Java 将用户指定的时间单位转换为另一个时间单位（秒到周、周到小时等）

这里是Java新手。我编写了一个时间转换程序，它接受从0到9e+18的任何数字作为有效输入，ans要求用户提供转换参数，例如从周到秒。在do-while循环中的一大块if-else-if-else行中写入所有计算。每当用户输入“q”退出时，程序就会退出。我当前的程序在不同的时间单位之间完美地进行转换

我的问题是，我如何使用switch语句来代替这个可怕的if-else语句块

if (fromUnit.equals("w") && toUnit.equals("s")) {
        results = userNumber * SECONDS_PER_WEEK;
    System.out.printf("There are %,.2f seconds", results); 
    System.out.printf(" in %,d %s.\n", userNumber, userNumber == 1 ?          "week" : "weeks");
        } else if (fromUnit.equals("h") && toUnit.equals("s")) {
    results = userNumber * SECONDS_PER_HOUR;
            System.out.printf("There are %,.2f seconds", results);
            System.out.printf(" in %,d %s.\n", userNumber, userNumber == 1 ? "hour" : "hours");
    } else if (fromUnit.equals("d") && toUnit.equals("s")) {
            results = userNumber * SECONDS_PER_DAY;
            System.out.printf("There are %,.2f seconds", results);
            System.out.printf(" in %,d %s.\n", userNumber, userNumber == 1 ? "day" : "days");
    } else if (fromUnit.equals("m") && toUnit.equals("s")) {
            results = userNumber * SECONDS_PER_MINUTE;
            System.out.printf("There are %,.2f seconds", results);
            System.out.printf(" in %,d %s.\n", userNumber, userNumber == 1 ? "minute" : "minutes");
    } else if (fromUnit.equals("s") && toUnit.equals("s")) {
            results = userNumber * SECONDS_PER_SECOND;
            System.out.printf("There are %,.2f seconds per second.\n", results);
    } else if (fromUnit.equals("w") && toUnit.equals("m")) {
            results = userNumber * MINUTES_PER_WEEK;
            System.out.printf("\nThere are %,.2f minutes", results);
            System.out.printf(" in %,d %s.\n", userNumber, userNumber == 1 ? "week" : "weeks");
    } else if (fromUnit.equals("d") && toUnit.equals("m")) {
            results = userNumber * MINUTES_PER_DAY;
            System.out.printf("\nThere are %,.2f minutes", results);
            System.out.printf(" in %,d %s.\n", userNumber, userNumber == 1 ? "day" : "days");
    } else if (fromUnit.equals("h") && toUnit.equals("m")) {
            results = userNumber * MINUTES_PER_HOUR;
            System.out.printf("\nThere are %,.2f minutes", results);
            System.out.printf(" in %,d %s.\n", userNumber, userNumber == 1 ? "hour" : "hours");
    } else if (fromUnit.equals("m") && toUnit.equals("m")) {
            results = userNumber * MINUTES_PER_MINUTE;
    System.out.printf("\nThere are %,.2f minutes", results);
            System.out.printf(" in %,d %s.\n", userNumber, userNumber == 1 ? "minute" : "minutes");
        } else if (fromUnit.equals("h") && toUnit.equals("h")) {
            results = userNumber * HOURS_PER_HOUR;
    System.out.printf("\nThere are %,.2f hours in %,d hours.\n", results, userNumber);
    } else if (fromUnit.equals("d") && toUnit.equals("h")) {
            results = userNumber * HOURS_PER_DAY;
    System.out.printf("\nThere are %,.2f hours in %,d days.\n", results, userNumber);
    } else if (fromUnit.equals("w") && toUnit.equals("h")) {
            results = userNumber * HOURS_PER_WEEK;
    System.out.printf("\nThere are %,.2f hours in %,d weeks.\n", results, userNumber);
    } else if (fromUnit.equals("d") && toUnit.equals("d")) {
            results= userNumber * DAYS_PER_DAY;
    System.out.printf("\nThere are %,.2f days in %,d days.\n", results, userNumber);
    } else if (fromUnit.equals("w") && toUnit.equals("d")) {
            results = userNumber * DAYS_PER_WEEK;
    System.out.printf("\nThere are %,.2f days in %,d weeks.\n", results, userNumber);
    } else if (fromUnit.equals("s") && toUnit.equals("ms")) {
            results = userNumber * MICROSECONDS_PER_SECOND;
            System.out.printf("\nThere are %,.3f microseconds in %,d seconds.\n", results, userNumber);
    } else if (fromUnit.equals("d") && toUnit.equals("w")) {
            results = userNumber * WEEKS_PER_DAY;
            System.out.printf("\nThere are %,.3f weeks in %,d days.\n", results, userNumber);
        } else if (fromUnit.equals("h") && toUnit.equals("d")) {
            results = userNumber * DAYS_PER_HOUR;
            System.out.printf("\nThere are %,.3f days in %,d hours.\n", results, userNumber);
    } else if (fromUnit.equals("s") && toUnit.equals("h")) {
            results = userNumber * HOURS_PER_MINUTE * MINUTES_PER_SECOND;
            System.out.printf("\nThere are %,.3f hours in %,d seconds.\n", results, userNumber);                
    } else if (fromUnit.equals("ms") && toUnit.equals("s")) {
            results = userNumber * SECONDS_PER_MICROSECOND;
            System.out.printf("\nThere are %,.3f seconds in %,d microseconds.\n", results, userNumber);
    } else if (fromUnit.equals("m") && toUnit.equals("ms")) {
    results = userNumber * MICROSECONDS_PER_MINUTE;
    System.out.printf("\nThere are %,.3f microseconds in %,d minutes.\n", results, userNumber);
        } else if (fromUnit.equals("h") && toUnit.equals("ms")) {
            results = userNumber * MICROSECONDS_PER_HOUR;
            System.out.printf("\nThere are %,.3f microseconds in %,d hours.\n", results, userNumber); 
        } else if (fromUnit.equals("d") && toUnit.equals("ms")) {
            results = userNumber * MICROSECONDS_PER_DAY;
            System.out.printf("\nThere are %,.3f microseconds in %,d days.\n", results, userNumber);
        } else if (fromUnit.equals("w") && toUnit.equals("ms")) {
            results = userNumber * MICROSECONDS_PER_WEEK;
            System.out.printf("\nThere are %,.3f microseconds in %,d weeks.\n", results, userNumber);
        } else {
            System.out.println("\nCannot calculate!\n");
    }

