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Cohesion

Degree to which members of a class serve a unifying task or concept

Abstractions and design should allow related methods and fields to be together

High cohesion is when 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.

Different types of Cohesion:

Better -> Worst

  • Functional Cohesion:
    • All code contributes to a single feature or task
  • Sequential Cohesion
    • Output from one step is input of the next step
    • This kind of cohesion is normal because these are the kinds of methods that allow the systems to perform complex tasks.
active(from: Mario) {
    // ..
    this.bounce();
    let coin = this.items.pop();
    coin.activate(from);
    this.actors.push(coin);
    // ..
}
  • Communicational Cohesion
    • Tasks grouped in method only because of the data
getRecord(key: string) {
    // ..
    if (key === 'bar') {
        this.translateBar(this.data)
    }
    if (key === 'baz') {
        this.translateBaz(this.data)
    }
    // ..
}

===> The first three kinds of cohesion indicate good program designs

  • Procedural Cohesion
    • Parts of a module are grouped because they always follow a certain sequence of execution
victory() {
    this.level.playMusic('win')
    this.clearFrames()
    this.view.show()
    this.setImage()
    this.level.next()
}
  • Temporal Cohesion
    • Functionality grouped because it happens at the same point in the execution of the system and isn't related at all.
    • Problematic
  • Logical Cohesion
    • Functionaliy combined for task, regardless of intent.
    • Functions do not make sense in their context
setLifes(lifes: number) {
    this.lifes = lifes
    this.level
        .word.parent()
        .children('#liveNumber')
        .text(this.lifes)
}
  • Coincidental Cohesion
    • Functionality arbitrarily grouped together
    • Hard to understand and reuse
    • Lack of any cohesion at all

More about cohesion:

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