I am using 2 LiveDatas from separate tables into the repository of my application. I add the two LiveDatas as sources to the CustomMediatorLiveData class which extends MediatorLiveData.
In the onChanged callback of addSource method for each LiveData, I send the values of both the LiveDatas into a method that combines both and returns a single LiveData which is set as the value for the CustomMediatorLiveData object. I am creating an object of this CustomMediatorLiveData in my Repository and passing the two LiveDatas as parameters for the constructor.
This runs and doesn't give any error but it is messing up the data within the LiveData itself.
example: If the date was originally 15th August 2020 then it can be something like 14th August 0001.
CustomMediatorLiveData:
public class CustomMediatorLiveData extends MediatorLiveData<List<Object>> {
private List<Note> notes = Collections.emptyList();
private List<RecurringTask> recurringTasks = Collections.emptyList();
public CustomMediatorLiveData(LiveData<List<Note>> liveNotes, LiveData<List<RecurringTask>> liveRecurringTasks) {
addSource(liveNotes, notes1 -> {
if (notes1 != null) {
this.notes = notes1;
}
setValue(combineData(notes,recurringTasks));
});
addSource(liveRecurringTasks, recurringTasks1 -> {
if (recurringTasks1 != null) {
this.recurringTasks = recurringTasks1;
}
setValue(combineData(notes,recurringTasks));
});
}
// This method adds the 2 lists into one and sorts them based on dates and priority.
private List<Object> combineData(List<Note> notes, List<RecurringTask> recurringTasks) {
List<Object> combinedList = new ArrayList<>();
if (notes != null && !notes.isEmpty())
combinedList.addAll(notes);
if(recurringTasks!=null && !recurringTasks.isEmpty())
combinedList.addAll(recurringTasks);
Collections.sort(combinedList, new Comparator<Object>() {
#Override
public int compare(Object o1, Object o2) {
Date d1, d2;
Note n1 = null, n2 = null;
RecurringTask r1 = null, r2 = null;
if (o1 instanceof Note && o2 instanceof Note) {
int hmm = Boolean.compare(((Note) o2).isPriority(), ((Note) o1).isPriority());
if (hmm != 0)
return hmm;
}
if (o1 instanceof Note) {
d1 = ((Note) o1).getEnd_date();
n1 = ((Note) o1);
} else {
d1 = ((RecurringTask) o1).getEnd_date();
r1 = ((RecurringTask) o1);
}
if (o2 instanceof Note) {
d2 = ((Note) o2).getEnd_date();
n2 = ((Note) o2);
} else {
d2 = ((RecurringTask) o2).getEnd_date();
r2 = ((RecurringTask) o2);
}
if (n1 != null) {
if (r2 != null) {
if (n1.isPriority()) {
return -1;
}
}
}
if (n2 != null) {
if (r1 != null) {
if (n2.isPriority()) {
return 1;
}
}
}
long l1 = d1.getTime() - d2.getTime();
if (l1 > 0) {
return 1;
} else if (l1 < 0) {
return -1;
} else {
return 0;
}
}
});
return combinedList;
}
}
Note Repository class:
public class NoteRepository {
private String DB_NAME = "db_task";
Context context;
private RecurringDao recurringDao;
private LiveData<List<RecurringTask>> upcomingRecurringTasks;
private LiveData<List<Note>> upcomingTasks;
private CustomMediatorLiveData customMediatorLiveData;
private NoteDatabase noteDatabase;
public NoteRepository(Context context) {
noteDatabase = NoteDatabase.getInstance(context);
recurringDao = noteDatabase.recurringDao();
upcomingRecurringTasks = recurringDao.getUpcomingRecurringTask();
upcomingTasks = noteDatabase.daoAccess().fetchUpcomingTasks();
this.context = context;
customMediatorLiveData = new CustomMediatorLiveData(upcomingTasks, upcomingRecurringTasks);
}
public LiveData<List<Object>> getCustomMediatorLiveData() {
return customMediatorLiveData;
}
public LiveData<List<RecurringTask>> getUpcomingRecurringTasks() {
return upcomingRecurringTasks;
}
public LiveData<List<Note>> fetchUpcomingTasks() {
return NoteDatabase.getInstance(context).daoAccess().fetchUpcomingTasks();
}
}
I have tried using the MediatorLiveData object and add the two LiveData sources to it in the repository itself and the same issue persists.
