Java - Why can't I use charAt() to see if a char equals another?

问题

I want to see if a character in my string equals a certain other char value but I do not know what the char in the string is so I have used this:

if ( fieldNames.charAt(4) == "f" )

But I get the error:

"Operator '==' cannot be applied to 'char', 'jav.lang.String'"

But "g" == "h" seems to work and I know you can use '==' with char types.

Is there another way to do this correctly? Thanks!

回答1:

if ( fieldNames.charAt(4) == 'f' )

because "f" is a String and fieldNames.charAt(4) is a char. you should use 'f' for check char

"g" == "h" works because both g and h are Strings

and you shouldn't use "g" == "h" you should use "g".equals("h") instead . you can use == for primitive data types like char,int,boolean....etc.but for the objects like String it's really different. To know why read this

but you can use also

'g' == 'h' 

you should wrap Strings by double quotation and char by single quotation

String s="g";

char c='g';

but char can only have one character but String can have more than one

String s="gg";  valid

char c='gg';  not valid

回答2:

I was having the same problem, but I was able to solve it using:

if (str.substring(0,1).equals("x") )

the substring can be used in a loop str.substring(i, i + 1)

charAt(i).equals('x') will not work together

回答3:

This works:

if (String(fieldNames.charAt(4)) == "f")

来源：https://stackoverflow.com/questions/26688990/java-why-cant-i-use-charat-to-see-if-a-char-equals-another