Get subclass from Generic method in Java

Question

I'm trying to write a curious method:

Map<Class, AbstractTool> ToolMap = new HashMap<Class, AbstractTool>(); //init'd correctly @SuppressWarnings("unchecked") public <T extends AbstractTool> T getTool(Class cls){ if (ToolMap.containsKey(cls)) { return (T) ToolMap.get(cls); } else return null; }

In a weird twist of events, this code actually does what I need it to do. My main issue is the fact that in order to call it, i have to make these big calls:

this.getTool<ToolType>(ToolType.class);

Not Cool.

Is there a way to write this method so that it has the following signature?:

ToolType t = this.getTool<ToolType>();

or this one

ToolType t = this.getTool(ToolType); // This one seems impossible without casting.

Affe · Accepted Answer · 2014-05-09 02:28:53Z

The first one won't work because you're looking up a type at runtime, so that parameter is gone. The second one works fine if you just fix your method declaration. Class is a parameterized type that you declared raw.

If you do:

 Map<Class<? extends AbstractTool>, AbstractTool> ToolMap = new HashMap<Class<? extends AbstractTool>, AbstractTool>(); @SuppressWarnings("unchecked") public <T extends AbstractTool> T getTool(Class<T> cls){ if (ToolMap.containsKey(cls)) { return (T) ToolMap.get(cls); } else return null; }

Then you can do:

ToolType t = this.getTool(ToolType.class);

And since you have cls, it's probably worth using it to make a checked cast which will get rid of the warning (return cls.cast(ToolMap.get(cls)))
Thank you kindly. Even though C# and java are quite similar, these little minutia always get me.

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