Question

Possible Duplicate:
How do I compare strings in Java?

I’m fairly new to Java and to practice I’m trying to create a hexadecimal to decimal number converter since I’ve successfully managed to make a binary to decimal converter.

The problem I’m having is basically comparing a given character of in a String with another string. This is how I define the current character that is to be compared:

String current = String.valueOf(hex.charAt(i));

This is how I try to compare the character:

else if (current == "b") 
   dec += 10 * (int)Math.pow(16, power);

When I try to run the code by entering just numbers e.g. 12, it works but when I try to use a ‘b’, I get a weird error. Here is the entire result of running the program:

run:
Hello! Please enter a hexadecimal number.
2b
For input string: "b" // this is the weird error I don't understand
BUILD SUCCESSFUL (total time: 1 second)

Here is an example of successfully running the program with just a number conversion:

run:
Hello! Please enter a hexadecimal number.
22
22 in decimal: 34 // works fine
BUILD SUCCESSFUL (total time: 3 seconds)

Any help with this would be appreciated, thanks.

Edit: I think it will be useful if I put the entire method here.

Edit 2: SOLVED! I don’t know who’s answer that I should accept though because they were all so good and helpful. So conflicted.

for (int i = hex.length() - 1; i >= 0; i--) {
        String lowercaseHex = hex.toLowerCase();
        char currentChar = lowercaseHex.charAt(i);

        // if numbers, multiply them by 16^current power
        if (currentChar == '0' || 
                currentChar == '1' || 
                currentChar == '2' || 
                currentChar == '3' || 
                currentChar == '4' || 
                currentChar == '5' || 
                currentChar == '6' || 
                currentChar == '7' || 
                currentChar == '8' || 
                currentChar == '9')
            // turn each number into a string then an integer, then multiply it by
            // 16 to the current power.
            dec += Integer.valueOf(String.valueOf((currentChar))) * (int)Math.pow(16, power);

        // check for letters and multiply their values by 16^current power
        else if (currentChar == 'a') 
            dec += 10 * (int)Math.pow(16, power);
        else if (currentChar == 'b') 
            dec += 11 * (int)Math.pow(16, power);
        else if (currentChar == 'c') 
            dec += 12 * (int)Math.pow(16, power);
        else if (currentChar == 'd') 
            dec += 13 * (int)Math.pow(16, power);
        else if (currentChar == 'e') 
            dec += 14 * (int)Math.pow(16, power);
        else if (currentChar == 'f') 
            dec += 15 * (int)Math.pow(16, power);
        else
            return 0;
        power++; // increment the power
    }

    return dec; // return decimal form
}

Answer 1

Try initializing a char to the char value returned by charAt()

char current = hex.charAt(i);

Then in your conditional use the literal char:

else if (current == 'b') 

Since char is a primitive you can compare it using the == operator. In the former code you were comparing a String using ==, since a String is an Object the code is checking to see if they are the same Object not if they have the same value as the String.equals() method would.