Question

我目前正在从一本书中学习java，一个项目是在输入月份数后输出一个月的日期和月份名称。我想知道是否有更好的方法来设置我的if语句而不是我已经完成的事情。

PS：控制台阅读器只是一个包含的类，可以轻松地从用户控制台获取输入。

public class Project13 {

public static void main(String[] args) {
    ConsoleReader console = new ConsoleReader(System.in);

    System.out.println("Enter a month you would like to evaluate (by number):");
    int month = console.readInt();

    int days = 0;
    String monthout = "Month";
    String out = "Yes";
    if(month == 1){
        days = 31;
        monthout = "January";
        out = "There are " + days + " days in " + monthout;
    }else if(month == 2){
        System.out.println("Is it a leap year? Yes or No:");
        String leap = console.readLine(); 
        if(leap.equalsIgnoreCase("yes")){
            days = 29;
            monthout = "February";
            out = "There are " + days + " days in " + monthout;
        }else if(leap.equalsIgnoreCase("no")){
            days = 28;
            monthout = "February";
            out = "There are " + days + " days in " + monthout;
        }else{
            out = "Something went wrong, please try again";
        }
    }else if(month == 3){
        days = 31;
        monthout = "March";
        out = "There are " + days + " days in " + monthout;
    }else if(month == 4){
        days = 30;
        monthout= "April";
        out = "There are " + days + " days in " + monthout;
    }else if(month == 5){
        days = 31;
        monthout = "May";
        out = "There are " + days + " days in " + monthout;
    }else if(month == 6){
        days = 30;
        monthout = "June";
        out = "There are " + days + " days in " + monthout;
    }else if(month == 7){
        days = 31;
        monthout = "July";
        out = "There are " + days + " days in " + monthout;
    }else if(month == 8){
        days = 31;
        monthout = "August";
        out = "There are " + days + " days in " + monthout;
    }else if(month == 9){
        days = 30;
        monthout = "September";
        out = "There are " + days + " days in " + monthout;
    }else if(month == 10){
        days = 31;
        monthout = "October";
        out = "There are " + days + " days in " + monthout;
    }else if(month == 11){
        days = 30;
        monthout = "November";
        out = "There are " + days + " days in " + monthout;
    }else if(month == 12){
        days = 31;
        monthout = "December";
        out = "There are " + days + " days in " + monthout;
    }else if(month > 12){
        out = "Your month input was not valid. Please try again.";
    }

    System.out.println(out);
}

}

Answer 1

你几乎可以用一对这样的数组替换整个if语句：

int dayCount[] = new int[] {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
String monthName[] = new String[] {"January", "February", ...};

掌握这两个数组后，您可以这样做：

// February is the only month that needs special handling
if (month == 2) {
    // Do your special handling of leap year etc...
} else if (month >= 1 && month <= 12) {
    // All other valid months go here. Since Java arrays are zero-based,
    // we subtract 1 from the month number
    days = dayCount[month-1];
    monthout = monthName[month-1];
} else {
    // Put handling of invalid month here
}
out = "There are " + days + " days in " + monthout;

Answer 2

switch(month) {
    case 1:
        // stuff
        break;
    case 2:
        // etc.....

如果你要这样做，你绝对应该使用enum而不仅仅是代表几个月的整数......

Answer 3

您可以使用switch-case语句。避免使用if-else

switch(month) {
    case 1:
        days = 31;
        monthout = "January";
        out = "There are " + days + " days in " + monthout;
        break;
    case 2:
        // Add stuff
         break;
    default:
        break;
}

Answer 4

开关：

switch (month)
{
    case 1:
        // ... stuff here
        break;
    case 2:
        // ... stuff here
        break;
    // ... more cases
    default: // no case above matched what the month was
        // .... handle default case
};

Answer 5

使用switch语句而不是其他许多if-if。它更容易阅读，修改和中断工作比否则更快 - 如果

case 1:
//code
break;

Answer 6

我认为你应该使用Map来避免所有这些if（或转换）情况。你的代码的主要问题是你需要复制很多代码。

private static Map<Integer, Integer> monthDays = new HashMap<>();

static {
    monthDays.put(1, 31);
    monthDays.put(2, 28);
    ...
}

private static int getMonthDays(int month) {
    if (month == 2) {
        // handle special case with Februar
    }
    return monthDays.get(month);
}

public static void main(String[] args) {
   ...    
   if (month >= 1 && month <= 12) {
       monthout = getMonthDays(month);
       ...
       out = "There are " + days + " days in " + monthout;
   } else {
       out = "Your month input was not valid. Please try again.";
   }
   System.out.println(out);
}

Answer 7

switch-case并不是更好。如果有超过3-4个if-else或switch条件，请考虑使用其他方式执行此操作，如命令或策略模式等。

例如，创建一个动作地图，如果条件设置并执行您想要的操作。示例代码如下。这只是示例代码让我知道，以防您需要进一步详细说明任何部分：

public void initMap(){
         Map<Integer, MonthData> monthDataMap = new HashMap<Integer,MonthData>();
         monthDataMap.put(1,new JanData());
         monthDataMap.put(2,new FebData());

     }

    interface MonthData {
        public String getMonth();
        public int getDays();
        public String getOut();
    }

    class JanData  implements MonthData{
        private String month ="January";
        private int days = 30;
        private String out =  "There are " + days + " days in " + month;

        @Override
        public String getMonth() {
            return month;
        }

        @Override
        public int getDays() {
            return days;
        }

        @Override
        public String getOut() {
            return out;
        }
    }


    class FebData {
        private String month ="February";
        private int days = 28;
        private String out =  "There are " + days + " days in " + month;
    }

    ....

形成这个if语句的更好方法是什么？

7 个答案: