Question

I am learning Java.

I am supposed to write a program that converts all uppercase letters to lowercase and all lowercase to uppercase. It said in the book I just need to subtract 32 from uppercase and add 32 to lowercase.

Here is my code…

class Caseconv {
    public static void main(String args[])
        throws java.io.IOException {
            char ch;

            do {
            ch = (char) System.in.read();

            if (ch >= 97 & ch <= 122) ch = ch - 32;
            if (ch >= 65 & ch <= 90) ch = ch + 32;
            System.out.print(ch);
            } while (ch != '\n');
        }
}

But the compiler doesn’t want to do this, I get this error.

Caseconv.java:13: error: possible loss of precision
            if (ch >= 97 & ch <= 122) ch = ch - 32;
                                              ^
  required: char
  found:    int
Caseconv.java:14: error: possible loss of precision
            if (ch >= 65 & ch <= 90) ch = ch + 32;
                                             ^
  required: char
  found:    int
2 errors

What am I supposed to be doing to subtract from the char?

Answer 1

You need to add a type cast to convert the result of the expression to char. For example.

ch = (char)(ch + 32)

Notes:

1. The reason this is necessary is because 32 is an int literal, and the addition of a char and an int is performed using int arithmetic, and gives an int result.

2. Assigning an int to a char potentially results in truncation. Adding the type cast effectively says to the compiler: “Yes. I know. It is OK. Just do it.”

3. The parentheses around the + subexpression are necessary because type-cast has higher precedence than +. If you leave them out, the type-cast makes no difference because it “casts” a char to a char.