What is the correct way to implement this? How to combine 2 LiveDatas into a single LiveData that can be observed.
Related
I am trying to develop custom source for parallel GCS content scanning. The naive approach would be to loop through listObjects function calls:
while (...) {
Objects objects = gcsUtil.listObjects(bucket, prefix, pageToken);
pageToken = objects.getNextPageToken();
...
}
The problem is performance for the tens of millions objects.
Instead of the single thread code we can add delimiter / and submit parallel processed for each prefix found:
...
Objects objects = gcsUtil.listObjects(bucket, prefix, pageToken, "/");
for (String subPrefix : object.getPrefixes()) {
scanAsync(bucket, subPrefix);
}
...
Next idea was to try to wrap this logic in Splittable DoFn.
Choice of RestrictionTracker: I don't see how can be used any of exiting RestrictionTracker. So decided to write own. Restriction itself is basically list of prefixes to scan. tryClaim checks if there is more prefixes left and receive newly scanned to append them to current restriction. trySplit splits list of prefixes.
The problem that I faced that trySplit can be called before all subPrefixes are found. In this case current restriction may receive more work to do after it was splitted. And it seems that trySplit is being called until it returns a not null value for a given RestrictionTracker: after certain number of elements goes to the output or after 1 second via scheduler or when ProcessContext.resume() returned. This doesn't work in my case as new prefixes can be found at any time. And I can't checkpoint via return ProcessContext.resume() because if split was already done, possible work that left in current restriction will cause checkDone() function to fail.
Another problem that I suspect that I couldn't achieve parallel execution in DirectRunner. As trySplit was always called with fractionOfRemainder=0 and new RestrictionTracker was started only after current one completed its piece of work.
It would be also great to read more detailed explanation about Splittable DoFn components lifecycle. How parallel execution per element is achieved. And how and when state of RestrictionTracker can be modified.
UPD: Adding simplified code that should show intended implementation
#DoFn.BoundedPerElement
private static class ScannerDoFn extends DoFn<String, String> {
private transient GcsUtil gcsUtil;
#GetInitialRestriction
public ScannerRestriction getInitialRestriction(#Element String bucket) {
return ScannerRestriction.init(bucket);
}
#ProcessElement
public ProcessContinuation processElement(
ProcessContext c,
#Element String bucket,
RestrictionTracker<ScannerRestriction, ScannerPosition> tracker,
OutputReceiver<String> outputReceiver) {
if (gcsUtil == null) {
gcsUtil = c.getPipelineOptions().as(GcsOptions.class).getGcsUtil();
}
ScannerRestriction currentRestriction = tracker.currentRestriction();
ScannerPosition position = new ScannerPosition();
while (true) {
if (tracker.tryClaim(position)) {
if (position.completedCurrent) {
// position.clear();
// ideally I would to get checkpoint here before starting new work
return ProcessContinuation.resume();
}
try {
Objects objects = gcsUtil.listObjects(
currentRestriction.bucket,
position.currentPrefix,
position.currentPageToken,
"/");
if (objects.getItems() != null) {
for (StorageObject o : objects.getItems()) {
outputReceiver.output(o.getName());
}
}
if (objects.getPrefixes() != null) {
position.newPrefixes.addAll(objects.getPrefixes());
}
position.currentPageToken = objects.getNextPageToken();
if (position.currentPageToken == null) {
position.completedCurrent = true;
}
} catch (Throwable throwable) {
