阅读以下技术说明和Java代码，将Java程序中(1)～(5)空缺处的语句填写完整。

[说明]

类Queue表示队列，类中的方法如表4-12所示。

类Node表示队列中的元素；类EmptyQueueException给出了队列中的异常处理操作。

[Java代码]

public class testmain { //主类

public static viod main (string args[]) {

Queue q= new Queue;

q.enqueue("first!");

q.enqueue("second!");

q.enqueue("third!");

(1) {

while(true)

system.out.println(q.dequeue());

}

catch( (2) ) { }

}

public class Queue { //队列

node m_firstnode;

public Queue(){m_firstnode=null;}

public boolean isempty() {

if (m_firstnode= =null)

return true;

else

return false;

}

public viod enqueue(object newnode) { //入队操作

node next = m_firstnode;

if (next = = null) m_firstnode=new node(newnode);

else {

while(next.getnext() !=null)

next=next.getnext();

next.setnext(new node(newnode));

}

}

public object dequeue() (3) { //出队操作

object node;

if (is empty())

(4)

else {

node =m_firstnode.getobject();

m_firstnode=m_firstnode.getnext();

return node;

}

}

}

public class node{ //队列中的元素

object m_data;

node m_next;

public node(object data) {m_data=data; m_next=null;}

public node(object data,node next) {m_data=data; m_next=next;}

public void setobject(object data) {m_data=data; }

public object getobject(object data) {return m_data; }

public void setnext(node next) {m_next=next; }

public node getnext() {return m_next; }

}

public class emptyqueueexception extends (5) { //异常处理类

public emptyqueueexception() {

system. out. println ( "队列已空!" );

}

}