generic-method

问题 If you create a generic class in Java (the class has generic type parameters), can you use generic methods (the method takes generic type parameters)? Consider the following example: public class MyClass { public <K> K doSomething(K k){ return k; } } public class MyGenericClass<T> { public <K> K doSomething(K k){ return k; } public <K> List<K> makeSingletonList(K k){ return Collections.singletonList(k); } } As you would expect with a generic method, I can call doSomething(K) on instances of

问题 Why does the following code compile? The method IElement.getX(String) returns an instance of the type IElement or of subclasses thereof. The code in the Main class invokes the getX(String) method. The compiler allows to store the return value to a variable of the type Integer (which obviously is not in the hierarchy of IElement ). public interface IElement extends CharSequence { <T extends IElement> T getX(String value); } public class Main { public void example(IElement element) { Integer x

问题 Here\'s a question, this first code listing compiles just fine (JDK 1.6 | JDK 1.7): ArrayList<String> a = new ArrayList<String>(); String[] s = a.toArray(new String[0]); However, if I declare the List reference as a raw type: ArrayList a = new ArrayList(); String[] s = a.toArray(new String[0]); I get a compiler error saying the String[] is required but Object[] was found. This means my compiler is interpreting the generic method as returning Object[] despite of receiving a String[] as its