Retrieving a Random Item from Arraylist

Retrieving a random item from ArrayList

anyItem is a method and the System.out.println call is after your return statement so that won't compile anyway since it is unreachable.

Might want to re-write it like:

import java.util.ArrayList;
import java.util.Random;

public class Catalogue
{
    private Random randomGenerator;
    private ArrayList<Item> catalogue;

    public Catalogue()
    { 
        catalogue = new ArrayList<Item>();
        randomGenerator = new Random();
    }

    public Item anyItem()
    {
        int index = randomGenerator.nextInt(catalogue.size());
        Item item = catalogue.get(index);
        System.out.println("Managers choice this week" + item + "our recommendation to you");
        return item;
    }
}

How to pick a random item from a arraylist in java?

Simple, put your code in a method like this

Random rand; // Global variable

public static int randomItem(Arraylist<Integer> mylist) {
    rand = new Random(); 
    Integer randomInt = lista.get(rand.nextInt(lista.size()));
    return randomInt;
}

and call it like this in your main method;

int selected = randomItem(mylist);
System.out.println(selected);

Select Random element from ArrayList print then remove It

Fast and simple, make use of Collections.shuffle

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        list.add("a");
        list.add("b");
        list.add("c");
        list.add("d");
        list.add("e");

        while (!list.isEmpty()) {
            // You don't need to do this on each iteration
            // but this is going to give you a really
            // random result
            Collections.shuffle(list);
            String value = list.remove(0);
            System.out.println(value);
        }
    }
}

First run...

e
a
c
d
b

Second run...

a
e
d
b
c

Obviously, each run will give different results

Take n random elements from a ListE?

Two main ways.

1. Use Random#nextInt(int):

   List<Foo> list = createItSomehow();
   Random random = new Random();
   Foo foo = list.get(random.nextInt(list.size()));
   

   It's however not guaranteed that successive n calls returns unique elements.

2. Use Collections#shuffle():

   List<Foo> list = createItSomehow();
   Collections.shuffle(list);
   Foo foo = list.get(0);
   

   It enables you to get n unique elements by an incremented index (assuming that the list itself contains unique elements).

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In case you're wondering if there's a Java 8 Stream approach; no, there isn't a built-in one. There's no such thing as Comparator#randomOrder() in standard API (yet?). You could try something like below while still satisfying the strict Comparator contract (although the distribution is pretty terrible):

List<Foo> list = createItSomehow();
int random = new Random().nextInt();
Foo foo = list.stream().sorted(Comparator.comparingInt(o -> System.identityHashCode(o) ^ random)).findFirst().get();

Better use Collections#shuffle() instead.

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