Java程序将大写和小写反转

Question

I have to write a program to input a String str and change the upper case to lower case and vice versa. For example:

input: "abCD"

output: "ABcd"

this is what I've got:

l-is the length of the string

for(int b=0;b < l;b++)

             {

               char let=str.charAt(b);

               if(let>97 && let<122)

               {char nlet=let-32;

               System.out.print(nlet);

            }
            else if(let>65 && let<90)
             { char t=let+32;
              System.out.print(t);
            }
           }
           break; 
        }

the error coming for this line:" char nlet=let-32; " is: required:char;found:int;

how do i fix this?

Answer 1

The issue is that 32 is an integer, and let is a char. Java will implicity convert the let value to an int when it encounters let-32 and the result is the int value (for 'a') 96 or whatever.

You need to cast the result back to char:

(char)(let+32)

Answer 2

Try to use the below updated for loop:

 for(int b=0;b < l;b++)

             {

               char let=str.charAt(b);

               if (Character.isLowerCase(let))
               {
                   char nlet=Character.toUpperCase(let);

               System.out.print(nlet);

              } else if(Character.isUpperCase(let))
             { char t=Character.toLowerCase(let);
              System.out.print(t);
            }
           }
           break; 
        }

Answer 3

Without any other classes (like Character for apparently you can't use it), you need to cast into char :

for(int b=0;b < l;b++)
{
    char let=str.charAt(b);

    if(let>97 && let<122)
    {
        char nlet=(char) let-32;
        System.out.print(nlet);
    }
    else if(let>65 && let<90)
    {
        char t=(char)let+32;
        System.out.print(t);
    }
}

Your compiler told you the answer here :

required:char;found:int

It means your operation, here it is variable assignation has a wrong argument. When you have

 char nlet = xxx

The compiler expects the xxx to be castable into char . Here you give it a int value with let-32 or let+32 . So here you need to cast into char or use a function that output a char from an int ; that's where you see all the people here telling you to use Character class that gives you all helper functions to do your homework (which is also way better than manually add/sub 32)

Careful, sometime you can see something like String str = "A string from int: " + 2000 This means your compiler will automatically cast the 2000 into "2000" because the + operation for a String takes 2 string arguments.

Answer 4

The Problem is with your let-32; it will return an integer so you need to implicitly cast it to a char variable.

Change your code to char nlet=(char) (let-32);

Also there is one more problem in your if condition you program will not give the correct output as your are not checking for the alphabets 'a' and 'z'.Change your if -else to check for the boundary conditions.

if(let>=97 && let<=122)
{
}else (let>=65 && let<=90){ 
}