logger.error("Error during scan", throwable);
}
} else {
return ProcessContinuation.stop();
}
}
}
#NewTracker
public RestrictionTracker<ScannerRestriction, ScannerPosition> restrictionTracker(#Restriction ScannerRestriction restriction) {
return new ScannerRestrictionTracker(restriction);
}
#GetRestrictionCoder
public Coder<ScannerRestriction> getRestrictionCoder() {
return ScannerRestriction.getCoder();
}
}
public static class ScannerPosition {
private String currentPrefix;
private String currentPageToken;
private final List<String> newPrefixes;
private boolean completedCurrent;
public ScannerPosition() {
this.currentPrefix = null;
this.currentPageToken = null;
this.newPrefixes = Lists.newArrayList();
this.completedCurrent = false;
}
public void clear() {
this.currentPageToken = null;
this.currentPrefix = null;
this.completedCurrent = false;
}
}
private static class ScannerRestriction {
private final String bucket;
private final LinkedList<String> prefixes;
private ScannerRestriction(String bucket) {
this.bucket = bucket;
this.prefixes = Lists.newLinkedList();
}
public static ScannerRestriction init(String bucket) {
ScannerRestriction res = new ScannerRestriction(bucket);
res.prefixes.add("");
return res;
}
public ScannerRestriction empty() {
return new ScannerRestriction(bucket);
}
public boolean isEmpty() {
return prefixes.isEmpty();
}
public static Coder<ScannerRestriction> getCoder() {
return ScannerRestrictionCoder.INSTANCE;
}
private static class ScannerRestrictionCoder extends AtomicCoder<ScannerRestriction> {
private static final ScannerRestrictionCoder INSTANCE = new ScannerRestrictionCoder();
private final static Coder<List<String>> listCoder = ListCoder.of(StringUtf8Coder.of());
#Override
public void encode(ScannerRestriction value, OutputStream outStream) throws IOException {
NullableCoder.of(StringUtf8Coder.of()).encode(value.bucket, outStream);
listCoder.encode(value.prefixes, outStream);
}
#Override
public ScannerRestriction decode(InputStream inStream) throws IOException {
String bucket = NullableCoder.of(StringUtf8Coder.of()).decode(inStream);
List<String> prefixes = listCoder.decode(inStream);
ScannerRestriction res = new ScannerRestriction(bucket);
res.prefixes.addAll(prefixes);
return res;
}
}
}
private static class ScannerRestrictionTracker extends RestrictionTracker<ScannerRestriction, ScannerPosition> {
private ScannerRestriction restriction;
private ScannerPosition lastPosition = null;
ScannerRestrictionTracker(ScannerRestriction restriction) {
this.restriction = restriction;
}
#Override
public boolean tryClaim(ScannerPosition position) {
restriction.prefixes.addAll(position.newPrefixes);
position.newPrefixes.clear();
if (position.completedCurrent) {
// completed work for current prefix
assert lastPosition != null && lastPosition.currentPrefix.equals(position.currentPrefix);
lastPosition = null;
return true; // return true but we would need to claim again if we need to get next prefix
} else if (lastPosition != null && lastPosition.currentPrefix.equals(position.currentPrefix)) {
// proceed work for current prefix
lastPosition = position;
return true;
}
// looking for next prefix
assert position.currentPrefix == null;
assert lastPosition == null;
if (restriction.isEmpty()) {
// no work to do
return false;
}
position.currentPrefix = restriction.prefixes.poll();
lastPosition = position;
return true;
}
#Override
public ScannerRestriction currentRestriction() {
return restriction;
}
#Override
public SplitResult<ScannerRestriction> trySplit(double fractionOfRemainder) {
if (lastPosition == null && restriction.isEmpty()) {
// no work at all
return null;
}
