Java Reflection Dealing with Arrays

Question

I am using reflection and recursion to find the fields within a class. The issue is, an object that I have (PointCloud) has 2 fields in it: an int Timestamp and an array of 4 of type (LidarLayerTag).

When I try to get the field.getName() on the array element, it returns back an list type [Lcom.joy.fb20.dds.LidarLayerTag instead of what I would expect being the non-list version.

Below is the code that I am using to recursively go through the object types. I trimmed out the other types leaving only the portion dealing with arrays since that is where the issue lies. Any ideas as to how to properly deal with getting a single element of the array instead of the list type?

I wanted something a bit more elegant than just replacing the "[L" at the beginning of the string that I'm sending through the recursion but I can do that if worst comes to worst.

public ArrayList<String> processIDLData(String topicName, String parentFieldName, Integer count)
    {
        Field[] fieldList = null;
        String query = "";
        ArrayList<String> layout = new ArrayList<String>();

        try
        {
            fieldList = Class.forName(topicName).getDeclaredFields();

            for (Field a : fieldList)
            {
               if (a.getType().isArray() && ((a.getType().getName().startsWith("["))))
                    {

                        // Dealing with primitive arrays
                        if (a.getType().getName().equals("[F"))
                        {
                            errorLog.error("Array of Floats = " + a.getName());
                            // Arrays of floats
                            for (int i = 0; i < Array.getLength(a.get(Class.forName(topicName).getConstructor().newInstance())); i++)
                            {
                                layout.add(a.getName() + "[" + i + "]");
                            }
                        } else if (a.getType().getName().equals("[Ljava.lang.String;"))
                        {
                            errorLog.error("Array of Strings = " + a.getName());
                            // Arrays of Strings
                            for (int i = 0; i < Array.getLength(a.get(Class.forName(topicName).getConstructor().newInstance())); i++)
                            {
                                layout.add(a.getName() + "[" + i + "]");
                            }
                        } else if (a.getType() == int[].class || a.getType() == double[].class || a.getType() == short[].class || a.getType() == char[].class || a.getType() == byte[].class
                                || (com.rti.dds.util.Enum.class.isAssignableFrom(Class.forName(a.getType().getName().replace(";", "").replace("[L", "")))))
                        {
                            errorLog.error("Array of Primitives = " + a.getName());
                            // Arrays of ints, shorts, bytes, longs, chars, or enums
                            for (int i = 0; i < Array.getLength(a.get(Class.forName(topicName).getConstructor().newInstance())); i++)
                            {
                                layout.add(a.getName() + "[" + i + "]");
                            }
                        } else
                        {
                            errorLog.error("Array of Objects = " + a.getName() + " " + a.getType().getName());
                            if (count == null || count == 0)
                            {
                                // Arrays of objects
                                for (int i = 0; i < Array.getLength(a.get(Class.forName(topicName).getConstructor().newInstance())); i++)
                                {
                                    layout.addAll(processIDLData(a.getType().getName(), a.getName(), i));
                                }
                            } else
                            {
                                for (int i = 0; i < Array.getLength(a.get(Class.forName(topicName).getConstructor().newInstance())); i++)
                                {
                                    layout.addAll(processIDLData(a.getType().getName(), a.getName() + "[" + count + "]", i));
                                }
                            }
                        }
                    }

        return layout;
    }

You get paid by the line I am guessing, eh? haha

Ascalonian
– Ascalonian

2018-04-24 14:43:26 +00:00
Commented Apr 24, 2018 at 14:43 — Ascalonian
– Ascalonian, Commented Apr 24, 2018 at 14:43

Joop Eggen · Accepted Answer · 2018-04-24 14:40:40Z

1

For that there is the Class.getComponentType():

Field a; ...
if (a.getType().isArray()) {
    Class<?> elementType = a.getComponentType();
    if (elementType == float.class) { ... // float[]
        ... elementType.getSimpleName() ...;
    }
}

Recurse on the component type and do something with the result, adding "[]" or such.

answered Apr 24, 2018 at 14:40

Joop Eggen

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1 Comment

Tacitus86 Over a year ago

Flawless. Thank you!

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