Cohesion in Java

Difficulty Level : Basic
Last Updated : 31 Oct, 2017

In object oriented design, cohesion refers all about how a single class is designed. Cohesion is the Object Oriented principle most closely associated with making sure that a class is designed with a single, well-focused purpose.
The more focused a class is, the cohesiveness of that class is more. The advantages of high cohesion is that such classes are much easier to maintain (and less frequently changed) than classes with low cohesion. Another benefit of high cohesion is that classes with a well-focused purpose tend to be more reusable than other classes.

Example : Suppose we have a class that multiply two numbers, but the same class creates a pop up window displaying the result. This is the example of low cohesive class because the window and the multiplication operation don’t have much in common.
To make it high cohesive, we would have to create a class Display and a class Multiply. The Display will call Multiply’s method to get the result and display it. This way to develop a high cohesive solution.

Lets understand the structure of high cohesive program :

// Java program to illustrate 
// high cohesive behavior 
class Multiply { 
    int a = 5; 
    int b = 5; 
    public int mul(int a, int b) 
    { 
        this.a = a; 
        this.b = b; 
        return a * b; 
    } 
}  
  
class Display { 
    public static void main(String[] args) 
    { 
        Multiply m = new Multiply(); 
        System.out.println(m.mul(5, 5)); 
    } 
} 

Output:

// Java program to illustrate 
// high cohesive behavior 
class Name { 
    String name; 
    public String getName(String name) 
    { 
        this.name = name; 
        return name; 
    } 
}  
  
class Age { 
    int age; 
    public int getAge(int age) 
    { 
        this.age = age; 
        return age; 
    } 
}  
  
class Number { 
    int mobileno; 
    public int getNumber(int mobileno) 
    { 
        this.mobileno = mobileno; 
        return mobileno; 
    } 
}  
  
class Display { 
    public static void main(String[] args) 
    { 
        Name n = new Name(); 
        System.out.println(n.getName("Geeksforgeeks")); 
        Age a = new Age(); 
        System.out.println(a.getAge(10)); 
        Number no = new Number(); 
        System.out.println(no.getNumber(1234567891)); 
    } 
} 

Output:

Geeksforgeeks
10
1234567891

Pictorial view of high cohesion and low cohesion:
Cohesion in Java
Explanation : In the above image, we can see that in low cohesion only one class is responsible to execute lots of job which are not in common which reduces the chance of re-usability and maintenance. But in high cohesion there is a separate class for all the jobs to execute a specific job, which result better usability and maintenance.

Difference between high cohesion and low cohesion:

High cohesion is when you have a class that does a well defined job. Low cohesion is when a class does a lot of jobs that don’t have much in common.
High cohesion gives us better maintaining facility and Low cohesion results in monolithic classes that are difficult to maintain, understand and reduces re-usability

This article is contributed by Bishal Kumar Dubey. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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