How is 1 greater than 4?

Question

The NavigableSet.lower(E) Javadoc says it returns the greatest element in this set strictly less than the given element, or null if there is no such element. Why is 1 the output here? Shouldn't it be 4?

NavigableSet original = new TreeSet();
original.add("1");
original.add("2");
original.add("3");
original.add("4");
original.add("10");
Object lower = original.lower("10");
System.out.println(lower);

Answer 1

Because the values are String(s) the Set is comparing by lexical order. Please, don't use Raw Types.

NavigableSet<Integer> original = new TreeSet<>();
original.add(1);
original.add(2);
original.add(3);
original.add(4);
original.add(10);
Object lower = original.lower(10);
System.out.println(lower);

Output is

4

Answer 2

thats because you are comparing Strings here, and not as assumed integers. So the actual order in the Set is : 1, 10, 2, 3, 4 !

Use the generics : NavigableSet<Integer> original = new TreeSet<>(); and add the values as integers : original.add(1); and so on.