[英]Custom iterator for linkedlist
我創建了一個自定義鏈表。 我也為此做了一個迭代器。 但據我所知,程序不會在方法size()中陷入循環。 它出什么問題了? 是關於我不正確的循環還是iterator()
。 每個節點都有字段: nextIndex
, prevIndex
, value
。
public class CustomLinkedList<E> implements List<E>{
private ListNode<E> header = new ListNode<>();
public CustomLinkedList() {
this.header = new ListNode();
}
@Override
public int size() {
int size = 0;
for(E it : this) {
size++;
}
return size;
}
@Override
public boolean isEmpty() {
if(this.header == null){
return true;
} else {return false;}
}
@Override
public boolean contains(Object o) {
if(((Integer) header.getValue() == 42) && ((Integer) header.getNextIndex().getValue() == 38)) return true;
return false;
}
@Override
public Iterator<E> iterator() {
return new Iterator<E>() {
private ListNode it = header;
@Override
public boolean hasNext() {
return (it.getNextIndex() != header) && (it.getNextIndex() != null);
}
@Override
public E next() {
it = it.getNextIndex();
return (E) it.getValue();
}
@Override
public void remove()
{
throw new UnsupportedOperationException("Iterator is read-only");
}
};
}
@Override
public boolean add(E e) {
ListNode<E> temp = new ListNode<>();
temp.setValue(e);
if (this.size() < 1) {
header.setValue(e);
header.setPrevIndex(header);
header.setNextIndex(header);
} else {
temp.setNextIndex(header);
ListNode tempLast = header.getPrevIndex();
tempLast.setNextIndex(temp);
header.setPrevIndex(temp);
temp.setPrevIndex(tempLast);
}
return true;
}
@Override
public boolean remove(Object o) {
return true;
}
@Override
public boolean containsAll(Collection<?> c) {
throw new NotImplementedException();
}
@Override
public void clear() {
throw new NotImplementedException();
}
@Override
public E get(int index) {
throw new NotImplementedException();
}
@Override
public int indexOf(Object o) {
throw new NotImplementedException();
}
@Override
public boolean addAll(Collection<? extends E> c) {
throw new NotImplementedException();
}
}
您從header.getNextIndex() == null
開始,然后調用一次add(E e)
。 在add()
內部, size()
將返回0,因此您可以設置header.setPrevIndex(header)
和header.setNextIndex(header)
接下來,再次調用add(E e)
. Inside
. Inside
的add() ,
大小() will call
hasNext() and
hasNext() will check (it.getNextIndex() != header) && (it.getNextIndex() != null)
將返回false,因為it.getNextIndex() == header
因此size()
始終小於1 。
並且您的代碼中還有許多其他錯誤。 更好的部分實現可能是這樣的
public class CustomLinkedList<E> implements List<E> {
private ListNode<E> header;
public CustomLinkedList() {
this.header = null;
}
@Override
public int size() {
int size = 0;
for (E it : this)
size++;
return size;
}
@Override
public boolean isEmpty() {
return header == null;
}
@Override
public boolean contains(Object obj) {
if (header != null)
for (E it : this)
if (it.equals(obj))
return true;
return false;
}
@Override
public Iterator<E> iterator() {
return new Iterator<E>() {
private ListNode<E> it = null;
@Override
public boolean hasNext() {
if (it==null && header!=null)
return true;
else if (it != null)
return it.getNextIndex() != null;
else
return false;
}
@Override
public E next() {
if (it==null)
it = header;
else
it = it.getNextIndex();
return it.getValue();
}
@Override
public void remove() {
throw new UnsupportedOperationException("Iterator is read-only");
}
};
}
@Override
public boolean add(E e) {
ListNode<E> temp = new ListNode<>();
temp.setValue(e);
if (header == null) {
header = temp;
} else {
ListNode<E> it = header;
while (it.getNextIndex() != null)
it = it.getNextIndex();
temp.setPrevIndex(it);
it.setNextIndex(temp);
}
return true;
}
}
您需要使用iterator
hasNext
和next
方法來iterator
元素並增加大小,例如:
@Override
public int size() {
int size = 0;
for(Iterator<String> it = this.iterator(); it.hasNext(); it.next()){
size++;
}
return size;
}
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