接口
public interface Queue<E> {
int getSize();
boolean isEmpty();
void enqueue(E e);
E dequeue();
E getFront();
}
实现类
public class LoopQueue<E> implements Queue<E>{
private E[] data;
private int front, tail;
private int size;
public LoopQueue(int capacity){
data = (E[])new Object[capacity+1];
front = 0;
tail = 0;
size = 0;
}
public LoopQueue(){
this(10);
}
public getCapacity(){
return data.length - 1;
}
@Override
public boolean isEmpty(){
return tail == front;
}
@Override
public int getSize(){
return size;
}
@Override
public void enqueue(E e){
if((tail + 1) % data.length == front){
resize(getCapacity * 2);
}
}
@Override
public E dequeue(){
if (isEmpty()){
throw new IllegalArgumentException("Cannot dequeue from an empty queue");
}
E ret = data[front];
data[front] = null;
front = (front + 1) % data.length;
size --;
if (size < getCapacity() / 4 && getCapacity() / 2 != 0){
resize(getCapacity);
}
}
@Override
public E getFront(){
if (isEmpty()){
throw new IllegalArgumentException("Queue is empty");
}
return data[front];
}
public void resize(int newCapacity){
E[] newData = (E[])new Object(newCapacity);
for(int i = 0; i < size; i++ ){
newData[i] = data[(i + front) % data.length];
}
data = newData;
front = 0;
tail = size;
}
@Override
public String toString(){
StringBuilder res = new StringBuilder();
res.append(String.format("Queue: size = %d , capacity = %d\n", size, getCapacity()));
res.append("front [");
for(int i = front ; i != tail ; i = (i + 1) % data.length ){
res.append(data[i]);
if((i+1) % data.length != tail)
res.append(", ");
}
res.append("] tail");
return res.toString();
}
}
测试类
public static void main(String[] args) {
LoopQueue<Integer> queue = new LoopQueue<>();
for(int i = 0 ; i < 10 ; i ++){
queue.enqueue(i);
System.out.println(queue);
if(i % 3 == 2){
queue.dequeue();
System.out.println(queue);
}
}
}