package Progress;
import java.util.Collection;

/**
 * Expandable list type that will be displayed in the left side bar.
 */
public abstract class List{
    private String name;
    private Collection<String> topics;
    
    /**
     * Adds a link to the list.
     *

      pre:
        // The String topic must not equal null.
        topic != null
 
          &&

        // The String topic must not be empty.
        !topic.isEmpty();
   
      post:
        // The String topic is now in this.topics.
        topics'.contains(topic);
     *
     */
    public void addToList(String topic) {
	boolean b = !topic.isEmpty();
	topics.contains(topic);
    }
    /* SPEST PROBLEM:
       The checker outputs
   Invalid invocation: isEmpty() at line: 22  at character: 15
   Invalid invocation: contains(antlr.TestGenerator$arguments_return@282492ec) at line: 26  at character: 16

       but javac seems to be OK with these expressions.

     */
}