Priority Queue add help?
ok, I'm making a priority queue from a List and I'm trying to figure out how to add to the queue so that the items are stored in the queue in order and this is what I have.
On the line that starts if(newItem.compareTo... eclipse is giving me a warning:
Type safety: The method compareTo(Object) belongs to the raw type Comparable. References to generic type Comparable<T> should be parameterized
And I dont know what that means? will my add method work as planned?
Also, my List class has a max size (that is private) and I want it so that if the priority queue tries to add over the max size it will throw an exception but the commented out line just causes an error...any ideas?
Thanks
public void enqueue(Comparable newItem) throws QueueException
//if(aList.size() == MAXLIST) throws Exception
if(aList.size() == 0) aList.add(1, newItem);
else
for(int i = 1; i <= aList.size(); i++)
if(newItem.compareTo(aList.get(i)) == -1) aList.add(i, newItem);
}
And I dont know what that means? The warning is referring to generics: http://java.sun.com/docs/books/tutorial/extra/generics/index.html
Similar Messages
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Priority Queue add (eclipse sign) help?
made this topic by accident...can anyone delete?
Message was edited by:
Jongono, but don't worry about it, you've acknowledged your own cross-post
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Does the priority queue always work?
Hi
I have a 8Mbp of wan link which sometime gets saturated and I have shaped average this to 8Mbps but i am running vocie on this WAN link and have defined priority for voice with 850kbps under voice class. My question is when the link is not fully utilized, Will the packets from priority queue are always dequeued first as compared to packets sent from from other queus or will the QoS will not do anything here since the link utilization is lot less than what is sepecified in shape average. I am asking this to confirm if the priority queue always help to overcome the issue of jitter if either the link is saturated or not?
ThanksDisclaimer
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You describe PQ and shaping, but the former is usually a part of doing QoS on L2/L3 switches, and the latter on routers. What device(s) and their IOS versions and the WAN media are you working with?
On "routers", interfaces generally have FIFO tx-rings, only when they overflow, are packets placed in CBWFQ queues. Within CBWFQ, LLQ will be dequeued first, but such packets might have already been queued behind other non-LLQ traffic within the interface tx-ring. (NB: for routers, with tx-rings, when supporting VoIP, you may want to minimize the size of the tx-ring.)
Shapers, in my experience, are "interesting". First, I believe many shapers don't account for L2 overhead, but provider CIRs often do. So unless you shape slower than the nomimal CIR rate, you can send faster than the available bandwidth. (Often I've found shaping 10 to 15% slower allows for average L2 overhead.)
Second, shapers work on averages over time intervals. For VoIP, you'll often want to insure the shaper is using a small Tc, otherwise it will allow FIFO bursts. (I've found a Tc of 10ms seems to support VoIP fairly well.)
Third, I suspect some shapers might have their own queues between the interface and the defined policy queues. If they do, unknown what their queuing organization is or their supported queuing depths. If this is the case, makes it difficult to engineer QoS.
Whenever possible, I've found it beneficial to work to avoid using shapers especially for timing sensitive traffic, like VoIP. In your case, I would suggest, if possible, obtaining 10 Mbps of WAN bandwidth and somewhere passing the traffic through a physical 10 Mbps interface, with a QoS policy.
But to more directly answer your question, PQ (or LQ) will dequeue its packets next compared to other "peer" queues. This should always help VoIP for delay and jitter, but there's more involved whether this is necessary and/or whether it's helpful enough when necessary.
