leetcode--Largest Number

Given a list of non negative integers, arrange them such that they form the largest number.

For example, given [3, 30, 34, 5, 9], the largest formed number is 9534330.

Note: The result may be very large, so you need to return a string instead of an integer.

public class Solution {
    public String largestNumber(int[] nums) {
		ArrayList<Integer> arr = new ArrayList<>();
		for(int i=0;i<nums.length;i++){
			arr.add(nums[i]);
		}
		Collections.sort(arr, new Comparator<Integer>() {
			@Override
			public int compare(Integer o1, Integer o2) {								
				String str1 = o1+""+o2;
				String str2 = o2+""+o1;
				return str2.compareTo(str1);
			}
		});
		if(arr.get(0)==0) return "0";
		StringBuilder sb = new StringBuilder();
		for(Integer i:arr){
			sb.append(i);
		}
		return sb.toString();		
    }
}