Queueの実装

TestQueue.java

import java.util.*;
import org.junit.*;
import static org.junit.Assert.*;

// First In First Out
public class TestQueue {
  @Test
  public void testQueue(){
    Queue<String> q = new Queue<String>();
    q.enqueue("0");
    q.enqueue("1");
    assertEquals("0", q.dequeue());
  }

  @Test
  public void testQueue2(){
    Queue<String> q = new Queue<String>();
    q.enqueue("0");
    q.enqueue("1");
    q.enqueue("2");
    q.dequeue();
    assertEquals(2, q.size());
  }
}

class Queue<E> {
  static class Node<E> {
    E data;
    Node<E> next = null;
  }

  Node<E> first, last;

  void enqueue(E e){
    Node<E> node = new Node<E>();
    node.data = e;
    if(first == null){
      first = node;
      last = first;
    } else {
      last.next = node;
      last = node;
    }
  }

  E dequeue(){
    if(first == null){
      return null;
    }
    E obj = first.data;
    first = first.next;
    return obj;
  }

  int size(){
    if(first == null){
      return 0;
    }
    int length = 1;
    Node<E> node = first;
    while(node.next != null){
      length++;
      node = node.next;
    }
    return length;
  }
}