Find disjoint set irrespective of case of the strings

Question

I am using Collection.disjoint to find the disjoint set of two string collections c1, c2. But it does not ignore cases, for example - string str is different than Str.

return Collections.disjoint(c1, c2);

Can I find the disjoint of both collections ignoring their cases without using a for loop?

Answer 1

If you absolutely insist that no for loop is used, you can always find the disjoint between two Collections of lowercased Strings. Using Google Guava, it should be something like:

package ru.zombator.stackoverflow;

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Locale;

import com.google.common.base.Function;
import com.google.common.collect.Collections2;

public final class DisjointIgnoreCase {
    public static void main(String[] args) {
        Collection<String> coll1 = Arrays.asList("donald", "Duck");
        Collection<String> coll2 = Arrays.asList("DONALd", "Donut");
        Collection<String> coll3 = Arrays.asList("Homer", "DONUT");
        Collection<String> coll4 = Arrays.asList("DONALD", "duck");

        // will all print false
        System.out.println(disjointIgnoreCase(coll1, coll2));
        System.out.println(disjointIgnoreCase(coll2, coll3));
        System.out.println(disjointIgnoreCase(coll1, coll4));

        // will print true (no common elements)
        System.out.println(disjointIgnoreCase(coll1, coll3));
    }       

    private static boolean disjointIgnoreCase(Collection<String> coll1, Collection<String> coll2) {
        return Collections.disjoint(lowercased(coll1), lowercased(coll2));
    }       

    private static Collection<String> lowercased(Collection<String> coll) {
        return Collections2.transform(coll, new Function<String, String>() {
            @Override
            public String apply(String input) {
                return input.toLowerCase(Locale.US);
            }
        });
    }
}