java TreeSet问题

代码：
public class A {
public static void main(String[] args) {
SortedSet st = new TreeSet(Arrays.asList("one two tree four five six seven eight".split(" ")));
Object low = st.first(),
high = st.last();
Iterator it = st.iterator();
for(int i = 0;i < 6;i++){
if(i ==3)
low = it.next();
if(i == 6)
high = it.next();
else it.next();
}
System.out.println(low);
System.out.println(high);
}
}
为什么结果是：one two而不是one tree

public class A {
    public static void main(String[] args) {
        SortedSet<String> st = new TreeSet<String>(Arrays.asList("one two tree four five six seven eight".split(" ")));
        Object low = st.first(),
                high = st.last();
        System.out.println(st);
        Iterator<String> it = st.iterator();
        for(int i = 0;i < st.size();i++){
            if(i ==3)
                low = it.next();
            else if(i == 6)
                high = it.next();
            else it.next();
        }
        System.out.println(low);
        System.out.println(high);
    }
}

因为在 if(i ==3) low = it.next(); 时，你让it.next();又前进了一步~但是你的i却没有立刻++