Utility methods for the Java programming language.

Utilities.java

package com.amirkhawaja;

import java.security.SecureRandom;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Utilities() {
    
    private static final SecureRandom random;

    static {
        random = new SecureRandom();
    }
    
    /**
     * Private constructor.
     */
    private Utilities() {
    }
    
    /**
     * Create a new Thread Pool that will not chew max out CPU utilization.
     *
     * @return New thread pool.
     */
    public static ExecutorService newThreadPool() {
        final int processors = Runtime.getRuntime().availableProcessors();
        final int utilization = 1;
        final int waitComputeRatio = 50;

        // Number of threads: Number of CPU * CPU utilization * (1 + W/C)
        final int nThreads = processors * utilization * (1 + waitComputeRatio);

        return Executors.newFixedThreadPool(nThreads, runnable -> {
            final Thread thread = new Thread(runnable);
            thread.setDaemon(true);
            return thread;
        });
    }
    
    /**
     * Generate a random alphanumeric string.
     *
     * @return Random alphanumeric string.
     */
    public static String randomAlphanumeric(int length) {
        if (length == 0) {
            return "";
        } else if (length < 0) {
            throw new IllegalArgumentException("Length must be greater than zero");
        }

        final StringBuilder buffer = new StringBuilder(length);
        char ch;
        final int start = ' ';
        final int end = 'z' + 1;
        final int gap = end - start;

        while (length-- != 0) {
            ch = (char) (random.nextInt(gap) + start);
            if (Character.isLetterOrDigit(ch)) {
                buffer.append(ch);
            } else {
                length++;
            }
        }
        return buffer.toString();
    }
    
}