PriorityQueue has objects with the same priority

Question

I\'m using a priority queue to sort and use a large number of custom objects. The objects have a \"weight\" that is their natural ordering. However, different objects that a

Answer 1

If you need to have an ordering according the insertion order you need to use an extra element for timestamp. I.e. on insertions and equal weight use timestamp to see which element was inserted first. So CustomObject should be something like:

class CustomObject {  
   int weight;  
   long timestamp;  
}

And the comparison should be:

public int compareTo (CustomObject o) {  
    int thisWeight = this.weight;  
    int thatWeight = o.weight;  
    if (thisWeight != thatWeight) {  
        return thisWeight - thatWeight;  
    }  
    else {  
        return this.timestamp - o.timestamp;  
    }  
}  

The smaller timestamp means it was inserted earlier so you keep in the insertion order.

You could also use a "logical" time by maintaining a counter that you update on each add or remove.