CODEWITHSUNDEEP
liskov-substitution-principle
Roma Kap
Roma Kap

Reputation: 636

LSP - Liskov Substitution Principle particular case

i'am not sure about special case of LSP. Actually child should extend implementation of parent and not change it. For me means extension, that i add new lines in child implementation to parent implementation within child class. But what about, when i completely override parent-implementation and it provides result too?

Parent is:

public class Calculator {
     public void computeProfit(){
        int profit = 2+2;
     }
}

Child is:

public class SpecialCalculator  extends Calculator {
    @Override
    public void computeProfit(){
        //overriding completely parent-implementation
        int profit = Math.pow(2) * 5;
    }
}

has LSP still been preserved?

Upvotes: 0

Views: 103

Answers (1)

Bohdan Stupak
Bohdan Stupak

Reputation: 1593

TL;DR; In you example LSP is preserved. IMO the thing with SOLID principles it that it is a mnemonic for dynamic polymorphism so the end goal for your code is to enable something like this

public void SomeBusinessLogic(Calculator calc) {
  calc.computeProfit() // SpecialCalculator might go here as well
}

Your code is perfectly fit for this.

This however would violate LSP

public class SpecialCalculator  extends Calculator {
    public void computeProfitClevrly(){
        //overriding completely parent-implementation
        int profit = Math.pow(2) * 5;
    }
}

because now you'll have to do something like

public void SomeBusinessLogic(Calculator calc) {
  if (calc is SpecialCalculator)
     calc.computeProfitCleverly() // SpecialCalculator might go here as well
}

P.S. There are some more subtle cases of LSP violation. I.e. when base class is ImmutablePoint and a child class is a point that might be mutated.

Upvotes: 1

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