PriorityQueueExampleTest.java

package com.examplehub.basics.queue;

import static org.junit.jupiter.api.Assertions.*;

import java.util.Comparator;
import java.util.NoSuchElementException;
import java.util.PriorityQueue;
import org.junit.jupiter.api.Test;

class PriorityQueueExampleTest {
  @Test
  void testAdd() {
    PriorityQueue<String> queue = new PriorityQueue<>();
    queue.add("A");
    queue.add("C");
    queue.add("B");
    assertEquals("[A, C, B]", queue.toString());
  }

  @Test
  void testOffer() {
    PriorityQueue<String> queue = new PriorityQueue<>();
    assertTrue(queue.offer("A"));
    assertTrue(queue.offer("B"));
    assertTrue(queue.offer("C"));
    assertEquals("[A, B, C]", queue.toString());
  }

  @Test
  void testSize() {
    PriorityQueue<String> queue = new PriorityQueue<>();
    assertTrue(queue.offer("A"));
    assertEquals(1, queue.size());
  }

  @Test
  void testRemove() {
    PriorityQueue<String> queue = new PriorityQueue<>();
    assertTrue(queue.offer("B"));
    assertTrue(queue.offer("D"));
    assertTrue(queue.offer("C"));
    assertTrue(queue.offer("A"));

    assertEquals("A", queue.remove());
    assertEquals("B", queue.remove());
    assertEquals("C", queue.remove());
    assertEquals("D", queue.remove());

    assertEquals(0, queue.size());
    try {
      queue.remove();
      fail();
    } catch (NoSuchElementException e) {
      assertTrue(true);
    }
  }

  @Test
  void testPoll() {
    PriorityQueue<String> queue = new PriorityQueue<>();
    assertTrue(queue.offer("B"));
    assertTrue(queue.offer("D"));
    assertTrue(queue.offer("C"));
    assertTrue(queue.offer("A"));

    assertEquals("A", queue.poll());
    assertEquals("B", queue.poll());
    assertEquals("C", queue.poll());
    assertEquals("D", queue.poll());

    assertEquals(0, queue.size());

    assertNull(queue.poll());
  }

  @Test
  void testPeek() {
    PriorityQueue<String> queue = new PriorityQueue<>();
    assertTrue(queue.offer("B"));
    assertTrue(queue.offer("C"));
    assertTrue(queue.offer("A"));
    assertTrue(queue.offer("D"));

    assertEquals("A", queue.peek());
    assertEquals("A", queue.peek());
  }

  @Test
  void testElement() {
    PriorityQueue<String> queue = new PriorityQueue<>();
    assertTrue(queue.offer("B"));
    assertTrue(queue.offer("C"));
    assertTrue(queue.offer("A"));
    assertTrue(queue.offer("D"));

    assertEquals("A", queue.element());
    assertEquals("A", queue.element());
  }

  @Test
  void testComparable() {
    class User implements Comparable<User> {
      private String username;

      public User(String username) {
        this.username = username;
      }

      public String getUsername() {
        return username;
      }

      public void setUsername(String username) {
        this.username = username;
      }

      @Override
      public String toString() {
        return username;
      }

      @Override
      public int compareTo(User o) {
        return this.getUsername().compareTo(o.getUsername());
      }
    }

    PriorityQueue<User> priorityQueue = new PriorityQueue<>();
    priorityQueue.add(new User("google"));
    priorityQueue.add(new User("apple"));
    priorityQueue.add(new User("alibaba"));
    priorityQueue.add(new User("microsoft"));
    priorityQueue.add(new User("zoom"));

    assertNotNull(priorityQueue.peek());
    assertEquals("alibaba", priorityQueue.poll().getUsername());

    assertNotNull(priorityQueue.peek());
    assertEquals("apple", priorityQueue.peek().getUsername());

    assertNotNull(priorityQueue.peek());
    assertEquals("apple", priorityQueue.poll().getUsername());

    assertEquals("[google, microsoft, zoom]", priorityQueue.toString());
  }

  @Test
  void testComparator() {
    class User {
      private String username;

      public User(String username) {
        this.username = username;
      }

      public String getUsername() {
        return username;
      }

      public void setUsername(String username) {
        this.username = username;
      }

      @Override
      public String toString() {
        return username;
      }
    }

    PriorityQueue<User> priorityQueue =
        new PriorityQueue<>(
            new Comparator<User>() {
              @Override
              public int compare(User o1, User o2) {
                return o1.getUsername().compareTo(o2.getUsername());
              }
            });
    priorityQueue.add(new User("google"));
    priorityQueue.add(new User("apple"));
    priorityQueue.add(new User("alibaba"));
    priorityQueue.add(new User("microsoft"));
    priorityQueue.add(new User("zoom"));

    assertNotNull(priorityQueue.peek());
    assertEquals("alibaba", priorityQueue.poll().getUsername());

    assertNotNull(priorityQueue.peek());
    assertEquals("apple", priorityQueue.peek().getUsername());

    assertNotNull(priorityQueue.peek());
    assertEquals("apple", priorityQueue.poll().getUsername());

    assertEquals("[google, microsoft, zoom]", priorityQueue.toString());
  }
}