Integer>();

for (int element : input) {

set.add(element);

}

Integer[] outputArrayWithoutDupElements = set.toArray(new Integer[set.size()]);

return outputArrayWithoutDupElements;

}

Output of program::

Original array::::
5
8
5
50
26
26
100
1001
5
120
After Duplicate Elements removal array:::
50
100
5
8
120
1001
26

Original array::::

100

1001

120

After Duplicate Elements removal array:::

100

120

1001

2. Java program to Remove Duplicate Elements From an Array without using Collection APIs

package com.kkjavatutorials.client;

import java.util.Arrays;
/**
 * @author KK JavaTutorials 
 * Java program to Remove Duplicate Elements From an Array without using Collection APIs
 */
public class RemoveDuplicateElementsFromArray2 {

	public static void main(String[] args) {
		int[] inputArrayWithDupElements = { 5, 8, 5, 50, 26, 26, 100, 1001, 5, 120};
		System.out.println("Original array::::");
		for (int element : inputArrayWithDupElements) {
			System.out.println(element);
		}
		
		int[] outputArrayWithoutDupElements = removeDuplicateElementsFromArray(inputArrayWithDupElements);
		System.out.println("After Duplicate Elements removal array:::");
		for (int element : outputArrayWithoutDupElements) {
			System.out.println(element);
		}
	}

	//Method to remove duplicate elements from an array
	public static int[] removeDuplicateElementsFromArray(int[] inputArrayWithDupElements) {
		int i = 1;
		int j = 0;
		Arrays.sort(inputArrayWithDupElements);
		
		while (i < inputArrayWithDupElements.length) {
			if (inputArrayWithDupElements[i] == inputArrayWithDupElements[j]) {
				i++;
			} else {
				inputArrayWithDupElements[++j] = inputArrayWithDupElements[i++];
			}
		}
		/*If array has duplicate elements then after removing duplicate elements
		This is required to truncate the size of the array otherwise array will retain its original size
		*/
		int[] output = Arrays.copyOf(inputArrayWithDupElements, j + 1);
		return output;
	}
}

package com.kkjavatutorials.client;

import java.util.Arrays;

/**

* @author KK JavaTutorials

* Java program to Remove Duplicate Elements From an Array without using Collection APIs

public class RemoveDuplicateElementsFromArray2 {

public static void main(String[] args) {

int[] inputArrayWithDupElements = { 5, 8, 5, 50, 26, 26, 100, 1001, 5, 120};

System.out.println("Original array::::");

for (int element : inputArrayWithDupElements) {

System.out.println(element);

}

int[] outputArrayWithoutDupElements = removeDuplicateElementsFromArray(inputArrayWithDupElements);

System.out.println("After Duplicate Elements removal array:::");

for (int element : outputArrayWithoutDupElements) {

System.out.println(element);

}

//Method to remove duplicate elements from an array

public static int[] removeDuplicateElementsFromArray(int[] inputArrayWithDupElements) {

int i = 1;

int j = 0;

Arrays.sort(inputArrayWithDupElements);

while (i < inputArrayWithDupElements.length) {

if (inputArrayWithDupElements[i] == inputArrayWithDupElements[j]) {

i++;

} else {

inputArrayWithDupElements[++j] = inputArrayWithDupElements[i++];

}

/*If array has duplicate elements then after removing duplicate elements

This is required to truncate the size of the array otherwise array will retain its original size

int[] output = Arrays.copyOf(inputArrayWithDupElements, j + 1);

return output;

}

Output of program::

Original array::::
5
8
5
50
26
26
100
1001
5
120
After Duplicate Elements removal array:::
5
8
26
50
100
120
1001

Original array::::

100

1001

120

After Duplicate Elements removal array:::

100

120

1001

3. Java program to Remove Duplicate Elements From an Array using Java 8 Stream APIs

package com.kkjavatutorials.client;

import java.util.Arrays;

/**
 * @author KK JavaTutorials 
 * Java program to Remove Duplicate Elements From an Array using Java 8 Stream APIs
 */
public class RemoveDuplicateElementsFromArray3 {

	public static void main(String[] args) {
		int[] inputArrayWithDupElements = { 5, 8, 5, 50, 26, 26, 100, 1001, 5, 120 };
		System.out.println("Original array::::");
		for (int element : inputArrayWithDupElements) {
			System.out.println(element);
		}

		int outputArrayWithoutDupElements[] = Arrays.stream(inputArrayWithDupElements).distinct().toArray();
		System.out.println("After Duplicate Elements removal array:::");
		for (int element : outputArrayWithoutDupElements) {
			System.out.println(element);
		}

	}
}

package com.kkjavatutorials.client;

import java.util.Arrays;

/**

* @author KK JavaTutorials

* Java program to Remove Duplicate Elements From an Array using Java 8 Stream APIs

public class RemoveDuplicateElementsFromArray3 {

public static void main(String[] args) {

int[] inputArrayWithDupElements = { 5, 8, 5, 50, 26, 26, 100, 1001, 5, 120 };

System.out.println("Original array::::");

for (int element : inputArrayWithDupElements) {

System.out.println(element);

}

int outputArrayWithoutDupElements[] = Arrays.stream(inputArrayWithDupElements).distinct().toArray();

System.out.println("After Duplicate Elements removal array:::");

for (int element : outputArrayWithoutDupElements) {

System.out.println(element);

}

Output of program::

Original array::::
5
8
5
50
26
26
100
1001
5
120
After Duplicate Elements removal array:::
5
8
50
26
100
1001
120

Original array::::

100

1001

120

After Duplicate Elements removal array:::

100

1001

120

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