for loop to while loop

Question

I am using a for loop to print the backwards alphabet in uppercase but I would like to know how to do the same thing with a while loop, which I am not very good with.

String alphabet = "abcdefghijklmnopqstuvwxyz";      
int x = 0;

for(x = alphabet.length() - 1; x > -1; x--) {
  System.out.print(alphabet.charAt(x));
  System.out.print(alphabet.toUpperCase());                 
}

I also need to terminate it when it reaches A. think it's something like this, but I don't know how to make it loop backwards. I'd really appreciate your help!

while(alphabet.length() < 26) {
  System.out.print(alphabet.charAt(x));  
  System.out.print(alphabet.toUpperCase());     
  if(x == A) {
    break;
  }     
}

"for(A; B; C) { body; }" is equivalent to "A; while(B) { body; C; }" — ignis
– ignis, Commented Oct 27, 2012 at 16:50
The while(alphabet.length()<26) {} loop will never terminate. — antiguru
– antiguru, Commented Oct 27, 2012 at 16:51
... And there's no need to iterate over a string (as long as you want the english alphabet): start with char c = 'Z', and while c >='A', print and then decrement c. You can do it in a single 'for' statement. — ignis
– ignis, Commented Oct 27, 2012 at 16:56

Rohit Jain · Accepted Answer · 2012-10-27 17:10:46Z

4

for (initialization; condition; increment) {

}

is same as:

{
    initialization;
    while(condition) {
       // body
       increment;
    }
}

The outer block creates a block scope for the initialized parameter, that we get in a for loop also. But, if you are declaring your for-loop variable outside the loop, then you can omit that outer block.

Now you can map your for loop to the while loop.

edited Oct 27, 2012 at 17:10

answered Oct 27, 2012 at 16:51

Rohit Jain

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4 Comments

Rohit Jain Over a year ago

@user1707517. Yeah. both the loops work exactly in the same way with some modification in structure. :)

Pshemo Over a year ago

I would also place second code in outer block like { initialization; while(condition) { body; increment;} } since variables declared in initialization wont be accessible after that block.

Rohit Jain Over a year ago

@Pshemo. Ah! true. nice catch. Will add it. :) +1 on it.

Daniel Fischer Over a year ago

The translation is not so simple if there are continues in the loop. In the for loop, a continue jumps to the increment code, in the while loop that would be skipped. Not sure what the best way to treat that is, without goto.

Jagger · Accepted Answer · 2012-10-27 17:14:35Z

2

There is a much simpler way to reverse a string in Java.

public class StringReversalExample {
    public static void main(String[] args) {
      String alphabet = "abcdefghijklmnopqstuvwxyz";
      String reversedString = new StringBuilder(alphabet).reverse().toString();
      System.out.println(reversedString);
    }
}

edited Oct 27, 2012 at 17:14

answered Oct 27, 2012 at 16:58

Jagger

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Comments

ioseb · Accepted Answer · 2012-10-27 17:19:22Z

2

Try this:

public static void main(String[] args) {
  char[] alphabet =  "abcdefghijklmnopqstuvwxyz".toCharArray();
  int index = alphabet.length - 1;

  while (index >= 0) {
    System.out.println(alphabet[index--]);
  }
}

This is a most efficient solution with minimal memory overhead.

edited Oct 27, 2012 at 17:19

answered Oct 27, 2012 at 16:51

ioseb

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Comments

ersran9 · Accepted Answer · 2012-10-27 16:55:08Z

0

x = alphabet.length() - 1;
while( x > -1 )
    {
        System.out.print(  alphabet.charAt( x ));  
        System.out.print( alphabet.toUpperCase() );
        x--;
    }

edited Oct 27, 2012 at 16:55

ersran9

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answered Oct 27, 2012 at 16:51

Ravindra Bagale

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