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Mock objects have the same interface as the real objects they mimic, allowing a client object to remain unaware of whether it is using a real object or a mock object. Many available mock object frameworks allow the programmer to specify which methods will be invoked on a mock object, in what order, what parameters will be passed to them, and what values will be returned.
Mock objects differ in that they themselves contain test assertions that can make the test fail, for example, if the person's name and other data are not as expected. Fake and mock object methods that return data, ostensibly from a data store or user, can help the test process by always returning the same, realistic data that tests can rely upon.
The factory method design pattern solves problems such as: How can an object's subclasses redefine its subsequent and distinct implementation? The pattern involves creation of a factory method within the superclass that defers the object's creation to a subclass's factory method.
However, the factory only returns a reference (in Java, for instance, by the new operator) or a pointer of an abstract type to the created concrete object. This insulates client code from object creation by having clients request that a factory object create an object of the desired abstract type and return an abstract pointer to the object. [5]
The facade pattern (also spelled façade) is a software design pattern commonly used in object-oriented programming.Analogous to a façade in architecture, it is an object that serves as a front-facing interface masking more complex underlying or structural code.
A fluent interface is normally implemented by using method chaining to implement method cascading (in languages that do not natively support cascading), concretely by having each method return the object to which it is attached [citation needed], often referred to as this or self.
In turn, this places restrictions on any abstraction that uses the singleton, such as preventing concurrent use of multiple instances. [ 8 ] [ 9 ] [ 10 ] Singletons also violate the single-responsibility principle because they are responsible for enforcing their own uniqueness along with performing their normal functions.
If it is initialized, return it immediately. Obtain the lock. Double-check whether the variable has already been initialized: if another thread acquired the lock first, it may have already done the initialization. If so, return the initialized variable. Otherwise, initialize and return the variable.