if (lastPosition != null && restriction.isEmpty()) {
// work at the moment only at currently scanned prefix
return SplitResult.of(restriction, restriction.empty());
}
int size = restriction.prefixes.size();
int newSize = new Double(Math.round(fractionOfRemainder * size)).intValue();
if (newSize == 0) {
ScannerRestriction residual = restriction;
restriction = restriction.empty();
return SplitResult.of(restriction, residual);
}
ScannerRestriction residual = restriction.empty();
for (int i=newSize; i<=size; i++) {
residual.prefixes.add(restriction.prefixes.removeLast());
}
return SplitResult.of(restriction, residual);
}
#Override
public void checkDone() throws IllegalStateException {
if (lastPosition != null) {
throw new IllegalStateException("Called checkDone on not completed job");
}
}
#Override
public IsBounded isBounded() {
return IsBounded.UNBOUNDED;
}
}
I have the below code that is creating the PriortyQueue structure using Dart. But since I cannot use heapify function inside the Constructor or factory constructor I cannot initialize PQ with an existing set of List. Can somebody guide me and show me how I can use heapify while creating PQ instance so I can initialize it with an existing List? Also If you have any other suggestions against doing something like this please also help me as well. thank you
class PriorityQueue<T extends Comparable<T>> {
List<T?> _tree;
PriorityQueue._(List<T?> tree) : _tree = tree;
factory PriorityQueue([List<T>? array]) {
List<T?> newArray = [null, ...array ?? []];
// ignore: todo
//TODO: missing heapify
return PriorityQueue._(newArray);
}
void insert(T node) {
_tree.add(node);
_swim(_tree.length - 1);
}
T getTop() {
_swap(1, _tree.length - 1);
T top = _tree.removeLast() as T;
_sink(1);
return top;
}
List<T> _heapify(List<T> array) {
int sinkNodeIndex = (array.length - 1) ~/ 2;
while (sinkNodeIndex >= 1) {
_sink(sinkNodeIndex);
sinkNodeIndex--;
}
}
void _sink(int nodeIndex) {
int leftChildIndex = nodeIndex * 2;
int rightChildIndex = leftChildIndex + 1;
int minNodeIndex = leftChildIndex;
// index can be unreachable
T? leftChild =
leftChildIndex >= _tree.length ? null : _tree[leftChildIndex];
T? rightChild =
rightChildIndex >= _tree.length ? null : _tree[rightChildIndex];
if (leftChild == null) {
return;
}
if (rightChild != null && leftChild.compareTo(rightChild) > 0) {
minNodeIndex = rightChildIndex;
}
if ((_tree[minNodeIndex] as T).compareTo(_tree[nodeIndex] as T) < 0) {
_swap(nodeIndex, minNodeIndex);
_sink(minNodeIndex);
}
}
void _swim(int nodeIndex) {
if (nodeIndex <= 1) return;
int parentIndex = nodeIndex ~/ 2;
if ((_tree[nodeIndex] as T).compareTo(_tree[parentIndex] as T) < 0) {
_swap(nodeIndex, parentIndex);
_swim(parentIndex);
}
}
void _swap(int i, int j) {
T temp = _tree[i] as T;
_tree[i] = _tree[j];
_tree[j] = temp;
}
#override
String toString() {
return _tree.toString();
}
}
I would make all the helper functions. _heapify, _sink/_swim, even _swap, be static functions which take the list as argument.
Then you can use them from anywhere, including inside the factory constructor.
Alternatively, you can change the constructor to returning:
return PriorityQueue._(newArray).._heapify();
This creates the PriorityQueue object, and then calls the _heapify method on it, before returning the value.
(I'd also make _tree have type List<T> and not insert the extra null at the beginning. It's more efficient to add/subtract 1 from indices than it is to cast to T.)
I ended up doing like Irn's first suggestion. But when I do functions static they lost Type of the class so I needed to specify for each function. Also, making List<T?> instead of List ended up with me fighting against the compiler.
