for loop, iteration through alphabet? java

Question

I can iterate through the alphabet, but I'm trying to keep the last iteration and add on the next letter. this is my code.

for(char alphabet = 'a'; alphabet <='z'; alphabet ++ )
        {

            System.out.println(alphabet);
        }

I want it to print out something that looks like this.

a

ab

abc

abcd

abcde..... and so forth. How is this possible?

Answer 1

I'd suggest using a StringBuilder:

// Using StringBuilder
StringBuilder buf = new StringBuilder();
for (char c = 'a'; c <= 'z'; c++)
    System.out.println(buf.append(c).toString());

You could also do it slightly faster by using a char[], however StringBuilder is more obvious and easier to use:

// Using char[]
char[] arr = new char[26];
for (int i = 0; i < 26; i++) {
    arr[i] = (char)('a' + i);
    System.out.println(new String(arr, 0, i + 1));
}

Alternatives that you shouldn't use:

• StringBuffer: Same as StringBuilder, but synchronized, so slower.
• s = s.concat(new String(c)): Allocates 2 Strings per iteration, instead of only 1.
• s += c: Internally += is compiled to s = new StringBuilder().append(s).append(c).toString(), so horrendously slow with exponential response times.

Answer 2

You need to add the char alphabet to a string.

String output = "";

for(char alphabet = 'a'; alphabet <='z'; alphabet++ )
    {
        output += alphabet;
        System.out.println(output);
    }

This should work for you ;)

Answer 3

I will go with StringBuffer or StringBuilder. Something like:

StringBuffer

StringBuffer sb = new StringBuffer();
for (char alphabet = 'a'; alphabet <= 'z'; alphabet++) {
    sb.append(alphabet);
    System.out.println(sb.toString());
}

StringBuilder

StringBuilder sb = new StringBuilder();
for (char alphabet = 'a'; alphabet <= 'z'; alphabet++) {
    sb.append(alphabet);
    System.out.println(sb.toString());
}

String vs StringBuffer vs StringBuilder:

String: It is immutable, so when you do any modification in the string, it will create new instance and will eatup memory too fast.

StringBuffer: You can use it to create dynamic String and at the sametime only 1 object will be there so very less memory will be used. It is synchronized (which makes it slower).

StringBuilder: It is similar to StringBuffer. The olny difference is: it not synchronized and hence faster.

So, better choice would be StringBuilder. Read more.

Using Java 8

StringBuilder sb = new StringBuilder();

IntStream.range('a', 'z').forEach(i -> {
    sb.append((char) i);
    System.out.println(sb.toString());
});