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Check array for duplicates in Java Code Examples

Last Updated on Wednesday 5th Oct 2022

java find duplicates in array

Example 1 Using Loops

  • Check for every array element is repeated or not using nested for-loops.
			
					public class main {

  public static boolean chkForDup(String[] arr) {
    for (int i = 0; i < arr.length; i++) {
      for (int j = 0; j < arr.length; j++) {
        if (arr[i].equals(arr[j]) && i != j) {
          return true;
        }
      }
    }
    return false;
  }
  public static void main(String[] args) {
    String[] grps = {
      "one",
      "two",
      "three",
      "one"
    };
    boolean result = chkForDup(grps);
    System.out.println(result);
  }
}

The Above Code Outputs the

			
					// true

Exmaple 2: Using HashSet

			
					import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
public class main {
  public static List < Integer > findDuplicates(int[] nums) {
    List < Integer > duplicateVal = new ArrayList < > ();
    HashSet < Integer > set = new HashSet < Integer > ();
    for (int val: nums) {
      if (!set.add(val)) {
        duplicateVal.add(val);
      }
    }
    return duplicateVal;

  }
  public static void main(String[] args) {
    int[] arr = new int[] {
      1,
      2,
      3,
      4,
      2,
      7,
      8,
      8,
      3,
      7
    };

    List < Integer > duplicatesVal;
    duplicatesVal = findDuplicates(arr);
    for (Integer val: duplicatesVal) {
      System.out.print(val + "  ");
    }
  }
}

The Above Code Outputs the

			
					// 2  8  3  7