我最近被问到如何为2D Array创建一个Java迭代器的问题,特别是如何实现:
public class PersonIterator implements Iterator<Person>{
private List<List<Person>> list;
public PersonIterator(List<List<Person>> list){
this.list = list;
}
@Override
public boolean hasNext() {
}
@Override
public Person next() {
}
}
通过使用索引来跟踪位置,1D 数组非常简单,有关如何为 2D 列表执行此操作的任何想法。
在 1D 情况下,您需要保留一个索引才能知道您离开的位置,对吗?好吧,在 2D 情况下,您需要两个索引:一个用于知道您正在哪个子列表中工作,另一个用于知道您离开该子列表中的哪个元素。
像这样的东西?(注:未经测试)
public class PersonIterator implements Iterator<Person>{
// This keeps track of the outer set of lists, the lists of lists
private Iterator<List<Person>> iterator;
// This tracks the inner set of lists, the lists of persons we're going through
private Iterator<Person> curIterator;
public PersonIterator(List<List<Person>> list){
// Set the outer one
this.iterator = list.iterator();
// And set the inner one based on whether or not we can
if (this.iterator.hasNext()) {
this.curIterator = iterator.next();
} else {
this.curIterator = null;
}
}
@Override
public boolean hasNext() {
// If the current iterator is valid then we obviously have another one
if (curIterator != null && curIterator.hasNext()) {
return true;
// Otherwise we need to safely get the iterator for the next list to iterate.
} else if (iterator.hasNext()) {
// We load a new iterator here
curIterator = iterator.next();
// and retry peeking to see if the new curIterator has any elements to iterate.
return hasNext();
// Otherwise we're out of lists.
} else {
return false;
}
}
@Override
public Person next() {
// Return the current value off the inner iterator if we can
if (curIterator != null && curIterator.hasNext()) {
return curIterator.next();
// Otherwise try to iterate along the next list and retry getting the next one.
// This won't infinitely loop at the end since next() at the end of the outer
// iterator should result in an NoSuchElementException.
} else {
curIterator = iterator.next();
return next();
}
}
}