You ask about when a link is saturated, but a link is 100% saturated everytime a packet is being transmitted. Often link usage is represented in percentages of usage of possible maximum transmission rate over some time period, but when it comes to QoS, 100% utilization might be just fine while 1% utilization is not. Much, much more information, about your situation, might be needed to offer truly constructive recommendations. -
D-ary heap with Priority Queue implementation
I have to construct a program that find the k-th smallest integer in a given set S of numbers; read from the standard input a first line containing positive integers N, k, and d separated by spaces. Each of the following N lines contains a positive integer of the set S. I have to implement a generic d-ary heap class that implements all methods of the priority queue interface.
i have the following code...but the inserting bubbling doesnt seem to wokr right...
any help would be great:
import java.util.*;
public class Heap {
static Element[] heap;
int N;
static int k;
int d;
static int size = 0;
Compare comp;
public Heap(int nodes, int max, Compare c)
N = max;
d = nodes;
heap = new Element[N];
comp = c;
public static void main(String args[])
Scanner _scan = new Scanner(System.in);
// String Nkd = _scan.nextLine();
// Scanner _scanNkd = new Scanner(Nkd);
int _N = 0;
int _d = 0;
Compare _c = new Compare();
_N = _scan.nextInt();
k = _scan.nextInt();
_d = _scan.nextInt();
Heap _heap = new Heap(_d,_N,_c);
int i=0;
int num=0;
while(_scan.hasNextLine()&&num<_N)
System.out.println("test" + _scan.nextInt());
_heap.insert(i, _scan.nextInt());
i++;
size++;
num++;
for(int z=0;z<_N;z++)
// System.out.println(heap[z].getKey());
Element kth = null;
for(int j = 1; j <=k; j++)
kth = _heap.removeMin();
System.out.print(kth.getKey());
System.out.print('\n');
/*System.out.print(k);
System.out.print('\n');
System.out.print(_heap.size());
System.out.print('\n');
System.out.print('\n');
System.out.print(heap[0].getKey());
System.out.print('\n');
System.out.print(heap[1].getKey());
System.out.print('\n');
System.out.print(heap[2].getKey());
System.out.print('\n');
System.out.print(heap[3].getKey());
System.out.print('\n');
System.out.print(heap[4].getKey());
System.out.print('\n');
System.out.print(heap[5].getKey());*/
public void insert(int i, int e)
heap[i] = new Element(e,i);
this.bubbleUp(heap);
public int size() {return size;}
public boolean isEmpty() {return(size == 0);}
public int min(){return heap[0].getKey();}
public Element remove()
int i = size-1;
size--;
return heap[i];
public Element removeMin()
Element min = this.root();
if(size == 1)
this.remove();
else
this.replace(this.root(), this.remove());
this.bubbleDown(this.root());
return min;
public Element replace(Element a, Element b)
a.setIndex(b.getIndex());
a.setKey(b.getKey());
return a;
public void bubbleUp(Element e)
Element f;
while(!e.isRoot(e.getIndex()))
f = this.getParent(e.getIndex());
if(comp.compare(f,e) <= 0)
break;
else
int temp = f.getIndex();
f.setIndex(e.getIndex());
e.setIndex(temp);
swap(f,e);
System.out.println("bubbling");
e=f;
public void bubbleDown(Element e)
int i = e.getIndex();
while(e.isInternal(i, size))
Element s;
if(!e.hasRight(i, size))
s = this.getLeft(i);
else if(comp.compare(this.getLeft(i), this.getRight(i)) <= 0)
s = this.getLeft(i);
else
s = this.getRight(i);
if(comp.compare(s,e) < 0)
swap(e,s);
e = s;
else
break;
public void swap(Element x, Element y)
int temp = x.getIndex();
x.setIndex(y.getIndex());
y.setIndex(temp);
public Element root() {return heap[0];}
public Element getLeft(int i) {return heap[i*2];}
public Element getRight(int i) {return heap[i*2+1];}
public Element getParent(int i) {return heap[i/2];}
class Element
private int key;
private int index;
public Element(int k, int i)
key = k;
index = i;
public int getKey() {return key;}
public void setKey(int k) {key = k;}
public int getIndex() {return index;}
public void setIndex(int i) {index = i;}
public boolean isRoot(int i) {
if (i == 0)
return true;
else
return false;
//return i == 1;
public boolean hasLeft(int i, int size) {return 2*i <= size;}
public boolean hasRight(int i, int size) {return 2*i+1 <= size;}
public boolean isInternal(int i, int size) {return hasLeft(i, size);}
public boolean isExternal(int i, int size) {return !isInternal(i, size);}
class Compare implements Comparator<Element>
public Compare(){}
public int compare(Element a, Element b)
int x=0;
if(a.getKey() < b.getKey())
x = -1;
else if(a.getKey() == b.getKey())
x = 0;
else if(a.getKey() > b.getKey())
x = 1;
return x;Well, this might be a swifty thing to do, unfortunately the Java Dudes in their infinite wisdom decided that asynchronous servlets were a bad thing. I disagree mind you. So while you could do what you wanted, you still have all these threads hangin' out waiting for their work to be done, which is just really lamo.
