Removing Duplicate elements from array is not difficult, just we have to concentrate on array index. We can remove duplicate elements from array in 2 way: using temporary array or using seperate index. For removing duplicate elements array must be sorted. You can use array.sort() in-built function or seperate programs like Selection Sort or Bubble Sort .

Java Program - Remove Duplicate Elements using Temporary Array

public class RemoveDuplicate1{
    
    public static int RemoveDuplicate(int arr[],int n){
        
        int j=0;
        
        int temp[] = new int [n];
        
        if(n==0 || n==1){
            return n;
        }
        
        for(int i=0; i<n-1;i++){
            if(arr[i]!=arr[i+1]){
                temp[j++] = arr[i];
            }
        }
        
        temp[j++] = arr[n-1]; 
        
        for(int i=0; i<j;i++){
            arr[i] = temp[i];
        }
        
        return j;
        
    }

    public static void main(String []args){
        
        int arr[] = {10, 20, 20, 30, 30, 60, 60, 70, 70};
        
        int length = arr.length;
        
        System.out.println("Without Removing Duplicate");
        
        for(int i: arr){
            System.out.print(i+"  ");
        }
        
        length = RemoveDuplicate(arr, length);
        
        System.out.println("\nAfter Removing Duplicate");
        
        for(int i=0; i<length;i++){
            System.out.print(arr[i]+"  ");
        }
        
     }
}


Java Program - Remove Duplicate Elements Using Separate Index

public class RemoveDuplicate2{
    
    public static int RemoveDuplicateIndex(int arr[],int n){
        
        int j=0;
        
        if(n==0 || n==1){
            return n;
        }
        
        for(int i=0;i<n-1;i++){
            if(arr[i]!=arr[i+1]){
                arr[j++]=arr[i];
            }
        }
        
        arr[j++]=arr[n-1];
        
        return j;
        
    }

    public static void main(String []args){
        
        int arr[] = {10, 20, 20, 30, 30, 60, 60, 70, 70, 90};
        
        int length = arr.length;
        
        System.out.println("Without Removing Duplicate");
        
        for(int i: arr){
            System.out.print(i+"  ");
        }
        
        length = RemoveDuplicateIndex(arr, length);
        
        System.out.println("\nAfter Removing Duplicate");
        
        for(int i=0; i<length;i++){
            System.out.print(arr[i]+"  ");
        }
        
     }
}