Using a BitMap, I'm assuming you meant case insenstive.
Update: Solution by Thomas is more efficient, than the following. :) Use that one.
//
String test = "abcdefeghjiklmnopqrstuvwxyz";
BitSet alpha = new BitSet(26);
for(char ch : test.toUpperCase().toCharArray())
if(Character.isLetter(ch))
alpha.set(ch - 65);
System.out.println(alpha.cardinality() == 26);
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