Anyhoo, to do this, just add a reference to the socket in the entry class, and when you pick up an entry from the heap, you can fetch the socket again, and send the results back to that socket. Of course you're probably going to moof up session info, and timeouts et. cetera, but it might work. -
Hi all,
i have written a priority queue which implements a priority queue interface however i'm getting a liitle stuck. I'm pretty new to Java programming, i'm trying to write a hosptial simulation where ill people arrive and are given a priority to be seen by a medic.
Every patient that is added to the queue has an int prioriy and the patient that is serviced next is the one with the highest priority. There are three priorities, low, medium, high. If more than one patient has the same highest priority, the patient with that priority that has been longest in the queue will be serviced.
Could you please help me out to see where my mistakes are?
Thanks
The priority queue interface
import java.util.Iterator;
public interface PriorityQueue
* Adds element to the priority queue
* @param element - the element to be added to the queue.
public void add (Priority element);
* Removes the next element from the priority queue
* Precondition: size() != 0
public void remove ();
* The next element to be serviced. This is the element in the queue that has
* the highest priority. If more than one element has the highest priority,
* the one which was added to the queue earliest is returned.
* Note that this has no effect on the queue - you must call remove as well to
* change the queue state.
* Precondition: size() != 0
* @return the next element to be serviced.
public Priority next();
* @return the number of elements in the priority queue
public int size();
* @return an Iterator for the priority queue.
public Iterator iterator
The priority queue
import java.util.ArrayList;
import java.util.Iterator;
public class PriorityQueueImpl implements PriorityQueue
private final static int DEFAULT_PRIORITY_COUNT = 3;
private ArrayList elements = new ArrayList();
public void add (Priority element)
elements.add (element);
public void remove ()
Iterator it = elements.iterator();
it.remove();
public Priority next()
Iterator it = elements.iterator();
Priority p, highestPriority;
while (it.hasNext())
p = it.next();
if (p.priority > highestPriority.priority)
highestPriority = p;
else if (p.priority == highestPriority.priority &&
p.admissionTime < highestPriority.admissionTime)
highestPriority = p;
public Iterator iterator()
Iterator it = new Iterator()
int size = size();
int priority = priority;
return it;
public int size()
int size = 0;
if (queue[i] !=null)
size += queue.size();
return size;Hi there,
I guess you are on the Herts uni course like myself, right? Have you had any luck with getting this to work, or are you still stuck like me?!
cheers
Matt Brett -
I am trying to develop Priority Queue using vector. For inserting elements I need to check if the inserted objects have greater key I want to shift them. In short, I want to store objects in vector in sorted manner (sort by key). I need help for that.
