java: How to fix the Unchecked cast warning

Question

I've got the following code:

private HashMap<Class<?>, HashMap<Entity, ? extends Component>> m_componentStores;  public <T extends Component> T getComponent(Entity e, Class<T> exampleClass) {     HashMap<Entity, ? extends Component> store = m_componentStores.get(exampleClass);      T result = (T)store.get(e);      if (result == null)     {         throw new IllegalArgumentException( "GET FAIL: "+e+" does not possess Component of class\nmissing: "+exampleClass );     }      return result; } 

When I compile, it shows that T result = (T)store.get(e) has an unchecked cast.

Type safety: Unchecked cast from capture#2-of ? extends Component to T 

What am I missing to prevent this warning from appearing?

Answer 1

Class.cast is what you want. Well, you might consider not using reflection.

Change the line:

T result = (T)store.get(e); 

to:

T result = exampleClass.cast(store.get(e)); 

Answer 2

Write @SuppressWarnings("unchecked") above the Cast statement:

@SuppressWarnings("unchecked") T result = (T)store.get(e); 

And add a explanatory statement why it is safe to ignore the warning.