What is the difference between loose coupling and tight coupling in the object oriented paradigm?

Question

Can any one describe the exact difference between loose coupling and tight coupling in Object oriented paradigm?

Answer 1

Tight coupling means classes and objects are dependent on one another. In general, tight coupling is usually not good because it reduces the flexibility and re-usability of the code while Loose coupling means reducing the dependencies of a class that uses the different class directly.

Tight Coupling The tightly coupled object is an object that needs to know about other objects and is usually highly dependent on each other's interfaces. Changing one object in a tightly coupled application often requires changes to a number of other objects. In the small applications, we can easily identify the changes and there is less chance to miss anything. But in large applications, these inter-dependencies are not always known by every programmer and there is a chance of overlooking changes. Example:

    class A {
       public int a = 0;
       public int getA() {
          System.out.println("getA() method");
          return a;
       }
       public void setA(int aa) {
          if(!(aa > 10))
             a = aa;
       }
    }
    public class B {
       public static void main(String[] args) {
          A aObject = new A();
          aObject.a = 100; // Not suppose to happen as defined by class A, this causes tight coupling.
          System.out.println("aObject.a value is: " + aObject.a);
       }
    }

In the above example, the code that is defined by this kind of implementation uses tight coupling and is very bad since class B knows about the detail of class A, if class A changes the variable 'a' to private then class B breaks, also class A's implementation states that variable 'a' should not be more than 10 but as we can see there is no way to enforce such a rule as we can go directly to the variable and change its state to whatever value we decide.

    Output
    aObject.a value is: 100

Loose Coupling
Loose coupling is a design goal to reduce the inter-dependencies between components of a system with the goal of reducing the risk that changes in one component will require changes in any other component.
Loose coupling is a much more generic concept intended to increase the flexibility of the system, make it more maintainable and makes the entire framework more stable.
Example:

class A {
   private int a = 0;
   public int getA() {
      System.out.println("getA() method");
      return a;
   }
   public void setA(int aa) {
      if(!(aa > 10))
         a = aa;
   }
}
public class B {
   public static void main(String[] args) {
      A aObject = new A();
      aObject.setA(100); // No way to set 'a' to such value as this method call will
                         // fail due to its enforced rule.
      System.out.println("aObject value is: " + aObject.getA());
   }
}

In the above example, the code that is defined by this kind of implementation uses loose coupling and is recommended since class B has to go through class A to get its state where rules are enforced. If class A is changed internally, class B will not break as it uses only class A as a way of communication.

Output
getA() method
aObject value is: 0