class PriorityQueue<T extends Comparable<T>> {
List<T?> _tree;
PriorityQueue._(List<T?> tree) : _tree = tree;
factory PriorityQueue([List<T>? array]) {
List<T?> newArray = [null, ...array ?? []];
_heapify(newArray);
return PriorityQueue._(newArray);
}
bool get isNotEmpty {
return _tree.isNotEmpty;
}
void insert(T node) {
_tree.add(node);
_swim(_tree, _tree.length - 1);
}
void insertMultiple(List<T> array) {
for (var element in array) {
insert(element);
}
}
T? removeTop() {
if (_tree.length == 1) return null;
_swap(_tree, 1, _tree.length - 1);
T top = _tree.removeLast() as T;
_sink(_tree, 1);
return top;
}
void removeAll() {
_tree = [null];
}
static void _heapify<T extends Comparable<T>>(List<T?> array) {
int sinkNodeIndex = (array.length - 1) ~/ 2;
while (sinkNodeIndex >= 1) {
_sink(array, sinkNodeIndex);
sinkNodeIndex--;
}
}
static void _sink<T extends Comparable<T>>(List<T?> tree, int nodeIndex) {
int leftChildIndex = nodeIndex * 2;
int rightChildIndex = leftChildIndex + 1;
int minNodeIndex = leftChildIndex;
T? leftChild = leftChildIndex >= tree.length ? null : tree[leftChildIndex];
T? rightChild =
rightChildIndex >= tree.length ? null : tree[rightChildIndex];
if (leftChild == null) {
return;
}
if (rightChild != null && leftChild.compareTo(rightChild) > 0) {
minNodeIndex = rightChildIndex;
}
if ((tree[minNodeIndex] as T).compareTo(tree[nodeIndex] as T) < 0) {
_swap(tree, nodeIndex, minNodeIndex);
_sink(tree, minNodeIndex);
}
}
static void _swim<T extends Comparable<T>>(List<T?> tree, int nodeIndex) {
if (nodeIndex <= 1) return;
int parentIndex = nodeIndex ~/ 2;
if ((tree[nodeIndex] as T).compareTo(tree[parentIndex] as T) < 0) {
_swap(tree, nodeIndex, parentIndex);
_swim(tree, parentIndex);
}
}
static void _swap<T extends Comparable<T>>(List<T?> tree, int i, int j) {
T temp = tree[i] as T;
tree[i] = tree[j];
tree[j] = temp;
}
#override
String toString() {
return _tree.toString();
}
}
I tried to use reverseBystack, reverseBylink and remove.. but I don't know why when i use these functions, it has error like this.
Exception in thread "main" java.lang.NullPointerException
at LinkedQueue$Node.access$200(LinkedQueue.java:44)
at LinkedQueue.reverseBylink(LinkedQueue.java:185)
at LinkedQueue.main(LinkedQueue.java:238)
void reverseByStack() - This method reverses the order of the items in the linked list (first
becomes last and last becomes first) using a stack data strucenter code hereture`
• void reverseByLinks() - This method also reverses the order of the items in the linked list.
It should not create a new list or use a stack. It should only reverse the order of the nodes by
modifying the next values for each node in the list.
• int remove(Item item) - This method scans the queue for occurrences of item and removes
them from the queue. It returns the number of items deleted from the queue.
these are what i want to make.
enter code here public class LinkedQueue<Item> implements Iterable<Item> {
private int N; // number of elements on queue
private Node first; // beginning of queue
private Node last; // end of queue
// helper linked list class
private class Node {
private Item item;
private Node next;
}
public LinkedQueue() {
first = null;
last = null;
N = 0;
assert check();
}
public boolean isEmpty() {
return first == null;
}
public int size() {
return N;
}
public Item peek() {
if (isEmpty()) throw new NoSuchElementException("Queue
underflow");
return first.item;
}
public void enqueue(Item item) {
Node oldlast = last;
last = new Node();
last.item = item;
last.next = null;
if (isEmpty()) first = last;
else oldlast.next = last;
N++;
assert check();
}
public Item dequeue() {
if (isEmpty()) throw new NoSuchElementException("Queue
underflow");
Item item = first.item;
first = first.next;
N--;
if (isEmpty()) last = null; // to avoid loitering
assert check();
return item;
}
public String toString() {
StringBuilder s = new StringBuilder();
for (Item item : this)
