Java で独自のリスト システムを実装しようとしています。
クラスListファイル:
package RoutingDemo.List;
/**
* A 2-way Linked-List to store generic elements.
*
*/
public class List {
/*
Instance Variables
---------------------------------------------------------------------------
*/
/**
* Reference to element.
*/
private Object info;
/**
* Reference to previous NodeList instance.
*/
private List prev;
/**
* Reference to next NodeList instance.
*/
private List next;
/*
Constructors
---------------------------------------------------------------------------
*/
/**
* Creates a new empty list.
*/
public List() {
prev = null;
next = null;
info = null;
}
/*
Methods
---------------------------------------------------------------------------
*/
/**
* Adds an element to the list.
*
* @param o Element to be added
*/
public List add(Object o) {
if(info == null) {
info = o;
prev = null;
next = null;
return this;
} else {
List temp = new List();
temp.add(o);
return addList(temp);
}
}
/**
* Appends an existing list to this list.
*
* @param newList List to be appended
*/
public List addList(List newList) {
if(newList.info() == null)
return this;
List ref = this;
ref.last().setNext(newList.first());
newList.first().setPrev(ref.last());
return ref;
}
/**
* Get number of elements in the list.
*
* @return number of elements in list
*/
public int count() {
if(info == null)
return 0;
List ref = this.first();
int count = 0;
while(true) {
count++;
if(!ref.isLast())
ref = ref.next();
else
break;
}
return count;
}
/**
* Deletes an element from the list.
*
* @param o Element to be deleted
* @return List which does NOT
* contain element o
*/
public List delete(Object o) {
if(info == null)
return this;
List ref = this.first();
while(true) {
if(ref.info() == o) {
if(ref.isFirst() && ref.isLast()) {
ref = new List();
break;
} else if(ref.isFirst()) {
ref = ref.next();
ref.killPrev();
break;
} else if(ref.isLast()) {
/* *** THIS IS THE CASE THAT WILL BE CALLED FOR THIS TEST **** */
ref = ref.prev();
ref.killNext();
break;
} else {
ref.prev().setNext(ref.next());
ref.next().setPrev(ref.prev());
ref = ref.prev();
break;
}
} else {
if(!ref.isLast())
ref = ref.next();
else
break;
}
}
return ref;
}
/**
* Moves to first element in List.
*
*
* @return List pointing to first
* element in list
*/
public List first() {
List ref = this;
while(!ref.isFirst()) {
/* *** STUCK HERE *** */
ref = ref.prev();
}
return ref;
}
/**
* Returns current list element.
*
* @return current list element
*/
public Object info() {
return info;
}
/**
* Checks whether list is empty.
*
* @return true, if list is empty
* , false otherwise.
*/
public boolean isEmpty() {
if(count() > 0)
return false;
else
return true;
}
/**
* Checks whether current element is the first element.
*
* @return true, if current element is
* first element, false otherwise.
*/
public boolean isFirst() {
if(prev == null)
return true;
else
return false;
}
/**
* checks whether current element is the last element.
*
* @return true, if current element is
* last element, false otherwise
*/
public boolean isLast() {
if(next == null)
return true;
else
return false;
}
/**
* Cuts the list from next element.
*
*
* @param l new link for current element
*/
public void killNext() {
next = null;
}
/**
* Cuts the list from previous element.
*
*
* @param l new link
*/
public void killPrev() {
prev = null;
}
/**
* Moves to last element in List.
*
*
* @return List pointing to last
* element in list
*/
public List last() {
List ref = this;
while(!ref.isLast()) {
ref = ref.next();
}
return ref;
}
/**
* Moves to next element in List
*
*
* @return List pointing to next
* element in list
*/
public List next() {
if(!isLast())
return next;
else
return this;
}
/**
* Moves to previous element in List
*
*
* @return List pointing to previous
* element in list
*/
public List prev() {
if(!isFirst())
return prev;
else
return this;
}
/**
* Sets the next link
*
*
* @param l new link for current element
*/
public void setNext(List l) {
next = l;
}
/**
* Sets the prev link for current element
*
*
* @param l new link
*/
public void setPrev(List l) {
prev = l;
}
}
そして、私はそれを次のようにテストしていました：
class Example {
Example() {
List nl = new List();
nl = nl.add(new Node(5,6));
System.out.println("" + nl.count());
Node x = new Node(1,3);
nl = nl.add(x);
System.out.println("" + nl.count());
nl = nl.delete(x);
System.out.println("as" + nl.count());
}
}
public class ListTest {
public static void main(String args[]) {
new Example();
}
}
最初の 2 つのノードを追加すると、すべて問題ありません。ただし、ノードを削除したcount() 後にを呼び出すと、無限ループに陥ります。
そして、多くのブレークポイントを通過した後、コード内でスタックしている場所をマークしました。どうやらdelete()関数に何か問題があるようです。何が間違っているのかわかりません。
とりあえず、delete()コードを次のように置き換えました。
public List delete(Object o) {
if(info == null)
return this;
List ref = this.first();
List temp = new List();
while(true) {
if(ref.info() != o)
temp.add(ref.info());
if(!ref.isLast())
ref = ref.next();
else
break;
}
return temp;
}
しかし、これは巨大なリストのメモリに優しくありません。問題を見つけることができたら教えてください！