1

我有以下一段代码。

import java.util.Arrays;
import java.util.Collections;
import java.util.Map;
import java.util.TreeMap;
import java.util.stream.Collectors;

public final class Main {
    public static void main(final String[] args) {
        final Object[][] pairs = { { "Arka Gdynia", Collections.emptyList() },
                { "Legia Warszawa", Collections.emptyList() }, { "ŁKS Łódź", Collections.emptyList() },
                { "Śląsk Wrocław", Collections.emptyList() }, { "Wisła Kraków", Collections.emptyList() }, };

        final Map<String, Object> clubPlayerMap = Arrays.stream(pairs)
                .collect(Collectors.toMap(c -> c[0].toString(), c -> c[1], (o1, o2) -> o1, TreeMap::new));
        for (final String key : clubPlayerMap.keySet()) {
            System.out.println(key);
        }
    }
}

不幸的是，这不会产生我想要的结果。键需要根据波兰排序规则进行排序。

Arka Gdynia
Legia Warszawa
Wisła Kraków
ŁKS Łódź
Śląsk Wrocław

我期望的结果是

Arka Gdynia
Legia Warszawa
ŁKS Łódź
Śląsk Wrocław
Wisła Kraków

所以我用谷歌搜索并找到了一种方法来做到这一点java.text.Collator。stream()但是，我想知道是否可以将其与和一起作为单行来执行collect()。

我想出的解决方案如下，但不幸的是它不是很整洁。

import java.text.Collator;
import java.util.Arrays;
import java.util.Collections;
import java.util.Locale;
import java.util.Map;
import java.util.TreeMap;
import java.util.stream.Collectors;

public final class Main {
    public static void main(final String[] args) {
        final Object[][] pairs = { { "Arka Gdynia", Collections.emptyList() },
                { "Legia Warszawa", Collections.emptyList() }, { "ŁKS Łódź", Collections.emptyList() },
                { "Śląsk Wrocław", Collections.emptyList() }, { "Wisła Kraków", Collections.emptyList() }, };

        final Map<String, Object> clubPlayerMapCollated = new TreeMap<>(Collator.getInstance(new Locale("pl", "PL")));
        final Map<String, Object> clubPlayerMap = Arrays.stream(pairs)
                .collect(Collectors.toMap(c -> c[0].toString(), c -> c[1], (o1, o2) -> o1, TreeMap::new));
        clubPlayerMapCollated.putAll(clubPlayerMap);
        for (final String key : clubPlayerMapCollated.keySet()) {
            System.out.println(key);
        }
    }
}

是否有可能从单线生成地图？

4

1 回答 1

2

不要将方法引用传递给默认构造函数 ( TreeMap::new)，而是传递一个 lambda 表达式，该表达式将生成所需的TreeMap：

final Map<String, Object> clubPlayerMap = 
    Arrays.stream(pairs)
          .collect(Collectors.toMap(c -> c[0].toString(), 
                                    c -> c[1], 
                                    (o1, o2) -> o1, 
                                    () -> new TreeMap<>(Collator.getInstance(new Locale("pl", "PL")))));
于 2019-12-22T11:56:48.947 回答