The code I have created so far is like this:
import PriorityQueue;
import java.util.*;
import java.io.*;
public class PQItem
private Object e;
private int k;
public PQItem(int key, Object element)
k=key;
e=element;
public int key(){ return k;}
public Object elelment(){ return e;}
public void setkey(int key){k=key;}
public void setElement(Object element){e=element;}
public static void main(String args[])
FileReader fr;
fr = openfile();
public static FileReader openfile()
String line,name,file="test.txt";
int vsize,k1,i1=0;
boolean flag;
Object e1,e2;
//Vector v = new Vector();
PriorityQueue q=new PriorityQueue();
try
FileReader fr=new FileReader(file);
BufferedReader inFile = new BufferedReader(fr);
String del=",";
line=inFile.readLine();
StringTokenizer tokenizer=new StringTokenizer(line,del);
while(line!=null)
tokenizer = new StringTokenizer(line,del);
k1 = Integer.parseInt(tokenizer.nextToken());
e1 = tokenizer.nextToken();
//System.out.println(line);
q.InsertItem(line,i1);
line=inFile.readLine();
i1++;
flag=q.isEmpty();
System.out.println(flag);
vsize=q.size();
System.out.println(+vsize);
e2=q.last();
System.out.println(e2);
}//try
catch(FileNotFoundException exception)
System.out.println("The File "+file+" was not found");
catch(IOException exception)
System.out.println(exception);
return null;
}//filereader
//The other file is
import java.util.*;
public class PriorityQueue
private Object[] a;
Vector v = new Vector();
//Constructor
public PriorityQueue()
public int size() {return v.size();}
public boolean isEmpty() { return (v.size())==0;}
public void InsertItem(Object e,int k)
v.insertElementAt(e,k);
//new code
//for(int i=0;i<size;i++)
public Object last()
return v.lastElement();Why not let Java do the work - use a java.util.TreeSet instead of a Vector.
Make your PQItem implement Comparable, write a compareTo(Object o) method (and an equals method for completeness) and you're golden. Then when you add(pqItem) it goes in the exact spot it belongs. -
Custom order of priority queue
I am a novice in Java. I intend to use a priority queue which holds objects. The objects have a string and two integers. I have to order the priority queue based on one of the integer.
I write syntax according to my understanding please correct me.
PriorityQueue<Object> pr = new PriorityQueue<Object>();
comparable(){
sort(Object.int2)// this is the place where I am confused
}Here's an example:
public class Caller
public static void main(String[] args)
Flight f1 = new Flight( "java", 2, 34 );
Flight f2 = new Flight( "java", 2, 3 );
Flight f3 = new Flight( "java", 2, 4 );
Flight f4 = new Flight( "java", 2, 64 );
Flight f5 = new Flight( "java", 2, 22 );
Flight f6 = new Flight( "java", 2, 12 );
PriorityQueue pq = new PriorityQueue();
pq.add(f1);
pq.add(f2);
pq.add(f3);
pq.add(f4);
pq.add(f5);
pq.add(f6);
System.out.println(pq.poll());
System.out.println(pq.poll());
System.out.println(pq.poll());
System.out.println(pq.poll());
System.out.println(pq.poll());
System.out.println(pq.poll());
public class Flight implements Comparable
private String airlinename;
private int flightnumber;
private int number;
public int compareTo(Object o)
Flight f = (Flight) o;
return number - f.getNumber();
public String toString()
return airlinename + " - " + number;
public Flight(String airname, int num1, int num2)
airlinename = airname;
flightnumber = num1;
number = num2;
public String getAirlinename()
return airlinename;
public void setAirlinename(String airlinename)
this.airlinename = airlinename;
public int getFlightnumber()
return flightnumber;
public void setFlightnumber(int flightnumber)
this.flightnumber = flightnumber;
public int getNumber()
return number;
public void setNumber(int number)
this.number = number;
}Got it? -
hi iam a beginner in java, could you please help me with this code. thanks
Implement (provide complete Java code) a priority queue using a singly linked list. You may call this class LinkedPriorityQueue. The use of classes contained in the Java Collections framework in the above implementing is strictly forbidden.
You may need to write a second class, PQNode, which defines the nodes in your linked list. Feel free to implement the PQNode class in anyway that you see fit. However, the LinkedPriorityQueue class should implement all methods and constructorsHere is the search of the forums
http://search.java.sun.com/search/java/index.jsp?qp=&nh=10&qt=%22singly+linked+list%22&col=javaforums&x=23&y=16
Here is a google search
http://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=%22singly+linked+list%22+java
Due tomorrow??? -
Hi Everybody.
