Problem with char/string representation

I have this code for Caesar cipher implementation, which works fine, but when I adapt it for my code it is not working.

import java.io.*;  //This is the java input output library

public class Caesar
{

/*This is the main program.*/
        public static void main(String[] args) throws IOException
        {
                BufferedReader in =new BufferedReader(new InputStreamReader(System.in));  //reader for keyboard
                int key=22; //I have chosen 22 to be my key value but you can change this to any value between 0 and 25
                System.out.println("Enter your plaintext: ");
                String s=in.readLine();   // string s now contains the plaintext
                System.out.println();
                System.out.println();
                for(int i=0;i<s.length();i++)  //we look at the plaintext one character at a time
                {
                        int current=s.charAt(i);   //current holds the character as an int value - the ASCII value
                        if(current>64 && current<91)  //if the character is an upper case letter
                        {
                                current=current+key;  //add the key value onto the ASCII value
                                if(current>90) current=current-26;  //if we've come off the end of the alphabet then we loop
                        }                                                                               //back around by subtracting 26.
                        else if(current>96 && current<123) //if the character is a lower case letter
                        {
                                current=current+key;
                                if(current>122)current=current-26;
                        }
                        System.out.print((char)(current));  //now we print out the encrypted character or if the character
                }System.out.println();                      //was not a letter then we print the original character.
        }
}

Here is my class:

public class CipherGenerator extends JFrame {

public static void main(String[] args) {}
private JTextArea plainTextArea = new JTextArea();
private JTextArea chipherTextArea = new JTextArea();
private JComboBox chipher = new JComboBox();
String []chipherList = {"Cezar, Vigenere, Playfair, DES"};
private JPanel groupBoxDecryption = new JPanel();

chipherListCombo.addItemListener(new ItemListener(){
		      public void itemStateChanged(ItemEvent ie){
		        String str = (String)chipherListCombo.getSelectedItem();

add(groupBoxEncryption);
		groupBoxEncryption.setLayout(null);
		groupBoxEncryption.setVisible(true);
		groupBoxEncryption.setBounds(30, 40, 700, 290);
		groupBoxEncryption.setBorder(BorderFactory.createTitledBorder(null, "Encryption", 
TitledBorder.DEFAULT_JUSTIFICATION, TitledBorder.DEFAULT_POSITION, 
new Font("Dialog", Font.BOLD, 12), new Color(51, 51, 51)));
		
// Add TextArea plainText to the Panel
		groupBoxEncryption.add(plainTextArea);
		plainTextArea.setBounds(100, 30, 250, 100);
		plainTextArea.setVisible(true);
		plainTextArea.setBorder(BorderFactory.createLineBorder(Color.gray));
		plainTextArea.setLineWrap(true);

groupBoxEncryption.add(chipherListCombo);		
		chipherListCombo.setBounds(100, 220, 250, 21);
		chipherListCombo.setVisible(true);
		chipherListCombo.addItem("Choose cipher algorithm..");

JButton buttonEncryption = new JButton("Encryption");
			groupBoxEncryption.add(buttonEncryption);
			buttonEncryption.setVisible(true);
			buttonEncryption.setBounds(100, 250, 90, 24);
			buttonEncryption.setFont(new Font("Arial", Font.PLAIN, 12));
			
			buttonEncryption.addActionListener(new ActionListener(){
				public void actionPerformed(ActionEvent e){
					String str = (String)chipherListCombo.getSelectedItem();

chipherListCombo.addItem("Caesar");
		chipherListCombo.addItem("Vigenere");
		chipherListCombo.addItem("Playfair");
		chipherListCombo.addItem("DES");

if(str == "Caesar"){
         int key=3; 
         String plainText = plainTextArea.getText();
			               
	  for(int i = 0; i < plainText.length(); i++)  //we look at the plaintext one character at a time
	  {
		current = plainText.charAt(i);   //current holds the character as an int value -
                                                                                             // the ASCII value
			                       
                         if(current > 64 && current < 91)  //if the character is an upper case letter
			   {
			             current = current + key;  //add the key value onto the ASCII value
			              if(current > 90) 
			                      current=current-26;  //if we've come off the end of the alphabet then we loop
			                        }                                                            //back around by subtracting 26.
			                        else if(current > 96 && current < 123) //if the character is a lower case letter
			                        {                
			                        	 current = current + key;
			                        	
			                        	 if(current > 122)
			                        		 current=current-26;
			                        }

// here is the problem, I get only last letter, not all of them,
// like it works with System.out.println in Caesar class
String chipher = String.valueOf((char) (current));
 chipherTextArea.setText(chipher);    
}

I suppose it is a problem with String conversion, it is showing only the last character,
but why it is working in Console, then ? How do I make it to work in TextArea, as well ?

Could someone please help me with this ? Thank You!

You're just getting the current character--you're not building a string containing the built-up ciphertext.

But how than this works in first class ? And how to build string ?

Because in the first one you're printing out each character. In the last one you just get the current character.

I think if you're writing Swing apps but don't know how to build a string the learning is happening backwards... Maybe search the web for "java string concatenation".

Thanks for quick response!

I know how to do concatenation.

I was just asking for opinion how to do it maybe on another way in this case.
Thanks, anyway.

Well, you're trying to build a string character-by-character. Since Java Strings are immutable, there'd be the overhead of a new string *somewhere* in the process.

Ok, I see.

But is there any way to adapt this code written for console to work as I wanted for Swing ? Or it is not possible to work on this way ?
Some way to gather currents to string, or with type cast ?

You said you knew how to concatenate strings--so concatenate away!

Why are you using == to check Strings for equality?
Would the StringBuilder class help?

Hi Ritchie!

Thank You for reply!

I am using == because I am checking which item is selected in Combo box.
In Combo box I have a few types of encryption algorithms and one of them is Caesar.

I just read description about of String Builder class, and will give it try!

Nicol Green wrote:I am using == because I am checking which item is selected in Combo box.

No... in this code

you are comparing two strings. You aren't doing anything with items or combo boxes there.

When I was copying code from my project I made mistake,
it should go like this:

Now should be ok, if I understand good what you mean ?

Nope. You're still using the == operator to attempt to compare the contents of two strings. Don't do that. Use the equals() method of either of the two.

Now I see what you mean, it is beginning Java mistake..

Thanks!