s.append(item + " ");
return s.toString();
}
private boolean check() {
if (N == 0) {
if (first != null) return false;
if (last != null) return false;
}
else if (N == 1) {
if (first == null || last == null) return false;
if (first != last) return false;
if (first.next != null) return false;
}
else {
if (first == last) return false;
if (first.next == null) return false;
if (last.next != null) return false;
// check internal consistency of instance variable N
int numberOfNodes = 0;
for (Node x = first; x != null; x = x.next) {
numberOfNodes++;
}
if (numberOfNodes != N) return false;
// check internal consistency of instance variable last
Node lastNode = first;
while (lastNode.next != null) {
lastNode = lastNode.next;
}
if (last != lastNode) return false;
}
return true;
}
void reverseBystack(){
Stack<Item> s = new Stack<>();
Item item;
while (s.isEmpty() != true){
item = dequeue();
s.push(item);
}
while(s.isEmpty() != true){
item = s.pop();
enqueue(item);
}
}
void reverseBylink() {
Node prev = null;
Node current = this.first;
Node next = null;
while (current != null) {
next = current.next;
current.next = prev;
prev = current;
current = next;
}
prev.next = current.next;
}
int remove(Item item){
Node cur = first;
Node prev = last;
while(cur != null) {
if(cur.item.equals(item))
System.out.println(cur.item);
}
cur = cur.next;
prev = cur.next;
return 0;
}
public Iterator<Item> iterator() {
return new ListIterator();
}
private class ListIterator implements Iterator<Item> {
private Node current = first;
public boolean hasNext() { return current != null;
}
public void remove() { throw new
UnsupportedOperationException(); }
public Item next() {
if (!hasNext()) throw new NoSuchElementException();
Item item = current.item;
current = current.next;
return item;
}
}
/**
* Unit tests the <tt>LinkedQueue</tt> data type.
*/
public static void main(String[] args) {
LinkedQueue<String> q = new LinkedQueue<String>();
while (!StdIn.isEmpty()) {
String item = StdIn.readString();
if (!item.equals("-")) q.reverseBylink();
else if (!q.isEmpty()) StdOut.print(q.dequeue() + " ");
}
StdOut.println("(" + q.size() + " left on queue)");
}
}
I am practicing build a doubly linked list contains string value.
In find method, I have a NullPointer Exception
here is my code.
package LinkedList;
package LinkedList;
public class LinkedList {
// 노드 클래스
class Node {
String value;
Node prev;
Node next;
Node(String v, Node p, Node s) {
value = v;
prev = p;
next = s;
}
public String getValue() {
return value;
}
public Node getPrev() {
return prev;
}
public Node getNext() {
return next;
}
public void setPrev(Node p) {
prev = p;
}
public void setNext(Node n) {
next = n;
}
}
Node head;
Node tail;
int size = 0;
public LinkedList() {
head = new Node(null, null, null);
tail = new Node(null, head, null);
head.setNext(tail);
}
public int size() {
return size;
}
public boolean isEmpty() {
return size == 0;
}
public String first() {
if (isEmpty()) {
return null;
}
return head.getNext().getValue();
}
public String last() {
if (isEmpty()) {
return null;
}
return tail.getPrev().getValue();
}
public void addFirst(String value) {
addBetween(value, head, head.getNext());
}
public void addLast(String value) {
addBetween(value, tail.getPrev(), tail);
}
public void addBetween(String v, Node p, Node s) {
Node newNode = new Node(v, p, s);
p.setNext(newNode);
s.setPrev(newNode);
size++;
}
public String remove(Node node) {
Node p = node.getPrev();
Node s = node.getNext();
p.setNext(s);
s.setPrev(p);
size--;
return node.getValue();
}
public String removeFirst() {
if (isEmpty()) {
return null;
}
return remove(head.getNext());
}
public String removeLast() {
if (isEmpty()) {
return null;
}
return remove(tail.getPrev());
}
public void insert(String value) {
Node current = head;
// first
if (isEmpty()) {
addFirst(value);
} else {
// check
while (current.getNext() != tail || current.getValue().compareTo(value) > 0) {
