Java中是否允许使用以下代码？我的程序不起作用，除非我评论这一行，我不确定是否多重＆amp;＆amp; if中的语句是允许的。
if(number.isBusy() && number2.isBusy() && number3.isBusy() && number4.isBusy() && number5.isBusy() ) {}
编辑添加： 如果你注释掉上面给出的那一行，那么程序实际上会在输出窗口中显示一些东西（虽然唯一能够添加东西的东西是“number5”）如果它被留下，所有的输出都是零。
这是现在的整个计划：
// FILE: Line.java
// This program illustrates the use of the lineSimulate method which uses
// a simple queue to simulate cars waiting at a car wash.
import java.util.LinkedList;
import java.util.Queue;
import java.util.Scanner;
// import edu.colorado.simulations.BooleanSource;
// import edu.colorado.simulations.Line ;
// import edu.colorado.simulations.Averager;
/******************************************************************************
* The <CODE>CarWash</CODE> Java application illustrates the use of
* the <CODE>lineSimulate</CODE> method.
* The illustration uses the following values:
* <CODE>
* <br>lineTime = 240
* <br>arrivalTime = 0.0025
* <br>totalTime = 6000
* </CODE>
*
* <p><dt><b>Java Source Code for this class:</b><dd>
* <A HREF="../applications/CarWash.java">
* http://www.cs.colorado.edu/~main/applications/CarWash.java
* </A>
*
* @author Michael Main
* <A HREF="mailto:main@colorado.edu"> (main@colorado.edu) </A>
*
* @version
* Jun 12, 1998
******************************************************************************/
public class LineWait
{
/**
* The main method activates <CODE>lineSimulate</CODE> with the values:
* <CODE>
* <br>lineTime = 240
* <br>arrivalTime = 0.0025
* <br>totalTime = 6000
* </CODE>
* <BR>The <CODE>String</CODE> argument (<CODE>args</CODE>) is not used in
* this implementation.
**/
public static void main(String[ ] args)
{
final int LINETIME = 100 + (int)(Math.random() * ((400) + 1));
final double ARRIVALPROB = (Math.random() * ((.1) + 1));
final int TOTALTIME = 6000;
lineSimulate(LINETIME, ARRIVALPROB, TOTALTIME);
}
/**
* Simulate the running of a car washer for a specified amount of time.
* @param <CODE>lineTime</CODE>
* the number of seconds required to wash one car
* @param <CODE>arrivalProb</CODE>
* the probability of a customer arriving in any second, for example
* 0.1 is 10%
* @param <CODE>totalTime</CODE>
* the total number of seconds for the simulation
* <dt><b>Precondition:</b><dd>
* <CODE>lineTime</CODE> and <CODE>totalTime</CODE> are positive;
* <CODE>arrivalProb</CODE> lies in the range 0 to 1.
* <dt><b>Postcondition:</b><dd>
* The method has simulated a car wash where <CODE>lineTime</CODE> is the
* number of seconds needed to wash one car, <CODE>arrivalProb</CODE> is
* the probability of a customer arriving in any second, and
* <CODE>totalTime</CODE> is the total number of seconds for the
* simulation. Before the simulation, the method has written its three
* parameters to <CODE>System.out</CODE>. After the simulation, the method
* has written two pieces of information to <CODE>System.out</CODE>:
* (1) The number of cars washed, and (2) The average waiting time for
* customers that had their cars washed. (Customers that are still in the
* queue are not included in this average).
* @exception java.lang.IllegalArgumentException
* Indicates that one of the arguments violates the precondition.
**/
public static void lineSimulate
(int lineTime, double arrivalProb, int totalTime)
{
Queue<Integer> arrivalTimes = new LinkedList<Integer>( );
Queue<Integer> arrivalTimes2 = new LinkedList<Integer>( );
Queue<Integer> arrivalTimes3 = new LinkedList<Integer>( );
Queue<Integer> arrivalTimes4 = new LinkedList<Integer>( );
Queue<Integer> arrivalTimes5 = new LinkedList<Integer>( );
int next;
BooleanSource arrival = new BooleanSource(arrivalProb);
Line number = new Line(lineTime);
Line number2 = new Line(lineTime);
Line number3 = new Line(lineTime);
Line number4 = new Line(lineTime);
Line number5 = new Line(lineTime);
Averager waitTimes = new Averager( );
Averager waitTimes2 = new Averager();
Averager waitTimes3 = new Averager();
Averager waitTimes4 = new Averager();
Averager waitTimes5 = new Averager();
int currentSecond;
// Write the parameters to System.out.
System.out.println("Seconds to wait in line " + lineTime);
System.out.print("Probability of customer arrival during a second: ");
System.out.println(arrivalProb);
System.out.println("Total simulation seconds: " + totalTime);
// Check the precondition:
if (lineTime <= 0 || arrivalProb < 0 || arrivalProb > 1 || totalTime < 0)
throw new IllegalArgumentException("Values out of range");
for (currentSecond = 0; currentSecond < totalTime; currentSecond++)
{ // Simulate the passage of one second of time.
