从具有多个默认值的缓存中提取代码时会闻到什么味道？

Question

我们有一个包含4列的表格：

A B C VALUE  

1 2 0 100  

0 3 3 200  

0 0 7 400  

0 0 0 700  

该键由3列组成：A，B和C。

我们将此表保存在一个HashMap<ImmutableTriple<Integer, Integer, Integer>, Integer>对象上。

零代表默认值，因此在找不到确切密钥的情况下，我们应根据以下逻辑拉出相关密钥：

value = cache.get(new ImmutableTriple<>(a, b, c));

if (value != null) {

    return value;

}

value = cache.get(new ImmutableTriple<>(a, b, 0));

if (value != null) {

    return value;

}

value = cache.get(new ImmutableTriple<>(a, 0, c));

if (value != null) {

    return value;

}

value = cache.get(new ImmutableTriple<>(a, 0, 0));

if (value != null) {

    return value;

}

value = cache.get(new ImmutableTriple<>(0, 0, 0));

if (value != null) {

    return value;

}

通过具有默认值的3个ID的键获取会产生代码异味的问题。有没有更好，更清洁的方法呢？

Answer 1

有时，如果爆炸式循环使代码更具可读性，则不一定是一件坏事。我建议您将代码保持原样，因为稍后您会看到，如果您尝试对其进行压缩，则很可能会遇到更糟糕的情况。如果您坚持要继续阅读。我的想法很简单：您实际上是在尝试遍历多个掩码以用于您的匹配模式。在这种情况下，掩码为“是否使用id或默认值”。不掩饰任何东西，如果没有匹配，遮罩c，如果没有匹配项，遮罩b，如果不匹配，屏蔽bc，如果没有匹配项，屏蔽abc，如果没有匹配项，返回空值。因此，我们可以使用某种数据结构来存储掩码，如下所示：&nbsp; &nbsp; // true = use id (don't mask); false = use default (mask).&nbsp; &nbsp; List<ImmutableTriple<Boolean, Boolean, Boolean>> matchMasks = new ArrayList<>();&nbsp; &nbsp; matchMasks.add(new ImmutableTriple<>(true, true, true));&nbsp; &nbsp; matchMasks.add(new ImmutableTriple<>(true, true, false));&nbsp; &nbsp; matchMasks.add(new ImmutableTriple<>(true, false, true));&nbsp; &nbsp; matchMasks.add(new ImmutableTriple<>(true, false, false));&nbsp; &nbsp; matchMasks.add(new ImmutableTriple<>(false, false, false));当然，你可以使用List的List，Array的Array，或任何明智的存储这个面具。现在，我们可以使用循环来压缩您的代码：private Integer match(int a, int b, int c){&nbsp; &nbsp; Integer value = null;&nbsp; &nbsp; // Loop through match rules.&nbsp; &nbsp; for (ImmutableTriple<Boolean, Boolean, Boolean> mask : matchMasks)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; // Check whether to apply mask.&nbsp; &nbsp; &nbsp; &nbsp; int aId = mask.getLeft() ? a : 0;&nbsp; &nbsp; &nbsp; &nbsp; int bId = mask.getMiddle() ? b : 0;&nbsp; &nbsp; &nbsp; &nbsp; int cId = mask.getRight() ? c : 0;&nbsp; &nbsp; &nbsp; &nbsp; // Try to match cache.&nbsp; &nbsp; &nbsp; &nbsp; value = cache.get(new ImmutableTriple<>(aId, bId, cId));&nbsp; &nbsp; &nbsp; &nbsp; // Stop if match found.&nbsp; &nbsp; &nbsp; &nbsp; if (value != null) break;&nbsp; &nbsp; }&nbsp; &nbsp; return value;}全部归为一类：public class Test{&nbsp; &nbsp; private HashMap<ImmutableTriple<Integer, Integer, Integer>, Integer> cache = <your table here>;&nbsp; &nbsp; private List<ImmutableTriple<Boolean, Boolean, Boolean>> matchMasks = new ArrayList<>();&nbsp; &nbsp; public Test()&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; // true = use id (don't mask); false = use default (mask).&nbsp; &nbsp; &nbsp; &nbsp; this.matchMasks.add(new ImmutableTriple<>(true, true, true));&nbsp; &nbsp; &nbsp; &nbsp; this.matchMasks.add(new ImmutableTriple<>(true, true, false));&nbsp; &nbsp; &nbsp; &nbsp; this.matchMasks.add(new ImmutableTriple<>(true, false, true));&nbsp; &nbsp; &nbsp; &nbsp; this.matchMasks.add(new ImmutableTriple<>(true, false, false));&nbsp; &nbsp; &nbsp; &nbsp; this.matchMasks.add(new ImmutableTriple<>(false, false, false));&nbsp; &nbsp; }&nbsp; &nbsp; private Integer match(int a, int b, int c)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; Integer value = null;&nbsp; &nbsp; &nbsp; &nbsp; // Loop through match rules.&nbsp; &nbsp; &nbsp; &nbsp; for (ImmutableTriple<Boolean, Boolean, Boolean> mask : this.matchMasks)&nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Check whether to apply mask.&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; int aId = mask.getLeft() ? a : 0;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; int bId = mask.getMiddle() ? b : 0;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; int cId = mask.getRight() ? c : 0;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Try to match cache.&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = this.cache.get(new ImmutableTriple<>(aId, bId, cId));&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Stop if match found.&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; if (value != null) break;&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; return value;&nbsp; &nbsp; }}PS对于此特定情况，由于0 =默认值，因此可以为掩码使用1和0而不是true和false int aId = mask.getLeft() * a;，但这很简单。如您所见，尽管我们确实将代码“压缩”成一个循环，但其效果还是值得商de的。实际上，我认为该代码实际上不那么可读。因此，有时候，坚持使用爆炸循环并不一定很糟糕。

