Java Community | Help. Code. Learn.•10mo ago

how does open-closed principle really work?

hey guys. i have a question an id like to hear other opinions. lets say i have this.:

public class MyService{
  //class fields, getters, setters
  public myServiceMethod(Car car){
    if(car.getColor()=="Red"){
      Print("Red car");
    }
    if(car.getColor()=="Green"){
        Print("Green car");
      }
    //do other business logic
  }
}

public class MyService{
  //class fields, getters, setters
  public myServiceMethod(Car car){
    if(car.getColor()=="Red"){
      Print("Red car");
    }
    if(car.getColor()=="Green"){
        Print("Green car");
      }
    //do other business logic
  }
}

it works fine. but then there comes a point when i need to check if the car is Yellow and Blue. then it means i have to add more if statements:

public class MyService{
  //class fields, getters, setters
  public myServiceMethod(Car car){
    if(car.getColor()=="Red"){
      Print("Red car");
    }
    if(car.getColor()=="Green"){
        Print("Green car");
    }
    if(car.getColor()=="Yellow"){
        Print("Yellow car");
    }
    if(car.getColor()=="Blue"){
        Print("Blue car");
    }
    //do other business logic
  }
}

public class MyService{
  //class fields, getters, setters
  public myServiceMethod(Car car){
    if(car.getColor()=="Red"){
      Print("Red car");
    }
    if(car.getColor()=="Green"){
        Print("Green car");
    }
    if(car.getColor()=="Yellow"){
        Print("Yellow car");
    }
    if(car.getColor()=="Blue"){
        Print("Blue car");
    }
    //do other business logic
  }
}

now the questions arise: 1. is adding more if statements considered to be extension or modification? In my understanding its both. You modify code all the time. You changed variable name? Its modification. In Cambridge dictionary modification is described as a change to something. Refactoring is modification too. You cant write excellent code from the first try. 2. does the first and second pieces of code follow open-closed principle? why?

13 Replies

JavaBot•10mo ago

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dan1st•10mo ago

In that example, you have to modify an existing class so its a modification but the open closed principle would be about writing your code in a way that it can be extended if applicable also your code has a bug

JavaBot•10mo ago

Looks like you're having some trouble comparing strings, check out this stackoverflow question for help.

dan1st•10mo ago

and you might want to use an enum instead of Strings (then you can also use an exhaustive switch)

bambizas19OP•10mo ago

its just a pseudocode for the sake of example

ayylmao123xdd•10mo ago

i think the factory pattern for this would be better

dan1st•10mo ago

that's for constructing object and not applicable to this question

ayylmao123xdd•10mo ago

lol wrong pattern i meant the strategy one making a component for each color

dan1st•10mo ago

nah we don't need that What's the next suggestion? A visitor for all the colors? 😂 (Don't do that - use switch instead if you want that - which is also better than a strategy in most cases similar to the one described (or just create a method in the enum or whatever object you are using instead of colors if applicable lol))

tjoener•10mo ago

I told OP yesterday to read about the expression problem Which is why open-closed is a "sometimes"

ayylmao123xdd•10mo ago

https://tenor.com/view/cat-smiling-cat-grey-cat-cute-cat-gif-2949633679466643461

Tenor

ayylmao123xdd•10mo ago

its called overengineering new trend in programming

JavaBot•10mo ago

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how does open-closed principle really work?

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