java - 如何使用字符串作为输入值？

Question

我的任务是制作一个程序，允许用户输入他们的出生日期，然后它将输出他们的十二生肖和星座。该程序认为月份是未声明的变量，但我试图使它们的值与变量“月份”相同。

这是代码，

<小时/>

int  day, year;
String month;

System.out.println("Enter the month you were born.");
month=in.nextLine();
System.out.println("Enter day you were born.");
day=in.nextInt();
System.out.println("Enter the year you were born."); 
year=in.nextInt(); 

if (month==January && day <=20)
    System.out.println("You are a Capricorn.");
if (month==January && day > 20)
    System.out.println ("You are an Aquarius.");
if (month==February && day <= 19)
    System.out.println ("You are an Aquarius.");
if (month==February && day >19)
    System.out.println ("You are a Pisces.");
if (month==March && day <= 20)
    System.out.println ("You are a Pisces.");
if (month==March && day > 20)
    System.out.println ("You are an Aries.");
if (month==April && day <= 20)
    System.out.println ("You are an Aries.");
if (month==April && day >20)
    System.out.println ("You are a Taurus.");
if (month==May && day <= 21)
    System.out.println ("You are a Taurus.");
if (month==May && day > 21)
    System.out.println ("You are a Gemini.");
if (month==June && day <= 21)
    System.out.println ("You are a Gemini.");
if (month==June && day >21)
    System.out.println ("You are a Cancer.");
if (month==July && day <=22)
    System.out.println ("You are a Cancer.");
if (month==July && day >22)
    System.out.println ("You are a Leo.");
if (month==August && day <=22)
    System.out.println ("You are a Leo.");
if (month==August && day >22)
    System.out.println ("You are a Virgo.");
if (month==September && day <=23)
    System.out.println ("You are a Virgo.");
if (month==September && day >23)
    System.out.println ("You are a Libra.");
if (month==October && day <=23)
    System.out.println ("You are a Libra.");
if (month==October && day >23)
    System.out.println ("You are a Scorpio.");
if (month==November && day <=22)
    System.out.println ("You are a Scorpio.");
if (month==November && day >22)
    System.out.println ("You are a Sagittarius.");
if (month==December && day <=21)
    System.out.println ("You are a Sagittarius.");
else
    System.out.println ("You are a Capricorn.");

Answer 1

您需要通过在月份字符串中添加双引号来创建月份字符串:

if (month.equals("January") && day <=20)
System.out.println("You are a Capricorn.");

意识到用户必须准确输入“January”，因此“january”不起作用。要实现此目的，请确保使用 toLower 函数。您还可以使用equalsIgnoreCase()。

每个月都遵循相同的模式。任何时候使用字符串文字时，它都需要位于 "" 中。另外，如果您要比较字符串，则需要使用 equals()，如上所示。

正如 Luiggi 在下面的评论中指出的那样，这样做更有意义:

 if ("January".equals(month) && day <=20)

这将避免可能出现的NullPointerException错误。