Java: Print after removing duplicates from a given string

Last update on May 21 2025 12:49:16 (UTC/GMT +8 hours)

38. Remove Duplicate Characters

Write a Java program to print the result of removing duplicates from a given string.

Visual Presentation:

Sample Solution:

Java Code:

// Importing necessary Java utilities.
import java.util.*;

// Define a class named Main.
public class Main {
    
    // Main method to execute the program.
    public static void main(String[] args) {
        // Declare and initialize a string variable.
        String str1 = "w3resource";
        
        // Print the original string.
        System.out.println("The given string is: " + str1);
        
        // Print the new string after removing duplicate characters.
        System.out.println("After removing duplicates characters the new string is: " + removeDuplicateChars(str1));
    }
    
    // Method to remove duplicate characters from a string.
    private static String removeDuplicateChars(String sourceStr) {
        // Convert the input string to a character array.
        char[] arr1 = sourceStr.toCharArray();
        
        // Initialize an empty string to store the resulting string without duplicates.
        String targetStr = "";
        
        // Loop through each character in the character array.
        for (char value: arr1) {
            // Check if the character doesn't exist in the targetStr.
            if (targetStr.indexOf(value) == -1) {
                // If the character doesn't exist, add it to the targetStr.
                targetStr += value;
            }
        }
        
        // Return the resulting string without duplicates.
        return targetStr;
    }
}

Sample Output:

The given string is: w3resource
After removing duplicates characters the new string is: w3resouc

Flowchart:

Remove duplicate characters from a given string.

Main.java Code:

//MIT License: https://bit.ly/35gZLa3
import java.util.concurrent.TimeUnit;

public class Main {

    private static final String TEXT = "!ABCBA;C D E-D  D  DFA;";

    public static void main(String[] args) {

        System.out.println("Input text: \n" + TEXT + "\n");

        System.out.println("StringBuilder and indexOf() solution:");
        long startTimeV1 = System.nanoTime();

        String resultV1 = Strings.removeDuplicatesV1(TEXT);

        displayExecutionTime(System.nanoTime() - startTimeV1);
        System.out.println("String with no duplicates: \n" + resultV1);

        System.out.println();
        System.out.println("LinkedHashSet and StringBuilder solution:");
        long startTimeV2 = System.nanoTime();

        String resultV2 = Strings.removeDuplicatesV2(TEXT);

        displayExecutionTime(System.nanoTime() - startTimeV2);
        System.out.println("String with no duplicates: \n" + resultV2);

        System.out.println();
        System.out.println("Java 8, functional-style solution:");
        long startTimeV3 = System.nanoTime();

        String resultV3 = Strings.removeDuplicatesV3(TEXT);

        displayExecutionTime(System.nanoTime() - startTimeV3);
        System.out.println("String with no duplicates: \n" + resultV3);
    }

    private static void displayExecutionTime(long time) {
        System.out.println("Execution time: " + time + " ns" + " ("
                + TimeUnit.MILLISECONDS.convert(time, TimeUnit.NANOSECONDS) + " ms)");
    }
}

Strings.java Code:

//MIT License: https://bit.ly/35gZLa3
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
import java.util.stream.Collectors;

public final class Strings {

    private Strings() {
        throw new AssertionError("Cannot be instantiated");
    }

    public static String removeDuplicatesV1(String str) {

        if (str == null || str.isEmpty()) {
            // or throw IllegalArgumentException
            return "";
        }

        char[] chArray = str.toCharArray();
        StringBuilder sb = new StringBuilder();
        for (char ch : chArray) {
            if (sb.indexOf(String.valueOf(ch)) == -1) {
                sb.append(ch);
            }
        }

        return sb.toString();
    }

    public static String removeDuplicatesV2(String str) {

        if (str == null || str.isEmpty()) {
            // or throw IllegalArgumentException
            return "";
        }

        char[] chArray = str.toCharArray();
        StringBuilder sb = new StringBuilder();
        Set<Character> chHashSet = new HashSet<>();
        for (char c : chArray) {
            if (chHashSet.add(c)) {
                sb.append(c);
            }

        }
        return sb.toString();
    }

    public static String removeDuplicatesV3(String str) {

        if (str == null || str.isEmpty()) {
            // or throw IllegalArgumentException
            return "";
        }

        return Arrays.asList(str.split("")).stream()
                .distinct()
                .collect(Collectors.joining());
    }
}

Sample Output:

Input text: 
!ABCBA;C D E-D  D  DFA;

StringBuilder and indexOf() solution:
Execution time: 760557 ns (0 ms)
String with no duplicates: 
!ABC; DE-F

LinkedHashSet and StringBuilder solution:
Execution time: 705992 ns (0 ms)
String with no duplicates: 
!ABC; DE-F

Java 8, functional-style solution:
Execution time: 84676685 ns (84 ms)
String with no duplicates: 
!ABC; DE-F

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to remove all duplicate characters from a string while preserving the original order.
• Write a Java program to eliminate duplicate characters from a string and then reverse the resulting string.
• Write a Java program to remove duplicates from a string and count the number of characters removed.
• Write a Java program to filter out duplicate characters from a string and display only the unique ones in alphabetical order.

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