Generics in HashMap implementation

Question

In the Java implementation, I found

 transient Entry[] table; 
 which is initiated in constructor as
 table = new Entry[capacity];

I know and u

Answer 1

Try to think of Java Generics this way: type parameters only apply to the static type of reference-typed expressions and do not apply to the type of actual instances being referred to by the reference values at runtime.

I find the above key to developing the proper intuitions when reading Java code. So the next time you see

new HashMap()

read it as follows: "This is an instance creation expression of the type HashMap. At runtime this expression will yield a reference to an instance of the HashMap class." As long as the compiler can precisely track what you do with the result of that expression, it can maintain the knowledge that this is indeed a HashMap, but no further than that.

Now, since the static type system is not powerful enough to track the type parameters on the component type of arrays (the fact that Java's array types are covariant plays strongly here), the code is forced to break out of the static type safety network. The key observation is that on its own, this does not make the code incorrect, it only constrains the power of the compiler to find programming mistakes. This is why Java allows you to make unchecked casts from raw into generic types, although not without a warning which marks the spot where you have left the provinces of static type safety.