Question

嘿伙计们，我正在计算机科学课上完成最后一个项目。它将是一个非常简单的航空系统实时模拟。我刚开始，所以大多数仍然是占位符代码，它仍然没有注释和可怕所以不要太苛刻，但我得到一个非常奇怪的空指针异常错误。我已经在输出中添加了调试行，所以你可以看到它发生了。

您可以立即获取源代码here。

基本上，类fileManager（）以递归方式循环遍历文件夹并查找所有.inis并将它们放在链接列表中。然后，renderingArea（）的构造函数根据.inis的＃和它们的默认值填充city []。当我尝试将文件plane.ini的位置作为InputStream传递给类plane（）的构造函数时，我得到一个空指针异常错误。有人可以帮忙吗？

class renderingArea extends JPanel {

public fileManager files;   
public city[] cities;

public renderingArea(){ 

            //  ... other code

    for( loop through all files in fileManager ){
        File current = files.ini.get(i);
        if(current.getName().contains("city")){
            try{
                InputStream cityStream = files.getResource(current.getName());
                InputStream planeStream = files.getResource("plane.ini");
                cities[index] = new city( cityStream, planeStream);
                cityStream.close();
                planeStream.close();
                index++;
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
    for( city current : cities){
        current.setCities(cities);
    }       
}

//  ============== Class City ========================

public class city {
private final String[] keys = {"x","y","name","population","planes_in_hanger"};

public float x;
public float y;
public int population;
public String name;
private Queue<passenger>[] waiting_passengers;  // queue[] parallel to cities.
private Queue<plane> planes_in_hanger;          // a queue is a first in first out ADT. Standard ops apply
private city[] cities;

private IniReader ini;

public city(InputStream inStream, InputStream inStreamPlane) throws IOException, FileNotFoundException {
    System.out.println("city: " + inStream.toString());
    System.out.println("plane: " + inStreamPlane.toString());

    ini = new IniReader();
    ini.load(inStream);

            // .... Other Code

    if(ini.properties.containsKey("planes_in_hanger")){
        try{
            for( int i = 0; i < Integer.parseInt(ini.properties.getProperty("planes_in_hanger")); i++){
                System.out.println("iter: "+i);
                System.out.println("plane: "+inStreamPlane.toString());
                planes_in_hanger.enqueue(new plane(inStreamPlane));
            }
        } catch (NumberFormatException e) {
            e.printStackTrace();
        }
    }
    }

public class plane {
private final String[] keys = {"x","y","max_velocity","passengers"};

public float x;
public float y;
public float max_velocity;
private float x_velocity;
private float y_velocity;
public city destination;
private passenger[] passengers;
public int max_passengers;

private IniReader ini;

    //====================== CLASS PLANE ======================

public plane(InputStream inStream) throws IOException, FileNotFoundException{
    ini = new IniReader();
    ini.load(inStream);

            //rest doesn't matter
}

输出中：

//调试内容，切换到异常

java.lang.NullPointerException
    at city.(city.java:72)
    at renderingArea.(flight_optimizer.java:70)
    at flight_optimizer_GUI.(flight_optimizer.java:103)
    at flight_optimizer.main(flight_optimizer.java:37)
Exception in thread "main" java.lang.NullPointerException
    at renderingArea.(flight_optimizer.java:80)
    at flight_optimizer_GUI.(flight_optimizer.java:103)
    at flight_optimizer.main(flight_optimizer.java:37)

Answer 1

您似乎没有在任何地方初始化新的planes_in_hanger，但您将其声明在顶部。这可能是你的问题？

private Queue<plane> planes_in_hanger = new Queue<plane>();

或者你可以用该方法初始化它。

InputStreams的奇怪空指针异常

1 个答案: