Three things which seem questionable to me (I don't do much Java so I'm not entirely familiar with all the language features):

1. You access the private final priorityQueue which is the backing data structure directly within Song (songsQueue.priorityQueue.poll())

2. The only public read access to your queue is a method labelled "Do not use"

3. You have a method in your queue as part of your public interface which is commented as "Do not use". Either remove it, or simply state the draw backs so the user can make it's own decision.

Three things which seem questionable to me (I don't do much Java so I'm not entirely familiar with all the language features):

1. You access the private final priorityQueue which is the backing data structure directly within Song (songsQueue.priorityQueue.poll())

2. The only public read access to your queue is a method labelled "Do not use"

3. You have a method in your queue as part of your public interface which is commented as "Do not use". Either remove it, or simply state the draw backs so the user can make it's own decision.

Update

One more thing:

solveUsingFixedPriorityQueue() contains too much responsibility: it reads the data, solves the problem and outputs the data. Those concerns should be separated:

• Have one method reading the input and building the list of songs
• Pass the list of song to the solve method which should return the resulting list/array
• Have another write method generating the output by being passed in a list of songs.