Passing a class type to a method, then casting to that type?

Question

I'm still pretty new to Java, so I might be missing something obvious here.

I have the following code that I use to pick class types from a list of all my entities:

public Array<?> PickEntities(Class<?> cls) { Array<? super SpriteEntity> allEntities = new Array<Object>(); for (SpriteEntity entity : MyGame.AllEntities) { if (entity.getClass() == cls) { allEntities.add(entity); } } return allEntities; }

That works fine, but it means that when calling this method I still need to cast it to the class on the other side. For example:

asteroid = (Asteroid)PickEntities(Asteroid.class);

What I would like to do is use the class I am passing to my PickEntities class (the cls parameter) and then cast the returning array (allEntities) to that type.

Is there a way to do this? Whenever I try it just tells me that 'cls' is not a type and can't be used to cast.

Where is the class Array defined?

Antimony
– Antimony

2013-05-18 14:57:28 +00:00
Commented May 18, 2013 at 14:57 — Antimony
– Antimony, Commented May 18, 2013 at 14:57

JB Nizet · Accepted Answer · 2013-05-18 15:00:25Z

15

Your method should be generic:

public <T extends SpriteEntity> List<T> pickEntities(Class<T> clazz) { List<T> result = new ArrayList<T>(); for (SpriteEntity entity : MyGame.allEntities) { if (entity.getClass() == clazz) { result.add((T) entity); } } return result; }

Note that I used standard collection classes, and standard Java naming conventions.

answered May 18, 2013 at 15:00

JB Nizet

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3 Comments

boolean Over a year ago

Wow, that's some awesome code! Works perfectly, and I got a lesson in how to better use Java :D Thanks mate!

NamshubWriter Over a year ago

Note that the above code, like the code from the OP, will only include instances where the class is exactly the same as clazz; it won't include subclasses. Also, you can avoid the cast by calling clazz.cast(entity)

Vijayendra Vasu Over a year ago

If you want to include subclasses, you can use this code: if (clazz.isInstance(entity)) result.add(clazz.cast(entity));

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