SOLID PRINCIPLES: Open Closed

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SOLID PRINCIPLES: Open Closed

· java

SOLID principles basically form the fundamental guidelines for building 

👉 object-oriented , 

👉 loosely coupled , 

👉 robust, maintainable and 

👉 easily understandable applications .

A class should be open for extension but closed for modification 

which essentially means we do not want our existing code to be modified causing potential issues or bugs .

Other developers in case of some functionality change should be able to extend our class and override some methods.

For ex:

public class VehiclePrice {
  public double Value(Vehicle v) {
    if (v instanceof Car) {
      return v.getValue() * 0.5;
      if (v instanceof Truck) {
        return v.getValue() * 0.8;
      }
    }
  }
}

If we want to add one more type to this ,say e-bike, 

we would have to modify the above class with one more if statement which goes against the principle.

A better way is to let the sub classes override the Value method as per their type.