java - 查找不相交的集合而不考虑字符串的大小写

Question

我正在使用 Collection.disjoint找到两个字符串集合的不相交集 c1, c2. 但它不会忽略大小写，例如 - 字符串 str 与 Str 不同.

return Collections.disjoint(c1, c2);

我能否在不使用 for 循环的情况下找到两个集合的不相交而忽略它们的大小写？

Answer 1

如果您绝对坚持不使用 for 循环，您总能找到两个小写 String 的 Collection 之间的不相交。使用 Google Guava ，它应该是这样的:

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);
            }
        });
    }
}