Can anyone tell me in which order elements of priority queue are sorted.
I have used following code
class Test{
PriorityQueue <strings> pq=new PriorityQueue <Strings>();
pq.add("silpa");
pq.add("swati");
pq.add("roopa");
pq.add("abc");
System.out.println(pq);
System.out.println(pq.poll());
System.out.println(pq.peak());
The output I got is
[abc silpa swathi roopa]
abc
roopa.
Can anybody explain why the collection elements are not sorted ?
I am getting correct output with peek() n poll().According that methods i should get
[abc roopa silpa swathi ]
Explain the reason?System.out.println(pq);This line prints out the contents of the queue, by implicitly calling pq.toString(), whose behaviour is inherited from AbstractCollection, which therefore has nothing to do with sorting. So you have no valid reason for expecting any particular ordering.
-
How Queues functionality helps in Service Module
Hi,
How Queues functionality helps in Service Module.
how to get the queue details assign to the service call(Technician)
Please Suggest
Regards
VikramSridharan,
How to add technician to a queue.
Employee should be user of SAP?
Please Suggest.
Vikram -
Egress queueing - priority-queues and queue-sets
If I use the priority-queue out command on an interface 3750 does this treat queue1 as the priority queue?
How can I tell which traffic is sent to each queue by default? Or do I have to specifically define it such as
mls qos srr-queue output dscp-map queue 1 threshold 3 40 41 42 43 44 45 46 47
I really want dscp 40-47 to go priority and the rest to be spread evenly across the other 3 queues as the vast majority of the rest of the traffic will be 0. Is there a command that lets the other 3 queues be best effort?
Also, is this an OK config to use with priority-queueing? I don't actually want a large amount of bandwidth for the priority traffic, just for it to be expidited.
Queueset: 2
Queue : 1 2 3 4
buffers : 10 30 30 30
threshold1: 100 200 100 100
threshold2: 100 200 100 100
reserved : 50 50 50 50
maximum : 400 400 400 400
Any help very gratefully received.
Thanks, JSorry, just bouncing this to see if anyone around today can help :)
-
Question: Priority Queue "deleteMin()" trouble
Hello, I am having trouble formulating a delete() method here, which could also be called deleteMin() here.
The priority queue, is suppose to have quick insertion O(1) time, and slow deletion O(N) because it's going to have to search through the unordered array, find the minimum object then delete it once "delete()" is called.
However, I am stuck on trying to come up with the logic for my delete() method....
Here's what I am thinking...
I need to examine all the items and shift half of them, on average, down to fill in the hole once the minimum item is found.
How would I find the minimum item, and once found how would I delete this? Any direction or statements you can show me to clear this up would be appreciated. Please see my code below :) Please excuse my empty javadocs as of right now, I do those last.
Thank you
* This class is to demonstrate.....
* @version 1.0
public class PriorityQ {
private int maxSize;
private long[] queArray;
private int nItems;
* Javadoc here
public PriorityQ(int s) // constructor
maxSize = s;
queArray = new long[maxSize];
nItems = 0;
* Javadoc here
public void insert(long value) {
queArray[nItems] = value;
nItems++;
* Javadoc here
public long remove () {
* Javadoc here
public long peekMin() {
return queArray[nItems - 1];
* Javadoc here
public boolean isEmpty() {
return (nItems == 0);
* Javadoc here
public boolean isFull() {
return (nItems == maxSize);
} // end class PriorityQ
class PriorityQApp {
public static void main(String[] args)
PriorityQ q1 = new PriorityQ(5);
q1.insert(30);
q1.insert(50);
q1.insert(10);
q1.insert(40);
while( !q1.isEmpty() )
long item = q1.remove();
System.out.print(item + " "); // 10, 20, 30, 40, 50
} // end while
System.out.println("");
} // end main()
} // end class PriorityQApp
// //////////////////////////////////////////////////////////////Edited by: Cole1988 on Feb 21, 2009 9:03 AMSorry no one got to you sooner.
