java - 这些 "if statements"可以简化吗？

Question

我有以下方法:

public static String format_String(int hours, int minutes, int seconds)
{   
    if(hours > 0 && minutes > 0 && seconds > 0) return hours + " hours, " + minutes + " minutes and " + seconds + " seconds.";
    else if(hours > 0 && minutes > 0 && seconds == 0) return hours + " hours and " + minutes + " minutes.";
    else if(hours > 0 && minutes == 0 && seconds > 0) return hours + " hours and " + seconds + " seconds.";
    else if(hours > 0 && minutes == 0 && seconds == 0) return hours + " hours.";
    else if(hours == 0 && minutes > 0 && seconds > 0) return minutes + " minutes and " + seconds + " seconds.";
    else if(hours == 0 && minutes > 0 && seconds == 0) return minutes + " minutes.";
    else //if(hours == 0 && minutes == 0 && seconds > 0)
    return seconds + " seconds.";
}

这个方法可以简化吗？

Answer 1

比较棘手的是用"和"还是","来分隔部分，这取决于该部分右边出现了多少个非零部分您目前正在打印。剩下的(打印姓名和号码)很简单。

因此，您可以通过从右到左构建字符串来减少分支数。

public static String format_String(int hours, int minutes, int seconds)
{
    StringBuilder result = new StringBuilder(".");
    String sep = "", nextSep = " and ";
    if (seconds > 0) {
        result.insert(0, " seconds").insert(0, seconds);
        sep = nextSep;
        nextSep = ", ";
    }
    if (minutes > 0) {
        result.insert(0, sep).insert(0, " minutes").insert(0, minutes);
        sep = nextSep;
        nextSep = ", ";
    }
    if (hours > 0) {
        result.insert(0, sep).insert(0, " hours").insert(0, hours);
    }
    return result.toString();
}

或更一般地说:

public static String formatString(SortedMap<TimeUnit, Integer> parts) {
    StringBuilder result = new StringBuilder(".");
    String sep = "", nextSep = " and ";
    for (Map.Entry<TimeUnit, Integer> e: parts.entrySet()) {
        TimeUnit field = e.getKey();
        Integer quantity = e.getValue();
        if (quantity > 0) {
            result.insert(0, sep)
                  .insert(0, field.toString().toLowerCase())
                  .insert(0, ' ')
                  .insert(0, quantity);
            sep = nextSep;
            nextSep = ", ";
        }
    }
    return result.toString();
}