Move a specific element in arraylist to the last index

Let's say I have this List

List<Integer> grades = Arrays.asList(9,8,1,0,7,0,0,3);

I want to move all zeros to the last indexes .. So I want the output to be something like:

9,8,1,7,3,0,0,0

I can do that with simple arrays but I still didn't figure out how to do that in ArrayList.

You can sort the list accordingly using Comparator.comparing, to move all 0 to last and not to sort the remaining values

grades.sort(Comparator.comparing(value -> value == 0 ? 1 /* sort last */ : 0 /* don't sort */));  //[9, 8, 1, 7, 3, 0, 0, 0]

As noted in the comments, you could reuse the same code you have for arrays by using the List's get and set methods instead of the [] operator.

Another "sneaky" approach could be to utilize the fact that sorting keeps the relative positions of two elements that are equivalent, and sort the list with a custom Comparator that sorts according to whether or not an item is equal to 0 - all the zeros will moved to the end, and all the other items will keep their relative postions:

grades.sort(Comparator.comparing(i -> i == 0));

For a faster O(n) implementation than using an O(n log(n)) sort() solution, do it the same way you'd do it for an array:

int j = 0;
for (Integer value : grades) {
	if (value != 0) {
		grades.set(j++, value);
	}
}
while (j < grades.size()) {
	grades.set(j++, 0);
}

Of course, using set(int, ?) can be bad for performance if not an ArrayList, so it'd be better to use an updatable iterator, i.e. a ListIterator:

ListIterator<Integer> iter = grades.listIterator();
for (Integer value : grades) {
	if (value != 0) {
		iter.next(); // No need to call hasNext() first
		iter.set(value);
	}
}
while (iter.hasNext()) {
	iter.next();
	iter.set(0);
}

For comparison, here is the comparable array solution:

int[] grades = {9,8,1,0,7,0,0,3};

int j = 0;
for (int i = 0; i < grades.length; i++) {
	if (grades[i] != 0) {
		grades[j++] = grades[i];
	}
}
while (j < grades.length) {
	grades[j++] = 0;
}

Thanks guys ..

I managed to do it the same way I did it with simple arrays :

 List<Integer> price = Arrays.asList(9,8,1,0,7,0,0,3);
       
        
        int count = 0;
        
        
        for(int i=0; i<price.size(); i++) {
        	if(price.get(i) !=0) {
        		
        		price.set(count++, price.get(i));	
        		
        	}
        	
        }
        	 while(count<price.size()) {
             	price.set(count++, 0);
             
             	
             }
        	System.out.print(Arrays.toString(price.toArray()));
        }