error: expected when making array of generics

Question

I am trying to create an array of generics by type casting, but everything I've tried has resulted in error: <identifier> expected. The task is to make an array based Deque. I've tried:

@suppresswarning("unchecked")
Random rewriting of the code

Here is a snippet of the code

public class dequeCyclic<E> implements Deque<E> {
private int first;
private int last; 
private E[] deque;

public dequeCyclic(int size){
    @SuppressWarning("unchecked")
    deque =(E[]) new Object[size];
    first = -1; 
    last = -1; 
}

Any help would be greatly appreciated.

Do you really need a type casting? Type casting is kind of bad design — Stepan Shcherbakov, Mar 26 '21 at 09:14
@StepanShcherbakov that's not possible, Java doesn't allow creation of generic arrays. — Thomas, Mar 26 '21 at 09:21
@macas523 does this answer your question: https://stackoverflow.com/questions/529085/how-to-create-a-generic-array-in-java ? — Stepan Shcherbakov, Mar 26 '21 at 09:24
As far as I know `@SuppressWarnings` isn't allowed on statements so it's on the wrong place here. (It would be allowed on local variable declarations but your statement isn't one.) `deque =(E[]) new Object[size];` should compile so if you still get a compiler error there might be a problem elsewhere in your code which confuses the compiler. One thing to note: stick to the coding conventions, e.g. class names start with a capital letter (`DequeCyclic`). This will help reduce confusion. — Thomas, Mar 26 '21 at 09:26
@StepanShcherbakov I did a variation of it and it worked, thank you — macas523, Mar 26 '21 at 09:28

score 0 · Answer 1 · answered Mar 26 '21 at 09:27

You can't put @SuppressWarning on statements. They are only allowed on declarations, so you have three options, either annotate the class:

@SuppressWarning("unchecked")
public class dequeCyclic<E> implements Deque<E> {

or the constructor:

@SuppressWarning("unchecked")
public dequeCyclic(int size) {
    deque =(E[]) new Object[size];
    first = -1; 
    last = -1; 
}

Or create a local temporary variable:

public dequeCyclic(int size) {
    @SuppressWarning("unchecked")
    E[] temp =(E[]) new Object[size];
    deque = temp;
    first = -1; 
    last = -1; 
}

The last one with the temporary variable should be prefered, because the first and second variant suppress all unchecked warnings inside of them. Which is generally more harmful than useful.

error: expected when making array of generics

1 Answers1