英文:
Java - !String.equals("abc") returning TRUE when it should be FALSE
问题
我正在为学校解决这个问题（请忽略您可能看到的任何其他错误，我仍在努力解决中）。我在我的 while 循环中遇到了问题。
我正在努力添加一个检查，以防用户没有输入 c 或 f，要求他们重新输入，直到他们输入这两个字母之一。
然而，在调试时，我发现函数在我的语句中忽略了 !，并且当 units 的值为 c 时返回 TRUE。
public class TempConvert {
// 转换从华氏温度到摄氏温度
static int convToCelsius(int tempF) {
int tempC = (tempF - 32) * 5 / 9;
return tempC;
}
// 转换从摄氏温度到华氏温度
static int convToFahrenheit(int tempC){
int tempF = (tempC * 9 / 5) + 32;
return tempF;
}
public static void main(String[] args){
int temp; // 用户指定的温度
int convTemp; // 转换后的温度变量
String units; // 用户指定的单位
System.out.println("This program converts Temperatures from Fahrenheit to Celsius and vice versa.");
System.out.print("Please enter your temperature: ");
temp = TextIO.getlnInt();
System.out.print("Please enter the units (F/C):");
units = TextIO.getlnWord().toLowerCase();
while (!units.equals("c") || !units.equals("f")){
System.out.print("Please enter F for Fahrenheit or C for Celsius: ");
units = TextIO.getlnWord();
}
if (units.equals("c")){
convTemp = convToFahrenheit(temp);
System.out.printf("A temperature of %d degrees Fahrenheit is equivalent to %d degrees Celsius", temp, convTemp);
}
else if (units.equals("f")){
convTemp = convToCelsius(temp);
System.out.printf("A temperature of %d degrees Celsius is equivalent to %d degrees Fahrenheit", temp, convTemp);
}
} // end main
} // end class
英文:
I am working on this problem for school (please ignore any other errors you may see, I'm still working through it). I am getting stuck on my while loop.
I'm working to add in a check for if the user doesn't input a c or f to re-ask them until they input one of those two letters.
However, as I debug it I am finding the function is ignoring the ! in my statement and returning TRUE when the value for units is c.
public class TempConvert {
// converts from fahrenheit to celsius
static int convToCelsius(int tempF) {
int tempC = (tempF - 32) * 5 / 9;
return tempC;
}
// converts from celsius to fahrenheit
static int convToFahrenheit(int tempC){
int tempF = (tempC * 9 / 5) + 32;
return tempF;
}
public static void main(String[] args){
int temp; // user specified temp
int convTemp; // var for converted temp
String units; // user specified unit
System.out.println("This program converts Temperatures from Fahrenheit to Celsius and vice versa.");
System.out.print("Please enter your temperature: ");
temp = TextIO.getlnInt();
System.out.print("Please enter the units (F/C):");
units = TextIO.getlnWord().toLowerCase();
while (!units.equals("c") || !units.equals("f")){
System.out.print("Please enter F for Fahrenheit or C for Celsius: ");
units = TextIO.getlnWord();
}
if (units.equals("c")){
convTemp = convToFahrenheit(temp);
System.out.printf("A temperature of %d degrees Fahrenheit is equivalent to %d degrees Celsius", temp, convTemp);
}
else if (units.equals("f")){
convTemp = convToCelsius(temp);
System.out.printf("A temperature of %d degrees Celsius is equivalent to %d degrees Fahrenheit", temp, convTemp);
}
} // end main
} // end class
答案1
得分: 3
!units.equals("c") || !units.equals("f")
仔细阅读并思考一下。上述内容在无论 `units` 保存了什么值时都 __始终__ 为真。
假设它保存的是 `"c"`。
我们来代入计算：
!units.equals("c") || !units.equals("f")
!true || !false
false || true
true
我很确定你可能是想要的是 `!units.equals("c") && !units.equals("f")`，或者可能是 `!(units.equals("c") || units.equals("f"))`，它们实际上是等价的。
英文:
> !units.equals("c") || !units.equals("f")
Just go through it and think about it. The above is always true, regardless of what units holds.
Let's say it holds "c".
let's fill it in:
!units.equals("c") || !units.equals("f")
!true || !false
false || true
true
I'm pretty sure you meant !units.equals("c") && !units.equals("f") instead, or maybe !(units.equals("c") || units.equals("f")) which boils down to the same thing.
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