current = current.getNext();
}
// last
if (current.getNext() == tail) {
addLast(value);
} else // between
{
addBetween(value, current.getNext(), current);
}
}
}
/* !!!!!!!!!!!!!! ERORR !!!!!!!!!!!! */
public void find(String value) {
Node current = head.getNext();
while ((current != null) || !(current.getValue().equals(value)))
current = current.getNext();
if (current.getValue().equals(value)) {
System.out.println("found " + value);
} else {
System.out.println("Not found " + value);
}
}
// • Traverse the list forwards and print
// 순회
public void fowardTraverse() {
Node current = head.getNext();
System.out.print(current.getValue());
while (current.getNext() != tail) {
current = current.getNext();
System.out.print(" -> " + current.getValue());
}
}
// • Traverse the list backwards and print
// 뒤로 순회
public void backwardTraverse() {
Node current = tail.getPrev();
System.out.print(current.getValue());
while (current.getPrev() != head) {
current = current.getPrev();
System.out.print(" -> " + current.getValue());
}
}
// • Delete a node from the list
// 지우기
public String delete(String value) {
return value;
}
// • Delete/destroy the list
// 파괴하기
public void destroy() {
}
public static void main(String[] args) {
// TODO Auto-generated method stubs
LinkedList a = new LinkedList();
a.insert("a");
a.insert("b");
a.insert("c");
a.insert("d");
a.insert("e");
a.insert("f");
a.insert("g");
a.insert("h");
a.insert("i");
// a.fowardTraverse();
a.find("a");
}
I don't understand why I get a nullpointException at the line,
It suppose to put a node contains a.
Make sure you check for Non-NULL before dereferencing:
Node current = head.getNext();
and
if (current.getValue().equals(value)) {
to be replaced by
Node current;
if(head != NULL) current = head.getNext();
and
if (current != NULL && current.getValue().equals(value)) {
Because your Head is empty...(No pun intended)
before Addfirst calling..your structure:
head=[null,null,tail],tail=[null,head,null];
you are sending ("a",head,tail)
and your storing it in new node making it a structure like:
head=[null,null,newNode]==>newNode["a",head,tail]==>tail[null,newNode,null]
So search will compare null to a (in find) giving you the error .....
---Edit 1:
#JanghyupLee, My Bad, Didn't do a closer look on find method...however , I found that in condition of "if" you are using condition
current != null || ......
After first line that is ( current=head.next)..current becomes not null..
which is causing the condition in while to ignore the right part of '||' (short circuit) until current has a value of null...
Once the current becomes null then it goes for the next statement to check for value..causing null pointer exception
I am evaluating the performance of Microsoft's implementation of Avro, and at first I thought I was getting phenomenal performance until I realized it just wasn't serializing the entire message ;-)
In the following there is a simple hierarchy of messages decorated with [DataContract] (a base and two derived types). All members are decorated with the [DataMember] attribute. I create a serializer from the base message type and serialize a list of derived messages, but it appears to only serialize/deserialize the base class members. All of the derived message members are missing from the result.
Am I missing something? My application will require mixed message types.
FWIW I don't see any strings from the second derived type in the binary file, so I suspect the derived type members aren't being serialized.
Thanks, Greg
class Program
{
[DataContract(Name = "SideType", Namespace = "AvroMessage")]
public enum EventType
{
Unknown = 0,
One = 1,
Two = 2
}
[DataContract(Name = "MessageBase", Namespace = "AvroMessage")]
public class MessageBase
{
[DataMember(Name = "Subtype")]
public string Subtype;
[DataMember(Name = "Timestamp")]
public DateTime Timestamp;
[DataMember(Name = "GroupName")]
public string GroupName;
