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| 12. 2. 4. 泛型先进先出 |
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import java.util.AbstractCollection;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
public class QueueTester {
public static void main(String[] args) {
BoundedQueue<String> q = new BoundedQueue<String>(10);
q.add("A");
q.add("B");
q.add("C");
q.remove();
q.add("D");
ArrayList<String> a = new ArrayList<String>();
a.addAll(q);
System.out.println("Result of bulk add: " + a);
System.out.println("Minimum: " + Collections.min(q));
}
}
/**
* A first-in, first-out bounded collection of objects.
*/
class BoundedQueue<E> extends AbstractCollection<E> {
private Object[] elements;
private int head;
private int tail;
private int count;
public BoundedQueue(int capacity) {
elements = new Object[capacity];
count = 0;
head = 0;
tail = 0;
}
public Iterator<E> iterator() {
return new Iterator<E>() {
public boolean hasNext() {
return visited < count;
}
public E next() {
int index = (head + visited) % elements.length;
E r = (E) elements[index];
visited++;
return r;
}
public void remove() {
throw new UnsupportedOperationException();
}
private int visited = 0;
};
}
/**
* Remove object at head.
*
* @return the object that has been removed from the queue
* @precondition size() > 0
*/
public E remove() {
E r = (E) elements[head];
head = (head + 1) % elements.length;
count--;
return r;
}
/**
* Append an object at tail.
*
* @param anObject
* the object to be appended
* @return true since this operation modifies the queue. (This is a
* requirement of the collections framework.)
* @precondition !isFull()
*/
public boolean add(E anObject) {
elements[tail] = anObject;
tail = (tail + 1) % elements.length;
count++;
return true;
}
public int size() {
return count;
}
/**
* Checks whether this queue is full.
*
* @return true if the queue is full
*/
public boolean isFull() {
return count == elements.length;
}
/**
* Gets object at head.
*
* @return the object that is at the head of the queue
* @precondition size() > 0
*/
public E peek() {
return (E) elements[head];
}
}
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