Queue操作,该项提交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