You need to initialize local variables before they are used as below public void method() { Object o=null; try { o = new Object(); } catch (Exception e) { handleError(); } doSomething(o); } You will not get the compilation failure until you use local variable which was not initialized
The problem is that GenericTraversableTemplate is used twice: once for mutable collections (where its type parameter should be invariant), and once for immutable collections (where covariance is invariably king). GenericTraversableTemplate’s typechecks assuming either covariance or invariance for the A type parameter. However, when we inherit it in a mutable trait, we have to pick invariance. … Read more
Yes – this is a natural consequence of type erasure. If o is actually an instance of Action<String> that won’t be caught by the cast – you’ll only see the problem when you try to use it, passing in a ClientInterface instead of a string. You can get rid of the warning using: @SuppressWarnings(“unchecked”) as … Read more
getView() is called whenever a previously invisible list item needs to be drawn. Since you recreate itemChecked[] each time this method is called you will have the new checkbox unchecked and a different Array for each resulting View. (final in Java does not make that field unique like in C) Simplest way to solve that … Read more
To elaborate on what Peter wrote: Casts from non-generic types to generic types may work just fine at runtime, because the generic parameters are erased during compilation, so we are left with a legitimate cast. However, the code may fail later with an unexpected ClassCastException due to an incorrect assumption regarding the type parameter. For … Read more
From JLS 4.8 Raw Types The use of raw types is allowed only as a concession to compatibility of legacy code. The use of raw types in code written after the introduction of generics into the Java programming language is strongly discouraged. and The type of a constructor (§8.8), instance method (§8.4, §9.4), or non-static … Read more
The problem is that a cast is a runtime check – but due to type erasure, at runtime there’s actually no difference between a HashMap<String,String> and HashMap<Foo,Bar> for any other Foo and Bar. Use @SuppressWarnings(“unchecked”) and hold your nose. Oh, and campaign for reified generics in Java 🙂
Sometimes Java generics just doesn’t let you do what you want to, and you need to effectively tell the compiler that what you’re doing really will be legal at execution time. I usually find this a pain when I’m mocking a generic interface, but there are other examples too. It’s usually worth trying to work … Read more