In your case the following (although not optimal) code can serve as a guidance
public class Main {
public static void main(final String[] args) throws Exception {
final String tagged = "World_NN Big_RBS old_RB stupid_JJ";
int nouns = 0;
int adjectives = 0;
int adverbs = 0;
final String[] tokens = tagged.split(" ");
for (final String token : tokens) {
final int lastUnderscoreIndex = token.lastIndexOf("_");
final String realToken = token.substring(lastUnderscoreIndex + 1);
if ("NN".equals(realToken)) {
nouns++;
}
if ("JJ".equals(realToken)) {
adjectives++;
}
if ("RB".equals(realToken) || "RBS".equals(realToken)) {
adverbs++;
}
}
System.out.println(String.format("Nouns: %d Adjectives: %d, Adverbs: %d", nouns, adjectives, adverbs));
}
}
And a fiddle for it.