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+# Topic 1
+
+## Four OOP principles
+
+Abstraction
+:   Objects can hide implementation details, as with interfaces.
+
+Encapsulation
+:   Hide internal information from outside, like with getters and setters.
+
+Inheritance
+:   Classes can extend other classes, inheriting their methods.
+
+Polymorphism
+:   Speficying interfaces which multiple classes can implement.
+
+# Topic 2
+
+## Class composition
+
+```
+A <filled>- B
+```
+
+B er en del af A, og B vil ikke kunne fungere alene.
+A ejer B.
+
+## Class aggregation
+
+```
+A <>- B
+```
+
+A har B, men B kan også stå alene.
+A bruger B
+
+## Association
+
+```
+A --> B
+```
+
+A does something with B.
+
+
+## Exception vs Error
+
+Errors are unrecoverable.
+
+# Topic 3
+
+ 1. Use cases
+    Shows interfaction between things.
+ 2. Domain model
+ 3. Interaction diagrams
+    Shows more detailed interactions as a sequence diagram.
+ 4. Design class diagrams
+
+ This repeats multiple times as the requirements may change under development.
+ This is because unanticipated things might occur.
+
+## Use case
+
+These are pretty much as always, but here are some important words.
+
+Actor
+:   Who performs operations; a person, organization or computer system.
+
+Scenario
+:   What are the required interactions required.
+
+Alternate scenario
+:   What happens if something goes wrong. What can go wrong.
+
+## Requirements
+
+These diagrams are used to get the following requirements.
+
+- Functionality: what should the system do?
+- Usability: what kind of UI is needed?
+- Performance
+- Implementation constraints
+
+Domain rules
+:   Additional external constraints such as laws etc.
+
+
+## Domain model
+
+Not a part of design but analysis.
+
+Uses conceptual classes, which are real things not functions or data.
+
+Uses vocabulary of the current domain.
+
+Has associations like, class diagram and are interactions between these real objects.
+Examples:
+
+ -  A is part of B, or is contained in B
+ -  A is a description of B
+ -  A is used by B
+ -  A is owned by B
+ -  A is owned by B
+ -  A is an event affecting B
+
+Only include important association, as this is not a specification.
+
+Can include class attributes, but should not contain complex information.
+So a Flight maybe has a destination.
+
+
+# Topic 5
+
+## GUI
+
+Are:
+
+- Asynchronous
+- Components are in containers which are in a layout.
+
+# Topic 8 Interaction and Classes
+
+Creating a design from analysis.
+
+## Mapping objects
+
+Object can be mapped from the interaction design, borrowing names as much as possible.
+
+Objects can have to main responsibilities:
+
+ -  Doing things
+    Often methods, ex: Cashier has `scanItem()`.
+ -  Knowing things
+
+## Patterns
+
+Patterns are solution which fit multiple problems, such as having a `Listener`.
+
+### Grasp patterns
+
+General Responsibility Assignment Software Patterns.
+
+Main patterns:
+
+ -  Information expert:
+    Assign a task to the class which has the most information about it.
+ -  Creator:
+    B should create an object if it contains, records, uses, or has information about object.
+ -  Low coupling:
+    Uses encapsulation to define simple interfaces between classes, and passing data using standard formats.
+ -  High cohesion:
+    Create focused objects, instead of `god` objects. This can be done by keeping responsabilities related.
+ -  Controller:
+    Handles system input events, to seperate the interface from the main system.
+
+Coupling and cohesion manage class complexity.
+Strike a balance between object size and complexity.
+
+### Visibility
+
+Who can see what.
+Should avoid global visibility as much as possible.
+Achieved using *information hiding*.
+
+
+# Topic 9 Design Patterns
+
+Common language between developers.
+
+Always code using interfaces and not classes, always accept interfaces.
+
+Prefer object composition instead of inheritance (why use OOP then).
+
+Patterns can be used when designing, following types:
+
+ -  Creational: Creates new objects, hiding the creation process
+ -  Structural: Patterns concerning class composition
+ -  Behavioral: Communication between classes
+ -  Anti-patterns: Design features known to create problems
+
+## Factories
+
+Create objects without exposing creation logic.
+
+Eases polymorphism is the factory decides which type to create, and then cast to interface when returning.
+
+## Singleton
+
+An object which is only created once.
+Useful when dealing with drivers or sockets.
+
+1. Object A requests singleton C
+2. C is creates as it does not exist, and is returned to A
+3. B requests C
+4. Existing C is returned to B
+
+Special care must be taken when doing multithreading, and testing is also harder.
+
+## Builder
+
+Construct object in the same way as factories.
+Implements a `Builder` interface which is run then the product is needed.
+
+One can then build objects without worrying about complex constructor parameters.
+
+## Adapter
+
+Bridge between two incompatible interfaces.
+
+Should be kept as a minimum as deep layering can complicate design.
+
+## Filter pattern
+
+Implements searching.
+
+## Composite
+
+Contains other instances of the same type.
+Useful for creating trees.
+
+## Observer pattern
+
+Listens for events and notifies client.
+Often used in gui's.
+
+## Publish subscribe 
+
+Publishers publish messages, and subscribers can subscribe on specific events.
+This is orchestrated by a central broker.
+
+## Some anti patterns
+
+ -  *God object* with too many responsibilities
+ -  Sequential coupling: methods that must be called in order
+ -  Object orgy: unrestricted access to internal variables
+ -  Yo-yo problem: too many layers of inheritance
+ -  Spaghetti code: too many ad-hoc fixes
+ -  Error hiding
+ -  Object cesspool: reusing objects with unpredictable state
+
+# Topic 10
+
+What happens after first iteration, so first system has been developed.
+
+Clients may want more features.
+Here a good domain model can help, as it will facilitate new features easily.
+
+Interfaces can often help implement new features, as only the implementation must be replaced.
+
+## Maintanance
+
+The implementation after a changed design model.
+
+Much easier with a low coupling.
+
+Should be done on a production branch.
+
+# Topic 11
+
+Talking to databases in java happens with the JDBC api.
+
+## ACID
+
+ -  Atomicity
+ -  Consistency
+ -  Isolation
+ -  Durability
+
+## Testing
+
+Static testing
+:   Reviewing code.
+
+Dynamic testing
+:   Unit test, integration test and acceptance test.
+
+### Code review
+
+Single or as a team.
+Walk through the code, and become familiar with code.
+
+Often af good way to ensure correct documentation and code style.
+
+### White box testing
+
+Testing with knowledge of implementation.
+
+Path testing
+:   Does the program reach the correct statements
+
+Data flow testing
+:   Do variables have expected values at times
+
+Fault injection
+:   How do methods handle invalid input
+
+Condition/decision testing
+:   Have all possible outcomes been tested using above
+
+#### Intergration testing
+
+Test modules together, are there any problems.
+
+Bottom-up
+:   Start with classes, then modules and end at a full program
+
+Top-down
+:   Start from main method, and gradually add components
+
+### Black box
+
+Should not use knowledge of the implementation.
+
+#### Acceptance testing
+
+Test the different use-cases, from the perspektive of the user.
+
+Often done by external testers.
+
+#### Automated unit test
+
+Run through testcases which run small parts of program.
+
+This is done in java using the j-unit testing framework.