CODEWITHSUNDEEP
javastring
logonin
logonin

Reputation: 103

Switching the first and last letter of a string in Java?

I have to write a method to switch the first and last letter of a string. For example the string "java" would become "aavj".

Here is what I have so far:

import javax.swing.JOptionPane;

public class printTest {
    public static void main(String[] args) {
        String password;
        password = JOptionPane.showInputDialog("Please input your password");
        int length = password.length();
        String firstChar = password.substring(0, 1);
        String lastChar = password.substring(length - 1);

        password = lastChar + password + firstChar;
        JOptionPane.showMessageDialog(null, password);
    }
}

With that code I get the following output "ajavaj" when I input "java", so how can I fix this? I need to switch the first two letters and still have the middle of the string. What should I do?

Upvotes: 4

Views: 3041

Answers (6)

Gary
Gary

Reputation: 13912

Not much different than the other answers, but another way:

password = password.charAt(password.length() - 1)
           + password.substring(1, password.length() - 1)
           + password.charAt(0);

Upvotes: 1

Jake H.
Jake H.

Reputation: 969

You need to substring password on this line:

password = lastChar + password.substring(1, length-1) + firstChar;

Upvotes: 7

Baronz
Baronz

Reputation: 677

The way you were getting the first character was correct, but not the middle or last. Here's a solution showing all three cases:

  String password = "123456789";
  int length = password.length();

  String firstChar = password.substring(0, 1);
  String middle = password.substring(1, length - 1);
  String lastChar = password.substring(length - 1, length);

  password = lastChar + " " + middle + " " + firstChar;
  System.out.println(password);

This will print:

9 2345678 1

Upvotes: 1

ninja.coder
ninja.coder

Reputation: 9648

By doing password = lastChar + password + firstChar; you are concatenating the original password String with the two other Strings i.e. lastChar & firstChar. By doing this you will actually get a new String with lastChar and firstChar appended and not swapped.

Also, Strings are immutable and every time you are trying to manipulate it, you are ending up creating a new String. You should use char array instead to avoid this problem.

Try this piece of code:

import javax.swing.JOptionPane;
public class printTest
{
     public static void main(String[] args)
     {
          /* Capture Password */
          String password = JOptionPane.showInputDialog("Please input your password");
          char[] pass = password.toCharArray();

          /* Swap Logic */
          char temp = pass[0];
          pass[0] = pass[pass.length - 1];
          pass[pass.length - 1] = temp;

          /* Show MessageDialog */
          JOptionPane.showMessageDialog(null, new String(pass));
     }
}

Upvotes: 3

Robbe Dillen
Robbe Dillen

Reputation: 23

I think this should do the trick: 

import javax.swing.JOptionPane;
    public class printTest
    {
     public static void main(String[] args)
     {
     String password;
    password = JOptionPane.showInputDialog("Please input your password");
    int length = password.length();
      String password_changed = password.substring(1, password.length() - 1);
      String firstChar = password.substring(0,1);
      String lastChar = password.substring(length - 1);



      password =  lastChar +  password_changed + firstChar;
      JOptionPane.showMessageDialog(null, password);
     }
    }

You make an extra string (in this example password_changed) in wich you delete the first and last letter of the password variable. And you can use that new variable to change the password variable at the end.

Upvotes: 2

Jorel Amthor
Jorel Amthor

Reputation: 1294

char c[] = password.toCharArray();
char temp = c[0]
c[0] = c[password.length-1];
c[password.length-1] = temp;

There you go, swapping those two letters. The c[0] will be your first letter, you store it in a temp variable, then modify the value of c[0] ( your first letter ) with the one in c[password.length-1] ( your last letter ) and then modify this value with the one store in the temp variable

Upvotes: 1

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