Question

我正在建造一个铁路模拟器，包括模拟器，车站，火车，路线和乘客。我将路由对象作为参数传递给火车对象时遇到了问题 - 它一直是空的。我已将我的代码作为解释问题的最佳方式。

import java.util.ArrayList;

public class Simulator {
int numStations;    
Route route1;
ArrayList<Station> stations;
ArrayList<Train> trains;
Route[] routes;

public static void main(String[] args) {

    //set up network
    Simulator sim = new Simulator();                
    ArrayList<Station> stations = new ArrayList<Station>();
    stations = sim.generateStations();
    Route[] routes;
    routes = sim.generateRoutes(stations);
    System.out.println("Route array " + routes);
    ArrayList<Train> trains = new ArrayList<Train>();
    trains = sim.generateTrains(routes);

    //start simulator
    sim.generatePassengers(stations);
    Train currentTrain = trains.get(0);
    System.out.println("current train " + currentTrain);
    //route null here
    System.out.println("Route of current train " + currentTrain.route);


}


public Route[] generateRoutes(ArrayList<Station> stations){
    //initialise routes between stations

    Station[] stationList1 = {stations.get(0), stations.get(1), stations.get(2), stations.get(3), stations.get(4), stations.get(5)};
    int[] stationDist1 = {200,100,200,300,200,300};
    Route route1 = new Route(true, stationList1, stationDist1);
    System.out.println("route1 " + route1);

    //make list of all routes
    Route[] routeList;  
    routeList = new Route[1];
    routeList[0] = route1;

    return routeList;
}

public ArrayList<Train> generateTrains(Route[] routes){
    //initialise trains
    ArrayList<Train> trainList = new ArrayList<Train>();
    trainList.add(new Train(routes[0], 100, 0, true, 5));
    trainList.add(new Train(routes[0], 100, 4, false, 10));

    System.out.println("first train in list " + trainList.get(0));
    System.out.println("first route in array " + routes[0]);
    //route is null here
    System.out.println("route of first train " + (trainList.get(0)).route);

    return trainList;
}
}

这是我的输出：

route1 Route @ addbf1

路线阵列[LRoute; @ 42e816

阵列Route @ addbf1
中的Route1
列车中的第一列火车@ 190d11

数组Route @ addbf1
中的第一个路由
第一列火车的路线

目前的火车列车@ 190d11

当前列车的路线为空

有谁可以解释我哪里出错？

编辑：火车类声明：

public class Train {
Route route;
int capacity;
int recentLoc;
boolean forwards;
boolean atStation;
int speed;
Train currentTrain;
int timeAtStation;

//train constructor
public Train(Route r, int c, int i, boolean f, int s){
    r = route;
    c = capacity;
    i = recentLoc;
    f = forwards;
    s = speed;
    atStation = true;
    timeAtStation = 0;
}

Answer 1

您没有为实例变量赋值。 object的默认值为null。在Train构造函数中将“r = route”更改为“route = r”（所有其他字段都相同）。

public class Train {
Route route;
int capacity;
int recentLoc;
boolean forwards;
boolean atStation;
int speed;
Train currentTrain;
int timeAtStation;

//train constructor
public Train(Route r, int c, int i, boolean f, int s){
    route = r;
    capacity = c;
    recentLoc = i;
    forwards = f;
    speed = s;
    atStation = true;
    timeAtStation = 0;
}

Answer 2

route = r; 
capacity = c;

等

Answer 3

您的输出中有三个问题。

首先，当你想要为数组打印conntent时，你必须遍历它的元素，否则你只需要打印内存地址。为了帮助你解决hava API的方法：

Arrays.toString(Object[]);

同样的问题在你的Train中，你没有覆盖toString()方法，这就是为什么Java打印它的地址，因为这是它的默认行为。

尝试将此方法添加到路由类中，看看会发生什么，

@Override
public String toString(){
   return "This is message from rout"    
}

Ant在火车的构造中最后一次

您将参数分配给变量。你应该反过来。

public Train(Route r, int c, int i, boolean f, int s){
    this.route = r;
    this.capacity = c;
    this.recentLoc = i;
    this.forwards = f;
    this.speed = s;
    this.atStation = true;
    this.timeAtStation = 0;
}

Answer 4

这些作业应该是相反的，左边的东西是分配的东西。

r = route;
c = capacity;
i = recentLoc;
f = forwards;
s = speed;

应该是

 route = r;
   capacity = c;
   recentLoc = i;
    forwards = f;
    speed = s;

Answer 5

你的作业错误。

r = route;

这意味着route的值将分配给r。

将构造函数更改为以下内容：

public Train(Route r, int c, int i, boolean f, int s)
{     
     route = r;;     
     capacity = c;;     
     recentLoc = i;     
     forwards = f;     
     speed = s;     
     atStation = true;     
     timeAtStation = 0; 
}

将对象作为参数传递给其他对象 - null

5 个答案: