/* Expressões regulares com Java Patterns
   http://pt.stackoverflow.com/q/186142/53463 */
 
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		final String regex = "^[^ab]*+(?=(?:[^b]*b){2})(?:[^a]*a){2}[^a]*$";
 
		String[] exemplos = new String[] { 
			"---aabb+++","---bbaa+++","---abab+++","---baba+++",
			"---babba++","---bbbbbaa","ababbb++++","ccabcab+++",
			"----bcdbaa","-ababd++++","bbbaabbbbb","bbbabbbbbb",
			"bbbaaabbbb","baaaaaaaaa","abbbbbbbbb","ccacbcacbc"
		};
 
 
		final Pattern pattern = Pattern.compile(regex);
 
		for (String palavra : exemplos) {
			Matcher matcher = pattern.matcher(palavra);
 
			if (matcher.find()) {
			    System.out.println(palavra + " ✔️");
			} else {
			    System.out.println(palavra + " ✖️️");
			}
		}
	}
}

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