Adapter notes

The problem

A matrix manipulation package provides operations such as addition and subtraction of matrices. These operations are static which introduce an interesting twist to the problem. For example, one cannot introduce an interface or abstract class to define matrices. Interfaces and abstract classes cannot define static methods. The class is like:

  public class Matrix {
      protected Matrix (Matrix m) {...}          // shallow copy
      public Matrix (double [] [] entry) {...}
      public static Matrix plus (Matrix l, Matrix r) {...}
      public static Matrix minus (Matrix l, Matrix r) {...}
  }

A client expects operations with a different identifier (name), e.g., add instead of plus.

      public static Matrix add (Matrix l, Matrix r) {...}
      public static Matrix sub (Matrix l, Matrix r) {...}

The twist

The matrix manipulation package is given and it should not be modified. The client should be modified as little as possible. Observe that the matrix operations are static. This makes sense. Adding two matrices together should not modify either addend.

Related patterns

- Delegation: when not to use inheritance
- Proxy: hide one object from another
- Adapter: keep one class independent of another
- Facade: single interface to several classes