Here is the optimized solution in Java. Copy or view it below.
Java
package Problems_on_Arrays;
import java.util.*;
public class FrequencyArray {
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
System.out.println("enter the number of elements:");
int n=sc.nextInt();
int[] arr=new int[n];
HashMap<Integer,Integer> map=new HashMap<>();
for (int i=0;i<n;i++){
arr[i]=sc.nextInt();
map.put(arr[i],map.getOrDefault(arr[i],0)+1);
}
for (int i:map.keySet()){
System.out.println("the frequency of "+i+" in array is "+map.get(i));
}
sc.close();
}
}