Why do I have generic array creation error? [duplicate]

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class Generic<T> {}
Generic<Object> gib;
gib = new Generic<Object>[5]; // here is the line throwing Generic array creation error


I don't understand why this sample should be considered generic array creation, because the generic array creation I've seen so far is created in the form like Generic<T>[SIZE], with an unknown type parameter. But in this sample, I explicitly set the type parameter to Object, I guess my understanding of generic array must have some flaws, hope someone could help.

Generic<T>[SIZE]

Object

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Object arr = new String[2];

arr[1] = 1;

1

String

T

Object

List

List<Generic<Object>> list = new ArrayList<>();

T

Object

Object

1 Answer
1

You can't do this because at runtime, the generic type parameters will be erased and you'd lose type safety.

Here's a code snippet that demonstrates this, taken from here

Object stringLists = new List<String>; // compiler error, but pretend it's allowed
stringLists[0] = new ArrayList<String>(); // OK
stringLists[1] = new ArrayList<Integer>(); // An ArrayStoreException should be thrown,
// but the runtime can't detect it.


"The runtime can't detect it" because the type parameters are gone at runtime. The runtime thinks ArrayList<String> and ArrayList<Integer> are the same thing - ArrayList. It doesn't matter what generic type parameter you put when you create the array.

ArrayList<String>

ArrayList<Integer>

ArrayList