CODEWITHSUNDEEP
javagenericsinstantiation
Mockarutan
Mockarutan

Reputation: 442

InstantiationException when Instantiate generic type in java

I have been trying to get this to work for a while and I have searched high and low for answers (including here). But I can't figure it out.

So here the code (a bit minimized):

public class Event<T> {
    public MessageType msgType;
    public int layer;
    public int gameObjectId;
    public String name;
    public float value;
    public int senderId;
    public T ext;

    public Event(Class<T> classType) {
        if(classType != null) {
            try {
                ext = classType.newInstance();  //this is the failing line
            } catch (InstantiationException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        }
        msgType = MessageType.NONE;
        layer = TypeHandler.lAll;
        gameObjectId = -1;
        name = null;
        value = -1;
    }
}

public class DataExtension {
    public float[] values;
    public String[] string;
    public Object[] objects;
    public boolean[] boolens;
}

This is the problem:

Event<DataExtension> mSelectionEvent;

mSelectionEvent = new Event<DataExtension>(DataExtension.class, MessageType.SELECTED);

This give me the following exception: 

java.lang.InstantiationException: se.plainentertainment.bagl.v2.core.Event$DataExtension
    at java.lang.Class.newInstance0(Unknown Source)
    at java.lang.Class.newInstance(Unknown Source)
    at se.plainentertainment.bagl.v2.core.Event.<init>(Event.java:85)
    at se.plainentertainment.bagl.v2.core.SelectionHandler.<init>(SelectionHandler.java:46)...

So, the class that I'm trying to instantiate should meet all the requirements, right? It has a default constructor and it's not abstract in any way. Why do I get this error?

Thanks in advance!

Upvotes: 0

Views: 608

Answers (1)

James
James

Reputation: 8586

Event$DataExtension

This is an inner class. Is it static? I'm going to go with a hunch and say no. Which means it contains a reference to the containing Event (implicitly), which means you likely can't instantiate it via newInstance.

Try setting it to be a static inner class, or move it out of the class it if it doesn't need to be tied to the event object.

Upvotes: 1

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