// Check whether a new customer has arrived.
if (arrival.query( ))
{
System.out.println("Test1");
if(number.isBusy() && number2.isBusy() && number3.isBusy() && number4.isBusy() && number5.isBusy() )
{
System.out.println("Test2");
if(arrivalTimes.size() < arrivalTimes2.size() && arrivalTimes.size() < arrivalTimes3.size() && arrivalTimes.size() < arrivalTimes4.size() && arrivalTimes.size() < arrivalTimes5.size())
{
arrivalTimes.add(currentSecond);
System.out.println("Test");
}
else if(arrivalTimes2.size() < arrivalTimes.size() && arrivalTimes2.size() < arrivalTimes3.size() && arrivalTimes2.size() < arrivalTimes4.size() && arrivalTimes2.size() < arrivalTimes5.size())
{
arrivalTimes2.add(currentSecond);
System.out.println("Test");
}
else if(arrivalTimes3.size() < arrivalTimes.size() && arrivalTimes3.size() < arrivalTimes2.size() && arrivalTimes3.size() < arrivalTimes4.size() && arrivalTimes3.size() < arrivalTimes5.size())
{
arrivalTimes3.add(currentSecond);
System.out.println("Test");
}
else if(arrivalTimes4.size() < arrivalTimes.size() && arrivalTimes4.size() < arrivalTimes3.size() && arrivalTimes4.size() < arrivalTimes2.size() && arrivalTimes4.size() < arrivalTimes5.size())
{
arrivalTimes4.add(currentSecond);
System.out.println("Test");
}
else{arrivalTimes5.add(currentSecond);}
}
}
// Check whether we can put the person into a line.
if ((!number.isBusy( )) && (!arrivalTimes.isEmpty( )))
{
next = arrivalTimes.remove( );
waitTimes.addNumber(currentSecond - next);
number.startMoving( );
}
if ((!number2.isBusy( )) && (!arrivalTimes2.isEmpty( )))
{
next = arrivalTimes2.remove( );
waitTimes2.addNumber(currentSecond - next);
number2.startMoving( );
}
if ((!number3.isBusy( )) && (!arrivalTimes3.isEmpty( )))
{
next = arrivalTimes3.remove( );
waitTimes3.addNumber(currentSecond - next);
number3.startMoving( );
}
if ((!number4.isBusy( )) && (!arrivalTimes4.isEmpty( )))
{
next = arrivalTimes4.remove( );
waitTimes4.addNumber(currentSecond - next);
number4.startMoving( );
}
if ((!number5.isBusy( )) && (!arrivalTimes5.isEmpty( )))
{
next = arrivalTimes5.remove( );
waitTimes5.addNumber(currentSecond - next);
number5.startMoving( );
}
// Subtract one second from the remaining time in the current li
number.reduceRemainingTime( );
number2.reduceRemainingTime( );
number3.reduceRemainingTime( );
number4.reduceRemainingTime( );
number5.reduceRemainingTime( );
}
// Write the summary information about the simulation.
System.out.println("\nCustomers served Line1: " + waitTimes.howManyNumbers( ));
if (waitTimes.howManyNumbers( ) > 0)
System.out.println("Average wait Line1: " + waitTimes.average( ) + " sec");
System.out.println("\nCustomers served Line2: " + waitTimes2.howManyNumbers( ));
if (waitTimes.howManyNumbers( ) > 0)
System.out.println("Average wait Line2: " + waitTimes2.average( ) + " sec");
System.out.println("\nCustomers served Line3: " + waitTimes3.howManyNumbers( ));
if (waitTimes.howManyNumbers( ) > 0)
System.out.println("Average wait Line3: " + waitTimes3.average( ) + " sec");
System.out.println("\nCustomers served Line4: " + waitTimes4.howManyNumbers( ));
if (waitTimes.howManyNumbers( ) > 0)
System.out.println("Average wait Line4: " + waitTimes4.average( ) + " sec");
System.out.println("\nCustomers served Line5: " + waitTimes5.howManyNumbers( ));
if (waitTimes.howManyNumbers( ) > 0)
System.out.println("Average wait Line5: " + waitTimes5.average( ) + " sec");
}
}
答案 0 :(得分：7)
表达式是完全合法的语法。 &&运算符是一个短路逻辑AND：评估从左到右进行，并将在第一个项（如果有的话）停止，评估为false。
修改
根据您的修改，我猜测问题是if的正文只有在number的全部时才会输入。 。 。，number5很忙。 （这只是猜测，因为你没有发布Line类看起来像什么，或者你想要看到的行为。
作为旁注，我认为如果您定义了一个封装了Queue，Line和Averager的类，那么您的程序将更具可读性（并且可维护性）。 （据推测，这三个对象组合在一起构成了对你的问题域有意义的东西。）然后你可以声明这些对象的数组（或者，更好的是List）并使用它们而不是独立地使用它们变量
答案 1 :(得分：2)
是的，可以将有效数量的逻辑运算符链接在一起。
答案 2 :(得分：0)
是的，这是允许的。和＆amp;＆amp;是短路运算符，因此一旦其中一个谓词失败，就不会进行进一步的评估。如果您想要评估所有条件，您可以使用＆amp; （即只有一个＆符号）并且将评估所有谓词。想要这样做的主要原因是谓词是否存在您想要发生的副作用。这通常是不好的做法，但在你的情况下，它看起来就像你想要的那样......
if (number.isBusy() &
number2.isBusy() &
number3.isBusy() &
number4.isBusy() &
number5.isBusy()) {
}
每个isBusy()都将执行，结果将是返回值的AND。
if (number.isBusy() &&
number2.isBusy() &&
number3.isBusy() &&
number4.isBusy() &&
number5.isBusy()) {
}
每个isBusy()将执行，直到一个失败，将不会调用以下isBusy()。
答案 3 :(得分：0)
user1247751应提供更多信息以获得更好的答案。
但是，根据提供的信息，我可以推测其中一个isBusy方法会更改系统的状态，使其无效。