Java and mode Reading Note 5-interface isolation principle (ISP) and synthesis/aggregation Reuse Principle (CARP)

Interface isolation principle (ISP): it is better to use multiple special interfaces than to use a single total interface.

The dependence of a class on another class should be based on the smallest interface.

An interface represents a role, and different roles should not be assigned to an interface. Unrelated interfaces are merged to form a bloated large interface, which is a pollution to roles and interfaces.

 

Synthesis/aggregation Reuse Principle (CARP): Also known as the synthesis Reuse Principle (CRP), is to use some existing objects in a new object to make it a part of the new object; new objects reuse existing functions by assigning them. In short, we should try to use synthesis/aggregation instead of inheritance.

Aggregation: used to indicate the "owned" relationship or the relationship between the whole and the part.

Synthesis: used to indicate a much stronger "ownership" relationship. In a synthesis, the partial and overall life cycles are the same. A new object to be merged has full right to control its components, including their creation and elimination.

The multiple features of a synthesis cannot pass through one. The component objects in a synthesis relationship cannot be shared with another synthesis relationship. A component object can belong to only one compositing relationship.

Basic Types of multiplexing:

Merging/aggregation multiplexing:

Advantages:

* The only way for a new object to access a component object is through the component object interface.

* This reuse method is black box reuse, because the internal details of component objects are invisible to new objects.

* This type of reuse supports packaging.

* This reuse requires less dependencies.

* Each new class can focus on a task.

* This type of reuse can be performed dynamically during running time. New objects can dynamically reference objects of the same type as component objects.

Disadvantages:

* Many objects need to be managed in the system.

Reuse through inheritance:

Synthesis/aggregation can be applied to almost any environment as a means of reuse, but inheritance can only be used in a limited environment. Although inheritance is a very important method of reuse, synthesis/aggregation should be considered first, rather than inheritance.

Advantages:

* The new implementation is easier, because most of the functions of the superclass can automatically enter the subclass through the inherited relationship.

* It is easier to modify and extend the inherited implementations.

Disadvantages:

* Inheritance reuse destroys the packaging because inheritance exposes the implementation details of the superclass to the subclass. Because the internal details of superclasses are often transparent to sub-classes, this reuse is transparent, also known as "white box" reuse.

* If the superclass changes, the implementation of the subclass must also change.

* The implementation inherited from the superclass is static and cannot be changed during the running time, without sufficient flexibility.

 

When re-purchasing a design that violates the Li's replacement principle, there are two methods: one is to add an abstract superclass, and the other is to change inheritance to a synthetic/aggregate relationship.

"Is-A" indicates that one class Is another class. "Has-A" indicates that one class Is A role of another class, rather than A special class. Inheritance should be considered for "Is-A", while "Has-A" uses synthesis/aggregation.