Can't figure out how to change a character in string from upper to lower & vice versa

[sselasky1]

Hello, my name is Shane and I can't figure out how to take a string and convert each character from uppercase to lowercase and vice versa. For example AbCdE would convert to aBcDe. I am using JTextFields to do this. I didn't paste the GUI code since I am not having an issue with that but if you need me to paste the whole program I will. Any suggestions will be appreciated. Thanks.

 public void actionPerformed(ActionEvent e)
      {
    	 //declare variable

    	 int length, i;
    	 String str;
             char ch;
        
             //get input from text field
         str = string1TF.getText();
       
        //loop through string by each character
         for (i = 0; i < str.length(); i++)
         {
               
              //get character at position i
        	 ch = str.charAt(i);
        	
              // determine if letter is uppercase or lowercase and replace with opposite letter
        	 if (ch == Character.toUpperCase(ch))
        		 str.replace(ch, Character.toLowerCase(ch));
        	 else 
            	//	 str.replace(ch, Character.toUpperCase(ch));
        		 
         }
         
             //show string in text field
        	string2TF.setText(str);

        }

[Fubarable]

Burn this into your brain: Strings are immutable -- meaning they can't be changed. Ever.

You're calling String#replace(...) method, but from the rule I mention above, you now know that this doesn't change the String that has the method called on it. No instead it returns a String with the changes made. If you want the original String variable to refer to this new String you have to assign it to do this. e.g.,

myString = myString.replace("a", "A");

[sselasky1]

Burn this into your brain: Strings are immutable -- meaning they can't be changed. Ever.

You're calling String#replace(...) method, but from the rule I mention above, you now know that this doesn't change the String that has the method called on it. No instead it returns a String with the changes made. If you want the original String variable to refer to this new String you have to assign it to do this. e.g.,

myString = myString.replace("a", "A");

Shane: Burned into my head. But what about if the string is AaA. How would I go about changing the string to aAa?

[Fubarable]

Shane: Burned into my head. But what about if the string is AaA. How would I go about changing the string to aAa?

My code was just an example. Please don't take it as a literal example. Use your powerful brain and the ideas we've given you and modify your code. I'll bet that you'll be able to figure it out. Please let us know though either way what happens.

[sselasky1]

My code was just an example. Please don't take it as a literal example. Use your powerful brain and the ideas we've given you and modify your code. I'll bet that you'll be able to figure it out. Please let us know though either way what happens.

shane: Got it. However, when I cycle loop through my string, all the letters in the string are converting all to uppercase or lowercase. Is this a result of what you said earlier?

          // loop through string
         for (i = 0; i < str.length(); i++)
         {
              //get char
        	 ch = str.charAt(i);
        	 
        	// check char if upper or lowercase and convert to opposite letter
        	 if (ch == Character.toUpperCase(ch))
        		str = str.replace(str.charAt(i), Character.toLowerCase(str.charAt(i)));
        	 else 
            	 str = str.replace(str.charAt(i), Character.toUpperCase(str.charAt(i)));
        		 
         }

[Fubarable]

You need to look at the String API to see just what replace does as it's doing a lot more than you think it's doing. Myself, I'd use a StringBuffer for this problem, not a String since it is mutable, and since it can be easily changed into a String via its toString() method.