} while (userNumber >= 0);
}

---

}使用switch语句的一种方法是：

String fromTo = fromUnit + toUnit;

switch (fromTo) {
    case "ws": // weeks to seconds
         // ...
         break;
    case "hs": // hours to seconds
         // ...
         break;
    case "ds": // days to seconds
         // ...
         break;
    // ...
}

另一种方法是将数据放入

HashMap

HashMap map=newhashmap（）；
地图放置（“ws”，每周一秒）；
地图放置（“hs”，每小时秒）；
地图放置（“ds”，每天秒）；
// ...
字符串fromTo=fromUnit+toUnit；
结果=userNumber*map.get（fromTo）；
System.out.printf（“有%，.2f到单位”，结果）；
System.out.printf（“in%，d%s.\n”，userNumber，userNumber==1？”来自单位：“来自单位”）；

您是否查看了

开关的结构？你不懂什么？我懂开关的语法。如何编写转换结构，将周转换为秒、周转换为小时、小时转换为分钟等？我认为来自每个时间单位的每个转换都需要它自己的switch语句，对吗？这要求用户在提示输入转换参数时输入“ws”。目前，用户有3个独立的问题：首先是要转换的单位类型，然后是要转换的单位，最后是值/数字。@mchlvnctry否这不需要这些。看到第一段代码的第一行了吗？这一行将
fromUnit
和
toUnit
（来自用户的两个独立问题）连接成一个字符串。我很想使用HashMap，但因为这是Java的初学者类，我们只讨论了switch语句，所以我现在想在讲座的范围内。
HashMap<String, Integer> map = new HashMap<>();
map.put("ws", SECONDS_PER_WEEK);
map.put("hs", SECONDS_PER_HOUR);
map.put("ds", SECONDS_PER_DAY);
// ...

String fromTo = fromUnit + toUnit;
results = userNumber * map.get(fromTo);
System.out.printf("There are %,.2f to units", results);
System.out.printf(" in %,d %s.\n", userNumber, userNumber == 1 ?          "from unit" : "from units");