Callers

Small library that gives access to getCallerClass() for Java 8 (faster than instantiation of new Throwable)
API contains two methods:
getCallerClass() - returns caller class for function where getCallerClass() called from
getCallerClass(int index) - returns caller class for function that is index stackframes higher than the current function (for 1 it returns this class, 2 — same as getCallerClass(), 3 — caller of caller, etc)

Usage example:

package com.mycompany;

class MyVerySecretClass {
	private static final MyVerySecretClass instance = new MyVerySecretClass();
	private MyVerySecretClass() {}

	// ... some great functionality ...

	public static MyVerySecretClass getInstance() {
		if (!Callers.getCallerClass().getName().startsWith("com.mycompany"))
			throw new SecurityException("No MyVerySecretClass instances for your package!");
		return instance;
	}
}