public override bool Equals(object obj)
{
MessageBase other = obj as MessageBase;
if (other == null) return false;
return Subtype == other.Subtype &&
Timestamp == other.Timestamp &&
GroupName == other.GroupName;
}
}
[DataContract(Name = "SubMessage1", Namespace = "AvroMessage")]
public class SubMessage1 : MessageBase
{
[DataMember(Name = "Volume")]
public int Volume;
[DataMember(Name = "Count")]
public int Count;
[DataMember(Name = "DetectedSide")]
public EventType Event;
public override bool Equals(object obj)
{
SubMessage1 other = obj as SubMessage1;
if (other == null) return false;
return Subtype == other.Subtype &&
Timestamp == other.Timestamp &&
GroupName == other.GroupName &&
Event == other.Event &&
Volume == other.Volume &&
Count == other.Count;
}
}
[DataContract(Name = "SubMessage2", Namespace = "AvroMessage")]
public class SubMessage2 : MessageBase
{
[DataMember(Name = "Name1")]
public string Name1;
[DataMember(Name = "Volume1")]
public int Volume1;
[DataMember(Name = "Name2")]
public string Name2;
[DataMember(Name = "Volume2")]
public int Volume2;
[DataMember(Name = "PriceMove")]
public double PriceMove;
public override bool Equals(object obj)
{
SubMessage2 other = obj as SubMessage2;
if (other == null) return false;
return Subtype == other.Subtype &&
Timestamp == other.Timestamp &&
GroupName == other.GroupName &&
Volume1 == other.Volume1 &&
Name1 == other.Name1 &&
Volume2 == other.Volume2 &&
Name2 == other.Name2 &&
PriceMove == other.PriceMove;
}
}
public class MessageFactory
{
public static IEnumerable<MessageBase> CreateMessages(int number)
{
Random ran = new Random();
List<MessageBase> retval = new List<MessageBase>();
for (int i = 0; i < number; i++)
{
if (ran.Next(2) == 0)
{
SubMessage1 sub1 = new SubMessage1();
sub1.Timestamp = DateTime.Now;
sub1.GroupName = "Group" + DateTime.Now.Millisecond.ToString();
sub1.Subtype = "SubMessag1";
sub1.Volume = ran.Next(10000);
sub1.Count = ran.Next(100);
if (ran.Next(2) == 0)
{
sub1.Event = EventType.One;
}
else
{
sub1.Event = EventType.Two;
}
retval.Add(sub1);
}
else
{
SubMessage2 sub2 = new SubMessage2();
sub2.Timestamp = DateTime.Now;
sub2.GroupName = "Group" + DateTime.Now.Millisecond.ToString();
sub2.Subtype = "SubMessag2";
sub2.Volume1 = ran.Next(1000);
sub2.PriceMove = ran.NextDouble() * 100 - 50;
sub2.Volume2 = ran.Next(1000);
sub2.Name1 = "Contract" + (DateTime.Now.Millisecond + ran.Next(5)).ToString();
sub2.Name2 = "Contract" + DateTime.Now.Millisecond.ToString();
retval.Add(sub2);
}
}
return retval;
}
}
public static void TestAvro(int count)
{
bool correct = false;
long serTicks = 0;
long deserTicks = 0;
Stopwatch sw = new Stopwatch();
sw.Reset();
var serializer = Microsoft.Hadoop.Avro.AvroSerializer.Create<MessageBase>();
MessageBase[] messages = new MessageBase[count];
using (var file = File.Create(#"C:\test_avro.bin"))
{
int i = 0;
foreach (var message in MessageFactory.CreateMessages(count))
{
messages[i++] = message;
sw.Start();
serializer.Serialize(file, message);
sw.Stop();
}
}
serTicks = sw.ElapsedTicks;
sw.Reset();
List<int> badMessages = new List<int>();
using (var file = File.OpenRead(#"C:\test_avro.bin"))
{
for (int i = 0; i < count; i++)
{
sw.Start();
MessageBase message = serializer.Deserialize(file);
sw.Stop();
SubMessage1 m1 = message as SubMessage1;
SubMessage2 m2 = message as SubMessage2;
bool areNull = (m1 == null) && (m2 == null); // Always true
if (!messages[i].Equals(message)) badMessages.Add(i);
}
}
deserTicks = sw.ElapsedTicks;
correct = badMessages.Count == 0;
long size = (new FileInfo(#"C:\test_proto.bin")).Length;
Console.WriteLine(String.Format("Correct: {0}, Time Out: {1}, , Time In: {2}, , Size: {3}", correct, serTicks, deserTicks, size));
}
static void Main(string[] args)
{
TestAvro(10000);
Console.ReadLine();
}
}
My bad - I forgot the KnownType attribute on the base class, one for each derived type. It works if you include the attributes.