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

Run the flowing code:

public class Test {
    ArrayList[] f0;
    ArrayList f1;
    ArrayList[] f2;
    public static void main(String[] args) {
        Test t = new Test();
        Field[] fs = t.getClass().getDeclaredFields();
        for(Field f: fs ){
            System.out.println(f.getType().getName());
        }

    }

}

You will get:

[Ljava.util.ArrayList;
java.util.ArrayList
[Ljava.util.ArrayList;

Because Java don't support generic array. When you declare：

private ArrayList[] x;

The compiler will think it is :

private ArrayList[] x;

So, you should do like that:

int n = 10;
ArrayList[] f = new ArrayList[n];
for(int i=0;i();
}