import com.intellij.util.containers.HashSet; import java.util.Set; import java.util.HashSet; public class Main { public static void main(String[] args) { Runnable runnable = new Runnable() { @Override public void run() { Set<String> test = new HashSet<String>(); if (test.contains("AA")) { System.out.println("AAAA!"); } } }; runnable.run(); } }