Collections.min() method confusion in list of string which holds double values

Question

I have a list of strings which holds the double value. Since it holds the double value. i used Collection.min to find the minimum value in the list.

Unfortunately i get a wrong result.

What is the best way to find the smallest double value in the list of strings?

Below is the code snippet with different results.

    String a = "5.0";
    String b = "7.0";
    String c = "11.0";
    List<String> test = new ArrayList<String>();
    test.add(a);
    test.add(b);
    test.add(c);
    System.out.println(Collections.min(test)); // Result 11.0

    test = new ArrayList<String>();
    test.add(a);
    test.add(b);
    System.out.println(Collections.min(test)); // 5.0

Thanks in advance.

Answer 1

When you run Collections.min on a list of String s, you get the String that comes first in lexicographical order. That's "11.0" in your example.

You'll have to convert your List to a List<Double> in order for Collections.min to give the result you want. Alternately, use can use public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) and pass to it a Comparator<String> that parses the String s into double s and compares the doubles.

Answer 2

Quote from java Doc of Collections.min :

Returns the minimum element of the given collection, according to the natural ordering of its elements.

So the result is normal, it the natural ordering of strings.