Queue操作,該項提交WA,不知原因

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class Queue {

static int[] queue;
static int head = 0;
static int tail = 0;

public static void main(String[] args) throws FileNotFoundException {
    // TODO Auto-generated method stub
    Scanner sc = new Scanner(System.in);
    sc = new Scanner(new File("src/file/queue"));
    char[] opera = new char[20];
    while (sc.hasNext()) {
        int T = sc.nextInt();
        queue = new int[2 * T];
        for (int i = 0; i < T; i++) {
            opera = sc.next().toCharArray();
            switch (opera[0]) {
            case 'e':
                int tmp = sc.nextInt();
                enqueue(tmp);
                break;
            case 'd':
                dequeue();
                break;
            case 'q':
                query();
                break;
            }
        }
        System.out.println();
    }
}

public static void enqueue(int tmp) {
    queue[tail++] = tmp;
}

public static void dequeue() {
    if (tail == head) {
        System.out.println("this is empty!");
    } else {
        System.out.println(queue[head++]);
    }
}

public static void query() {
    if (head == tail) {
        System.out.println("this is empty!");
    } else {
        for (int i = head; i < tail; i++) {
            System.out.println(queue[i]);
        }
        head = tail = 0;
    }
}

}

sample input:
10
enqueue 1
enqueue 2
enqueue 3
enqueue 4
query
dequeue
enqueue 1
dequeue
query
dequeue
30
enqueue 1
enqueue 2
enqueue 3
enqueue 4
enqueue 1
enqueue 2
enqueue 3
enqueue 4
enqueue 1
enqueue 2
enqueue 3
enqueue 4
enqueue 1
enqueue 2
enqueue 3
enqueue 4
enqueue 1
enqueue 2
enqueue 3
enqueue 4
enqueue 1
enqueue 2
enqueue 3
enqueue 4
enqueue 1
enqueue 2
enqueue 3
enqueue 4
enqueue 1
query