Inversion of Control (IoC) means to create instances of dependencies first and latter instance of a class (optionally injecting them through constructor), instead of creating an instance of the class first and then the class instance creating instances of dependencies. Thus, inversion of control inverts the flow of control of the program. Instead of the callee controlling the flow of control (while creating dependencies), the caller controls the flow of control of the program.

​~https://stackoverflow.com/questions/3058/what-is-inversion-of-control

IoC is a programming technique, expressed here in terms of object-oriented programming, in which object coupling is bound at run time by an assembler object and is typically not known at compile time using static analysis.

​~http://en.wikipedia.org/wiki/Inversion_of_control

IoC is a common pattern in the Java community that helps wire lightweight containers or assemble components from different projects into a cohesive application.
~http://www.martinfowler.com/articles/injection.html (reworded)

Spring helps in the creation of loosely coupled applications because of Dependency Injection. 

​In Spring, objects define their associations (dependencies) and do not worry about how they will get those dependencies. It is the responsibility of Spring to provide the required dependencies for creating objects.

-https://stackoverflow.com/questions/9403155/what-is-dependency-injection-and-inversion-of-control-in-spring-framework

​public class MyRunnable implements Runnable{
  // this method is called when a runnable thread starts
  public void run(){
    printMessage();
  }
}

public class ThreadDemo{
  public static void main(String args[]){
    Thread t1 = new Thread(new MyRunnable); 
    Thread t2 = new Thread(new MyRunnable);
    Thread t3 = new Thread(new MyRunnable);
    t1.start();    
    t2.start();
    t3.start();
  }

  public static void printMessage(){
    System.out.println("Hello");
  }
}