package net.dimensions;

public class Dimensions
{
    public static void init()
    {
        System.out.println("Initializing Dimensions...");
    }
}
package net.dimensions;

import java.util.Random;

public class Dimensions {

    private static Random rand;

    public static void init() {
        System.out.println("Initializing Dimensions...");
        rand = new Random();
    }

    public static Random getRandom(){
        return rand;
    }
}

Add Random instance into main class
Add Random instance into main class

So each plugin that uses a Random doesn't have to create it's own instance, but they are free to if they want to make one with a custom seed.