a
ab
abc
abcd
abcde
abcdef
abcdefg
abcdefgh
abcdefghi
abcdefghij
abcdefghijk
abcdefghijkl
abcdefghijklm
abcdefghijklmn
abcdefghijklmno
abcdefghijklmnop
abcdefghijklmnopq
abcdefghijklmnopqr
abcdefghijklmnopqrs
abcdefghijklmnopqrst
abcdefghijklmnopqrstu
abcdefghijklmnopqrstuv
abcdefghijklmnopqrstuvw
abcdefghijklmnopqrstuvwx
abcdefghijklmnopqrstuvwxy
abcdefghijklmnopqrstuvwxyz

char ch;
for( ch = 'a' ; ch <= 'z' ; ch++ )
    System.out.println(ch);
System.out.println("Purple Loop");

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

for (int i = 1; i <= 26; i++) {
    char ch = 'a';
    for (int j = 0; j < i; j++, ch++)
        System.out.print(ch);
    System.out.println();
}