solid-principles

问题 I have 3 classes, Account , CappedAccount , UserAccount , CappedAccount , and UserAccount both extend Account . Account contains the following: abstract class Account { ... /** * Attempts to add money to account. */ public void add(double amount) { balance += amount; } } CappedAccount overrides this behavior: public class CappedAccount extends Account { ... @Override public void add(double amount) { if (balance + amount > cap) { // New Precondition return; } balance += amount; } } UserAccount

问题 Just a thought and a question to the Stack Overflow and Microsoft Development Community about the OO software design principles called SOLID. What is the difference between the Liskov Substitution Principle and the Dependency Inversion Principle please ? I have thought about this for a while and I'm not sure of the difference. Please could you let me know ? Any thoughts / feedback very welcome. 回答1: Liskov's substitution Principle states the following: A class should be directly substitutable

问题 From Wikipedia, Liskov's notion of a behavioral subtype defines a notion of substitutability for objects; that is, if S is a subtype of T, then objects of type T in a program may be replaced with objects of type S without altering any of the desirable properties of that program (e.g. correctness). Suppose the following class hierarchy: The base abstract class - AnimalWithFur . It has a read-only property furColor that is overridden in successors. Base class's successor - Cat , which overrides

问题 Assume I have three classes like so. abstract class A { abstract protected function doSomething($object): array; } class B extends A { protected function doSomething(SomeObject $object): array { // something } } class C extends A { protected function doSomething(OtherObject $object): array { // something } } According to principles of inheritance as PHP does it, the structure described above is not legal PHP code, as the method definitions are not compatible with the base class. I can, of

问题 As per the Interface Segregation Principle clients should not be forced to implement the unwanted methods of an interface ...and so we should define interfaces to have logical separation. But default methods introduced in Java 8 have provided the flexibility to implement methods in Java interfaces. It seems Java 8 has provided the feasibility to enhance an interface to have some methods not related to its core logic, but with some default or empty implementation. Does it not violate the ISP?

问题 As per the Interface Segregation Principle clients should not be forced to implement the unwanted methods of an interface ...and so we should define interfaces to have logical separation. But default methods introduced in Java 8 have provided the flexibility to implement methods in Java interfaces. It seems Java 8 has provided the feasibility to enhance an interface to have some methods not related to its core logic, but with some default or empty implementation. Does it not violate the ISP?

问题 How does the SOLID "Interface Segregation Principle" differ from "Single Responsibility Principle"? The Wikipedia entry for SOLID says that ISP splits interfaces which are very large into smaller and more specific ones so that clients will only have to know about the methods that are of interest to them However, to me that sounds like just applying the SRP to interfaces as well as classes. After all, if an interface is only responsible for just one conceptual thing, than you wouldn't be able

问题 The Situation: I have three classes: Society, Father and Son. The Society has a list of Fathers. Each Father has one son. It is necessary in this application that each Father knows who his Son is and vice-versa each Son knows who his Father is. I have used direct cross referencing by assigning the Father as a property of the Son, and the Son as a property of the Father class, as below: public class Society : ISociety { public List<IFather> Fathers {get; set;} } public class Father : IFather {

问题 Could anyone tell me why does singleton break open/closed principle? Is it because there could be problems with inheriting from that class? 回答1: For a class to be "open" it must be possible to inherit from it. Inheritance is an "is-a" relationship. If you inherit from a singleton-class then instances of the child-class are also instances of the parent class due to the "is-a" relationship, meaning you can suddenly have multiple instances of the singleton class. If the singleton class inhibits

问题 Could anyone tell me why does singleton break open/closed principle? Is it because there could be problems with inheriting from that class? 回答1: For a class to be "open" it must be possible to inherit from it. Inheritance is an "is-a" relationship. If you inherit from a singleton-class then instances of the child-class are also instances of the parent class due to the "is-a" relationship, meaning you can suddenly have multiple instances of the singleton class. If the singleton class inhibits