The interface segregation principle is concerned with keeping interfaces highly cohesive, engaged in only one task or a set of tasks that are highly related. It states that no client should be forced to depend on methods that it does not use.
This principle is similar in spirit to the principle of single responsibility: its goal is to ensure that you create focused and highly-cohesive abstractions that are only concerned with a single area of responsibility. But instead of making you consider the concept of responsibility itself, it makes you look at the interfaces that you're creating and consider whether they're appropriately segregated.
Consider a local government office. They have a paper form (let's call ...
