小编Com*_*tix的帖子

TreeMap<String,ArrayList<String>> statesToPresidents = new TreeMap<String,ArrayList<String>>();
    TreeMap<String,String> reversedMap = new TreeMap<String,String>();
    TreeSet<String> presidentsWithoutStates = new TreeSet<String>();
    TreeSet<String>statesWithoutPresidents = new TreeSet<String>(); while (infile2.ready())
    {
        String president = infile2.readLine();
        if (reversedMap.containsKey(president)==false)
            presidentsWithoutStates.add(president);
    }

    infile2.close();

    System.out.println( "\nThese presidents were born before the states were formed:\n");  // DO NOT REMOVE OR MODIFY

    // YOUR CODE HERE TO PRINT THE NAME(S) Of ANY PRESIDENT(s)
    //  WHO WERE BORN BEFORE THE STATES WERE FORMED = 10%

    Iterator<String> iterator = presidentsWithoutStates.iterator();
    while (iterator.hasNext()){
        System.out.println(iterator.next());
    }

我想知道如果我使用 ArrayList 而不是 …