Using your instance variables:
public long remove()
long minValue = Long.MAX_VALUE;
int minIndex = 0;
for(int i = 0; i < nItems; i++) //Here we iterate through all the items to find the smallest one
if(queArray[i] < minValue) //If this particular value is less than the smallest one found so far,
minValue = queArray; //This value is now the smallest one found so far
minIndex = i; //minIndex now contains the index of the smallest one found so far
/*Now we can remove the smallest term, because after the above iteration, minIndex is the index number of the smallest value and minValue is the smallest value.*/
for(int i = minIndex + 1; i < nItems; i++) //Starting at the term right AFTER the smallest one
queArray[i-1]=queArray[i]; //Copy the value into the space right BEFORE it
nItems--; //The number of items has decreased by one
return minValue;
}Note: This code does NOT resize your array after you remove an item; depending on how you'll implement it, you'll need to check if you're about to overflow the array by comparing nItems with queArray.length and resize your array accordingly.
It seems like you're a bit confused about loops and iterating through arrays; I'd recommend reviewing a good Java book or online tutorial and practicing with some basic array iterations before you go any farther. You've got the basic grasp of things, it just hasn't "clicked" for you yet. :)
Let me know if you need any more help or if you don't understand anything about what I just said.
Regards,
Alvin -
I tried to use priority queue which I saw on the JavaTM 2 Platform
Standard Ed. 5.0(on the web),but when I tried to create a priority queue for my work(PriorityQueue myQ = new PriorityQueue();)the compiler complaint about that,
"C:\Program Files\Xinox Software\JCreator LE\MyProjects\Trypq\Trypq.java:7: cannot resolve symbol"
and then I found that I can not find this priority queue class in JavaTM 2 Platform Std. Ed. v1.4.2,so what's wrong with this 2 different API,does it mean that I have to create the priority queue class by myself,because my work can only base on JavaTM 2 Platform Std. Ed. v1.4.2???
can you help?
thanks!The feature was added in the latest release of Java. If you want to use it, you have to have the latest release.
Some of the concurrency features added in 1.5 (J2SE 5.0) were taken from Doug Lea's util.concurrent library, but I don't believe this was one of them. For those that were you have the option of using Doug's excellent library with pre 1.5 code.
You could also write your own, but I wouldn't particularly recommend it if you can upgrade to J2SE 5.0
Dave. -
I'm working on a program where I am creating an adaptable priority queue with heaps and I implement the heaps with linked binary trees. Know of any good examples or links on the subject? I know fundamentally what do do, but the syntax is the issue. Thanks for any help.......
http://java.sun.com/j2se/1.5.0/docs/api/java/util/PriorityQueue.html
-
Here's A Question Using A Priority Queue and a DLL
Ifm trying to make a method that compares two objects that go into a DLL using a priority Queue. SO in other words lets say i have "5" go ino the DLL and then i have "2" that goes in i need to swap the 2 and the 5. And this goes on for any other objects inserted
private Comparable minPosition() throws EmptyPriorityQueueException {
if (size() == 0)
throw new EmptyPriorityQueueException ("No Elements In The Queue");
else
now this is what i got so far....but i know that i have toi make to vaiables and compare them? little help please?
ThanksUm, well im using the adapter class, List. so ive gone a bit further, but im not sure on what to do.....
private Comparable minPosition() throws EmptyPriorityQueueException {
if (size() == 0)
throw new EmptyPriorityQueueException ("No Elements In The Queue");
while (isEmpty()==false)
r = ((Comparable)elements.first());
s = ((Comparable)elements.next(elements));
then i can make r=s and make s serach for the next element,?
Can the experienced programmers help me out? Doesn't seem to be a tuff question.
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