Java question about ArrayList[] x

Question

I have always had this one issue with arrays of ArrayLists. Maybe you can help.

//declare in class
private ArrayList[] x;

//in constructor
x=new          


        

Answer 1

It shouldn't have been an error. A warning is enough. If nobody can create an ArrayList[], there is really no point to allow the type.

Since javac doesn't do us the favor, we can create the array ourselves:

@SuppressWarnings("unchecked")
 E[] newArray(Class classE, int length)
{
    return (E[])java.lang.reflect.Array.newInstance(classE, length);
}

void test()
    ArrayList[] x;
    x = newArray(ArrayList.class, 10);

The type constraint isn't perfect, caller should make sure the exact class is passed in. The good news is if a wrong class is passed in, a runtime error occurs immediately when assigning the result to x, so it's fail fast.