java.lang.ArrayIndexOutOfBoundsException - error in code Java

So I have this problem... I wanna make a program where the user inputs a num numbers and then decide if he wants to sort them or search for a number... I get the Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0 at es_personali.es_ordinamenti.main(es_ordinamenti.java:33) error.

Can someone help me? Heres the code

    package es_personali;

    import java.util.*;
    public class es_ordinamenti {

static Scanner in = new Scanner(System.in);
static int num;
static int[] arr =new int[num];
public static void menu(){
    System.out.println("|              Cosa vuoi fare?");
    System.out.println("|");
    System.out.println("| 1 - Inserire numeri");
    System.out.println("| 2 - Ordinare in ordine crescente");
    System.out.println("| 3 - Ricercare un numero");
    System.out.println("| 0 - Uscire");
}
public static void main(String[] args){

    int ris;
    boolean inseriti=false;

    System.out.println("------------------BENVENUTO!------------------");
    menu();
    do{
        System.out.println(">>");
        ris = in.nextInt();
        if(ris==1){
                System.out.println("Quanti numeri?");
                num = in.nextInt();
                for (int i = 0; i < num ; i++) {
                    System.out.print(">>");
                    arr[i]=in.nextInt();
                }
            inseriti=true;
        }else if(ris==2){
            if(inseriti){
                    System.out.println("Stampa senza ordinamento: ");
                    for (int i = 0; i < num; i++) {
                        System.out.println(arr[i]);
                    }
                    System.out.println("Stampa con ordinamento: ");
                    Arrays.sort(arr);
                    for (int i = 0; i < num; i++) {
                        System.out.println(arr[i]);
                    }

            }else System.out.println("Non hai inserito i numeri.");
        }
        else if(ris==3){
                    System.out.println("Inserire numero da ricercare: ");
                    int ricerca = in.nextInt();
                    System.out.println("Numero " + ricerca + " trovato nell'indice: " + Arrays.binarySearch(arr, ricerca));

            }
    }while(ris!=0);


}

}

The code is currently incomplete, but if you can't understand something let me know!

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