"Program to an interface, not an implementation" is a famous quote by Gang of Four. Even if it is not the definition of the dependency inversion principle, it is really close to it. Another related quote is by Robert C. Martin: "depend on abstractions, not on concretions". While writing this blog post I concretely learned what these quotes practically mean.
Interface segregation principle (ISP) says that clients should not be forced to depend upon interfaces that they do not use. Practically that means that we should have rather small interfaces with just few (or even one) methods than fat interfaces with many methods. In this blog post I will explain what ISP is and what relationship it has with Liskov substitution and single responsibility principles.
You can't get any idea of what Liskov substitution principle (LSP) is from its name. And its definition is hard to understand. But when you dig into it you'll find that it is quite important and not that difficult principle. It has a relationship with open/closed principle and contract by design. LSP guarantees that every object of subclasses behaves just like superclass. In this blog post I will explain what LSP is and how it helps to make better code.