Question

I am writing an App for Android where I allow users to create their vehicles, which I store to a config file in a structured format. Something like:

[VEHICLE1]
VEHICLE1>type>car
VEHICLE1>fuelUsageMPG>30
VEHICLE1>speed>100
[ENDVEHICLE1]
[VEHICLE2]
VEHICLE2>type>car
VEHICLE2>fuelUsage>35
VEHICLE2>speed>85
[ENDVEHICLE2]

My App has a class named "vehicle" with the same fixed number of attributes. So what I am trying to do is to create those objects at run-time and set the object properties based on the config file so that I can then use further along in the program to perform calculations.

I parse that config file using flags and referencing groups and cycle through as many times as I find the pattern "[VEHICLE.]" but cannot figure out how to create an instance of vehicles() using VEHICLE1, VEHICLE2 or any other automated incremental object reference.

Any sample code or guidance would be much appreciated.

Answer 1

At first, you can simplify your your config file like this:

[VEHICLE1]
    type>car
    fuelUsageMPG>30
    speed>100
[ENDVEHICLE1]
[VEHICLE2]
    type>car
    fuelUsage>35
    speed>85
[ENDVEHICLE2]`

(but I think using a JSON or XML will be easier, as you will not have to use your own parser)

then you can just read from this file vehicle by vehicle and call a constructor of your vehicles for each of them.

Something like: new Vehicle(type, fuelUsage, speed)

EDIT:

You can store them like that:

ArrayList al = new ArrayList();

..... loop start
al.add(new Vehicle(type, fuelUsage, speed));
..... loop end

//get the VEHICLE1
al.get(0);
//get the VEHICLE5
al.get(4);

Answer 2

我也完全同意Andrii和ElDuderino，但是如果您无法更改输入格式。您可以尝试以下代码：

如下所示，请使用方法说getVehicleList：

public ArrayList<Vehicle> getVehicleList(File fin) {
    ArrayList<Vehicle> vehicleList = new ArrayList<Vehicle>();

    // Taken for my convenience, you should read it from "File fin"
    InputStream ins = getResources().openRawResource(
            getResources().getIdentifier("raw/vehicle", "raw", getPackageName()));
    try {
        BufferedReader br = new BufferedReader(new InputStreamReader(ins));
        String line = null;

        int cursor = 0;
        while ((line = br.readLine()) != null) {
            if (line.contains("[VEHICLE")) {
                Vehicle v = new Vehicle();
                vehicleList.add(cursor, v);
            } else if (line.contains("[ENDVEHICLE")) {
                cursor++;
            } else {
                // read vehicle attributes here
                Vehicle v1 = vehicleList.get(cursor);
                String[] attr = line.split(">");
                if (attr != null && attr.length == 3) {
                    if (attr[1].contains("type")) {
                        v1.type = attr[2];
                    } else if (attr[1].contains("fuelUsage")) {
                        v1.fuelUsageMPG = attr[2];
                    } else if (attr[1].contains("speed")) {
                        v1.speed = attr[2];
                    }
                }
            }
        }
        return vehicleList;
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

请问会有很多边缘情况，但您的想法是必须创建ArrayList，直到您阅读相同的Vehicle，保持cursor相同并阅读相同的Vehicle 1}}来自cursor的{{1}}位置。

creating objects at runtime from a config file in Java

2 个答案: