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This PHP example shows interface implementations instead of subclassing (however, the same can be achieved through subclassing). The factory method can also be defined as public and called directly by the client code (in contrast to the previous Java example).
The client code deals only with the abstract type. Objects of a concrete type are indeed created by the factory, but the client code accesses such objects only through their abstract interface. Adding new concrete types is done by modifying the client code to use a different factory, a modification which is typically one line in one file.
By convention the only constructor is named new, though it is allowed to name it otherwise, or to have multiple constructors. For example, a Person class may have a constructor named new, and a constructor new_from_file which reads a file for Person attributes, and new_from_person which uses another Person object as a template.
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Java is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible. It is a general-purpose programming language intended to let programmers write once, run anywhere (), [16] meaning that compiled Java code can run on all platforms that support Java without the need to recompile. [17]
For example, the Java language does not allow client code that accesses the private data of a class to compile. [12] In the C++ language, private methods are visible, but not accessible in the interface; however, they may be made invisible by explicitly declaring fully abstract classes that represent the interfaces of the class.
Objects can contain other objects in their instance variables; this is known as object composition. For example, an object in the Employee class might contain (either directly or through a pointer) an object in the Address class, in addition to its own instance variables like "first_name" and "position".
This example uses a String as the state, which is an immutable object in Java. In real-life scenarios the state will almost always be a mutable object, in which case a copy of the state must be made. It must be said that the implementation shown has a drawback: it declares an internal class.