比较地图和列表时如何将 Java 7 重构为 Java 8 [关闭]答案

【问题标题】：How to refactor Java 7 as Java 8 when comparing a map and list [closed]比较地图和列表时如何将 Java 7 重构为 Java 8 [关闭]
【发布时间】：2018-04-19 22:19:35
【问题描述】：

我想重构以下代码使其更具可读性。有没有办法使用流和 lambdas 让代码更具可读性，或者让代码保持原样有意义吗？

List<Data> data = ...;
Map<String, Task> tasks = ...;
for (Data datum : data) {
    String compKey = datum.getCompKey();
    for (Map.Entry<String, Task> taskEntry : tasks.entrySet()) {
        String taskKey = taskEntry.getKey();
        Task task = taskEntry.getValue();
        if (taskKey != null && task != null) {
            String subKey = Joiner.on(".").useForNull("null").join(Arrays.copyOfRange(taskKey.split("\\."), 0, 3));
            if (compKey.equals(subKey)) {
                task.setVal1(datum.getVal1());
                task.setVal2(datum.getVal2());
                task.setVal3(datum.getVal3());                       
                break;
            }
        }
    }
}

【问题讨论】：

标签： java dictionary java-8 refactoring java-stream

【解决方案1】：

这个怎么样？

tasks.forEach((key, task) -> {
    if (key != null && task != null) {
        key = String.join(".", Arrays.asList(key.split("\\.")).subList(0, 3));
        data.stream()
            .filter(d -> d.getCompKey().equals(key))
            .findAny()
            .ifPresent(d -> {
                task.setVal1(d.getVal1());
                task.setVal2(d.getVal2());
                task.setVal3(d.getVal3());
            });
    }
});

【讨论】：

【解决方案2】：

我不会说这比您的代码更具可读性，但它表明好的 ol' for 循环仍然足够：

List<Data> data = ...;
Map<String, Task> tasks = ...;

UnaryOperator<String> function = s -> {
    return Joiner.on(".")
                 .useForNull("null")
                 .join(Arrays.copyOfRange(s.split("\\."), 0, 3));
};

data.forEach(datum -> {
    final String compKey = datum.getCompKey();

    tasks.entrySet()
         .stream()
         .filter(e -> e.getKey() != null && e.getValue() != null)
         .filter(e -> compKey.equals(function.apply(e.getKey())))
         .findFirst()
         .map(Map.Entry::getValue)
         .ifPresent(task -> {
             task.setVal1(datum.getVal1());
             task.setVal2(datum.getVal2());
             task.setVal3(datum.getVal3());
         });
});

【讨论】：