Why does this priority queue implementation only print one value repeatedly? - stack

Question

This program should print out the values in order ascending order. But it only displays 957.0 repeatedly. How do I display the numbers in order?
import java.io.*;
import java.util.*;
class PriorityQ {
public int maxSize;
public double[] queArray;
public int nItems;
//------
public PriorityQ(int s){
maxSize = s;
queArray = new double[maxSize];
nItems = 0;
}
//-----
public void insert(double item){
int j;
if(nItems == 0){
queArray[nItems++] = item;
}
else{
for(j = nItems-1; j >= 0; j--){
if(item > queArray[j]){
queArray[j + 1] = item;
}
else{
break;
}
}
queArray[j + 1] = item;
nItems++;
}
}
//-----
public double remove(){
return queArray[--nItems];
}
//-----
public double peekMin(){
return queArray[nItems - 1];
}
//-----
public boolean isEmpty(){
return(nItems == 0);
}
//-----
public boolean isFull(){
return(nItems == maxSize);
}
}
//-----
public class PriorityQApp{
public static void main(String[] args) throws IOException{
PriorityQ thePQ = new PriorityQ(5);
thePQ.insert(546);
thePQ.insert(687);
thePQ.insert(36);
thePQ.insert(98);
thePQ.insert(957);
while(!thePQ.isEmpty()){
double item = thePQ.remove();
System.out.print(item + " ");
}
System.out.println("");
}
}

Answer 1

You should save yourself the effort and use a priority queue with the generic type Double. If you wanted descending order you could even use a comparator that orders the highest value before the lowest, but you asked for ascending.
Your problem is that your array does contain many copies of 957.
This is because of this line in your code:
if(item > queArray[j]){
queArray[j + 1] = item;
}
Try:
import java.io.*;
import java.util.*;
public class PriorityQApp{
public static void main(String[] args) throws IOException{
PriorityQueue<Double> thePQ = new PriorityQueue<Double>(5);
thePQ.add(546);
thePQ.add(687);
thePQ.add(36);
thePQ.add(98);
thePQ.add(957);
while(thePQ.size() > 0){
double item = thePQ.poll();
System.out.print(item + " ");
}
System.out.println("");
}
}
Or I can fix your code to print out the queue in descending order leaving it to you to then make it print out in ascending order, the block I pointed to before should read like this instead:
if(item < queArray[j]){
queArray[j + 1] = queArray[j];
}