Get Random Records in Apex

ramdomizer_script.cls

Integer sampleSize = 50;
//Testing functions by printing out names from sample db.
List<Contact> population = [SELECT LastName FROM Contact LIMIT 1000];
List<Contact> sample = getContactSample(population,sampleSize);
System.debug('sample size: ' + sample.size());
for(Contact sampledContact : sample){
    System.debug('Contact: ' + sampledContact.LastName);
}
public List<Contact> getContactSample(List<Contact> population, Integer sampleSize){
    List<Contact> sample = new List<Contact>();
    for(Integer i = 0; i < sampleSize; i++){
        //Get index of a random contact from the population.
        Integer indexOfContact = getRandomNumber(population.size() - sample.size());
        
        //Add contact to sample.
        sample.add(population[indexOfContact]);
        
        //Remove contact from population.
        population.remove(indexOfContact);
    }
    return sample;
}    
public Integer getRandomNumber(Integer ceiling){
    return Integer.valueof((Math.random() * ceiling));
}