Answer 2

您可以使用默认值为三胞胎的所有可能状态创建“掩码映射”：private static List<Integer[]> mask = new ArrayList<>();static {&nbsp; &nbsp; mask.add(new Integer[] {null, null, null});&nbsp; &nbsp; mask.add(new Integer[] {0, null, null});&nbsp; &nbsp; mask.add(new Integer[] {null, 0, null});&nbsp; &nbsp; mask.add(new Integer[] {null, null, 0});&nbsp; &nbsp; mask.add(new Integer[] {null, 0, 0});&nbsp; &nbsp; mask.add(new Integer[] {0, null, 0});&nbsp; &nbsp; mask.add(new Integer[] {0, 0, null});&nbsp; &nbsp; mask.add(new Integer[] {0, 0, 0});}假设为null，表示必须填充键值。然后，您可以从此掩码创建三元组键的列表：List<Triple<Integer, Integer, Integer>> triples = mask.stream()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .map(row -> genrateTriple(row, a, b, c))&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .collect(Collectors.toList());generateTriplets的代码：&nbsp;private Triple<Integer, Integer, Integer> genrateTriple(Integer[] row, int... values) {&nbsp; &nbsp; int[] tripleElems = new int[3];&nbsp; &nbsp; for (int i = 0; i < row.length; i++) {&nbsp; &nbsp; &nbsp; &nbsp; tripleElems[i] = row[i] == null ? values[i] : row[i];&nbsp; &nbsp; }&nbsp; &nbsp; return new ImmutableTriple<>(tripleElems[0], tripleElems[1], tripleElems[2]);}并在搜索中使用它：return triples.stream()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;.map(triple -> cache.get(triple))&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;.findFirst()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;.orElse(null);但是我不确定这是否比您的“代码气味”;）好。编辑：当然，如果您避免创建中间集合，这会更有效（findFirst是短循环运算符）：Integer result = mask.stream()&nbsp; &nbsp; &nbsp; &nbsp; .map(row -> genrateTriple(row, a, b, c))&nbsp; &nbsp; &nbsp; &nbsp; .map(cache::get)&nbsp; &nbsp; &nbsp; &nbsp; .findFirst()&nbsp; &nbsp; &nbsp; &nbsp; .orElse(null);