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public class SimpleObjectFIFO extends Object {
private Object[] queue;
private int capacity;
private int size;
private int head;
private int tail;
public SimpleObjectFIFO(int cap) {
capacity = (cap > 0) ? cap : 1; // at least 1
queue = new Object[capacity];
head = 0;
tail = 0;
size = 0;
}
public synchronized int getSize() {
return size;
}
public synchronized boolean isFull() {
return (size == capacity);
}
public synchronized void add(Object obj) throws InterruptedException {
while (isFull()) {
wait();
}
queue[head] = obj;
head = (head + 1) % capacity;
size++;
notifyAll(); // let any waiting threads know about change
}
public synchronized Object remove() throws InterruptedException {
while (size == 0) {
wait();
}
Object obj = queue[tail];
queue[tail] = null; // don't block GC by keeping unnecessary reference
tail = (tail + 1) % capacity;
size--;
notifyAll(); // let any waiting threads know about change
return obj;
}
public synchronized void printState() {
StringBuffer sb = new StringBuffer();
sb.append("SimpleObjectFIFO:\n");
sb.append(" capacity=" + capacity + "\n");
sb.append(" size=" + size);
if (isFull()) {
sb.append(" - FULL");
} else if (size == 0) {
sb.append(" - EMPTY");
}
sb.append("\n");
sb.append(" head=" + head + "\n");
sb.append(" tail=" + tail + "\n");
for (int i = 0; i < queue.length; i++) {
sb.append(" queue[" + i + "]=" + queue[i] + "\n");
}
System.out.print(sb);
}
public static void main(String[] args) {
try {
SimpleObjectFIFO fifo = new SimpleObjectFIFO(5);
fifo.printState();
fifo.add("S01");
fifo.printState();
fifo.add("S02");
fifo.printState();
fifo.add("S03");
fifo.printState();
Object obj = fifo.remove();
System.out.println("just removed obj=" + obj);
fifo.printState();
fifo.add("S04");
fifo.printState();
fifo.add("S05");
fifo.printState();
fifo.add("S06");
fifo.printState();
} catch (InterruptedException x) {
x.printStackTrace();
}
}
}
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