Add Key and Value into an Priority Queue and Sort by Key in Java

Question

I am trying to take in a List of strings and add them into a Priority Queue with Key and Value. The Key being the word and the value being the string value of the word. Then I need to sort the queue with the highest string value first. The priority queue is not letting me add 2 values.

public static List<String> pQSortStrings(List<String> strings) {
    PriorityQueue<String, Integer> q = new PriorityQueue<>();

    for (int x = 0; x < strings.size(); x++) {
        q.add(strings.get(x),calculateStringValue(strings.get(x)));
    }
    return strings;
}

Answer 1

Problem

PriorityQueue can store a single object in it's each node. So what you are trying to do can not be done as it is.

But you can compose both objects in a single class and then use the PriorityQueue.

You would either need to supply a Comparator or rely on natural ordering by implementing Comparable interface.

---

Solution

• Create a class which has String and int as it's members.

  public class Entry {
      private String key;
      private int value;
  
      // Constructors, getters etc.
  }
  

• Implement Comparable interface and delegate comparison to String.

  public class Entry implements Comparable<Entry> {
      private String key;
      private int value;
  
      public Entry(String key, int value) {
          this.key = key;
          this.value = value;
      }
  
      // getters
  
      @Override
      public int compareTo(Entry other) {
          return this.getKey().compareTo(other.getKey());
      }
  }
  

• Build the PriorityQueue using this class.

  PriorityQueue<Entry> q = new PriorityQueue<>();
  

• Add elements as following.

  q.add(new Entry(strings.get(x), calculateStringValue(strings.get(x))));
  

Hope this helps.