import java.util.*; // gerekli import

ArrayList<Character> list = new ArrayList<Character>();
list.add('a');
list.add('a');
list.add('a');
list.add('a');
list.add('b');
list.add('b');
System.out.println("a" + " karakteri " + Collections.frequency(list, 'a') + " tane..");
System.out.println("b" + " karakteri " + Collections.frequency(list, 'b') + " tane..");