LinkedList : Collections.max() throwing NoSuchElementException

Question

I am not iterating the LinkedList by any means like scanner or other methods, I am using Collections.max() to get maximum number from the LinkedList.

I have read on Stack Overflow that this exception is thrown due to iterator or scanner or tokenizer, but I am using none of them.

import java.io.*;
import java.util.*;

class TLG {
    public static void main(String[] args)throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        LinkedList<Integer> first = new LinkedList<Integer>();
        LinkedList<Integer> second = new LinkedList<Integer>();

        int cases = Integer.parseInt(br.readLine());

        for(int i=1;i<=cases;i++) {
            String score = br.readLine();
            int number1 = Integer.parseInt(score.split(" ")[0]); 
            int number2 = Integer.parseInt(score.split(" ")[1]); 
            int diff = number1 - number2;

            if(diff > 0){
                first.add(diff);    
            }
            else {
                second.add(java.lang.Math.abs(diff));    
            }
        }

        Integer max1 = Collections.max(first);  // Getting Exception here
        Integer max2 = Collections.max(second); // Getting Exception here

        if(max1 > max2) {
            System.out.println(1+" "+max1);
        }
        else {
            System.out.println(2+" "+max2);
        }
    }
}

Can you provide some examples of input data that result in this Exception, which you believe should not? — Dancrumb, Oct 22 '14 at 18:52
Also you can't have the exception on both lines, either you get it on the first or the second. — user2336315, Oct 22 '14 at 18:53

Eran · Accepted Answer · 2023-06-08T07:43:57.937

9

You must be calling Collections.max() on an empty List.

As the Javadoc states, this results in NoSuchElementException:

<T extends Object & Comparable<? super T>> T java.util.Collections.max(Collection<? extends T> coll)

...

Throws:

ClassCastException - if the collection contains elements that are not mutually comparable (for example, strings and integers).

NoSuchElementException - if the collection is empty.

edited Jun 08 '23 at 07:43

answered Oct 22 '14 at 18:45

Eran

387,369
54
702
768

But My LInklists are not empty, I removed the Collections.max() line and printed the linked list found: 5 5 6 : None of them are empty.. 10 20 20 10 6 5 22 65 First Linkedlist element: [10, 1] Second Linkedlist element: [1, 10, 43] – PankajKushwaha Oct 22 '14 at 18:51
1

@CyberneticTwerkGuruOrc he's making a point at the cost of the quality of his answer. – Sam I am says Reinstate Monica Oct 22 '14 at 18:51
MyLinkedLists are not empty I printed them and there are values in them. – PankajKushwaha Oct 22 '14 at 18:52
3

@PankajKushwaha Then this exception cannot happen. Please try to debug your program to see what happens. – user2336315 Oct 22 '14 at 18:53

score 7 · Answer 2 · answered Oct 22 '14 at 18:57

7

you are calling Collections.max() with empty list.

answered Oct 22 '14 at 18:57

Suresh Sajja

552
3
8

score 1 · Answer 3 · answered Oct 22 '14 at 18:56

You are not checking against Empty case: So Collections.max() will throw NoSuchElementException

First check if any of the Lists is Empty (then you know the max and which list is providing it)

    Integer max;
    int list;
    if (first.isEmpty()) {
        max = Collections.max(second);
        list = 2;
    } else if (second.isEmpty()) {
        max = Collections.max(first);
        list = 1;
    } else {
        Integer max1 = Collections.max(first);
        Integer max2 = Collections.max(second);
        if (max1 > max2) {
            max = max1;
            list = 1;
        } else {
            max = max2;
            list = 2;
        }
    }
    System.out.println(list + " " + max);

You are only hiding the problem there.. The real question is why these lists are empty? — user2336315, Oct 22 '14 at 18:57
@user2336315 Not really, what if `int diff = number1 - number2;` is always positive? Then `diff` will always be on the first list — gtgaxiola, Oct 22 '14 at 19:19

LinkedList : Collections.max() throwing NoSuchElementException

3 Answers3

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