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

If an object's creation/existence dependents on another object which can't be tailored, its tight coupling. And, if the dependency can be tailored, its loose coupling. Consider an example in Java:

class Car {

    private Engine engine = new Engine( "X_COMPANY" ); // this car is being created with "X_COMPANY" engine
    // Other parts

    public Car() { 
        // implemenation 
    }

}

The client of Car class can create one with ONLY "X_COMPANY" engine.

Consider breaking this coupling with ability to change that:

class Car {

    private Engine engine;
    // Other members

    public Car( Engine engine ) { // this car can be created with any Engine type
        this.engine = engine;
    }

}

Now, a Car is not dependent on an engine of "X_COMPANY" as it can be created with types.

A Java specific note: using Java interfaces just for de-coupling sake is not a proper desing approach. In Java, an interface has a purpose - to act as a contract which intrisically provides de-coupling behavior/advantage.

Bill Rosmus's comment in accepted answer has a good explanation.