Tutorials : Inversion of Control: A Mechanism for Highly Flexible Applications :

Inversion of Control: A Mechanism for Highly Flexible Applications

by Samudra Gupta

Loose coupling is one of the critical elements in object-oriented software development. It allows you to change the implementations of two related objects without affecting the other object. Suppose you've got a situation in which making a change to the implementation details in component A forces you to make a change in component B (which uses component A). This is what is called a strong coupling, and it can make life more difficult when it comes to the scalability of an application. Inversion of Control (IoC) is one approach you can use to achieve loose coupling between several interacting components in an application.

What is IoC?

Class A {
  private B b;
  
  public A() {
       b = new B();
  }

  public void doSomething(){
    
      b.someMethod();
  }

1. The creation of object B relies upon the availability of a default constructor.
2. Any change in the constructor implementation of class B will necessitate achange in the implementation of class A.
3. Suppose class A wants to use class C instead of class B. Then class A needs to change. What happens if class B and class C are two separate implementations of same service and the application will need to switch over from one implementation to the other?

The solution to this problem is to eliminate the dependency from class A. What follows is a modified class A, where strong coupling is removed:

Class A {
  private B b;
  
  public A(B b) {
       this.b = b;
  }

  public void doSomething(){
    
      b.someMethod();
  }

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