Mixing COP and OOP

We describe and justify thirteen technical properties that a component system must possess to work with object-oriented programming languages (such as Java, C++, or C#). Our components are designed for large-scale, modular construction of programs with static checking of program compositions. Jiazzi, our enhancement of Java, implements the technical properties that we describe. We use Jiazzi components in our examples, but only to make the discussion more concrete. Readers interested in the details of the Jiazzi component system should refer to our technical paper in OOPSLA '01 [8]. P1. Language support: Components should be described with a specific language construct. P2. Core language integration: Components should contain, import and export instances of constructs in the core language. As object-oriented software systems increase in size and complexity , components are becoming central to the design process, and they deserve language support. Otherwise, the lack of an explicit language construct for components places a substantial burden on programmers who implement components, and it obscures the pro-grammer's intent to the compiler and other programmers. Furthermore, components should be integrated with the core language , as opposed to working around the language with various compositional design patterns [6]. In class-based languages, the primary core language construct is the class, and large-scale elements of reuse are class libraries and frameworks. Jiazzi's units [5] are explicit language constructs that describe components. There are two types of units: atoms, which are built from Java classes, and compounds, which are built from other units. Both atoms and compounds import and export Java classes. P3. Coarse-grained connections: Connections between imports and exports should be able to connect many classes at once. Connections between components should be coarse-grained, because components represent large-scale software entities. Components should import, export, and connect together groups of classes, since management of individual imported and exported classes does not scale with larger designs. In Jiazzi, groups of classes are imported together, exported together, and connected together when units are linked; we call these groups of classes packages to emphasize their similarity to packages in standard Java. P4. Hierarchical composition: A component should be com-posable into a larger, encapsulated component. P5. Component instantiation: A component should be instantiated for each use. P6. External linking: A component's external class dependencies should be resolved by the user of the component. Composition of components to form larger, compound components enables the incremental construction of software. Outside a compound component, …