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先进先出的队列

摘要: 先进先出的队列

</td> </tr> <tr> <td width="486" height="35" valign="top" class="ArticleTeitle"> public class SimpleObjectFIFO extends Object {
private Object[] queue; private int capacity;//队列容量
private int size;//队列的大小
private int head;//队列的当前项
private int tail;//下一个添加项的索引

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);
}
}
测试代码：
public class SimpleObjectFIFOTest extends Object {
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();
}
}
}

程序运行结果：

C:\java>java SimpleObjectFIFOTest
SimpleObjectFIFO:
capacity=5
size=0 - EMPTY
head=0
tail=0
queue[0]=null
queue[1]=null
queue[2]=null
queue[3]=null
queue[4]=null
SimpleObjectFIFO:
capacity=5
size=1
head=1
tail=0
queue[0]=S01
queue[1]=null
queue[2]=null
queue[3]=null
queue[4]=null
SimpleObjectFIFO:
capacity=5
size=2
head=2
tail=0
queue[0]=S01
queue[1]=S02
queue[2]=null
queue[3]=null
queue[4]=null
SimpleObjectFIFO:
capacity=5
size=3
head=3
tail=0
queue[0]=S01
queue[1]=S02
queue[2]=S03
queue[3]=null
queue[4]=null
just removed obj=S01
SimpleObjectFIFO:
capacity=5
size=2
head=3
tail=1
queue[0]=null
queue[1]=S02
queue[2]=S03
queue[3]=null
queue[4]=null
SimpleObjectFIFO:
capacity=5
size=3
head=4
tail=1
queue[0]=null
queue[1]=S02
queue[2]=S03
queue[3]=S04
queue[4]=null
SimpleObjectFIFO:
capacity=5
size=4
head=0
tail=1
queue[0]=null
queue[1]=S02
queue[2]=S03
queue[3]=S04
queue[4]=S05
SimpleObjectFIFO:
capacity=5
size=5 - FULL
head=1
tail=1
queue[0]=S06
queue[1]=S02
queue[2]=S03
queue[3]=S04
queue[4]=S05

C:\java>

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</td> </tr> <tr> <td height="25" colspan="2" valign="top" class="ArticleTeitle">

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