2. Java 7: Design Patterns

Question 1

What are the Java 7 design patterns you need to know?

Answer 1

• Singleton pattern
• Composition pattern
• DAO pattern
• Factory pattern

Question 2

What are two ways to make the Sinlgeton pattern thread-safe?

Answer 2

• Make the whole getInstance method synchronized (performance impact because it will always enter a synchronized method)
• Add a synchronized block to the getInstance methodm (less performance impact) f.e:

MySingleton getInstance() {
   if(instance == null) {
      synchronized(MySingleton.class) {
         if(instance == null) { instance = new MySingleton(); }
      }
   }
   return instance;
}

Question 3

How can be tested if TypeB needs inheritance?

Answer 3

Does TypeB want to expose the complete interface of TypeA so that TypeB van be used where TypeA is expected?

Question 4

How can be tested if TypeB needs composition?

Answer 4

Does TypeB only want some part of the behaviour of TypeA exposed?

Question 5

What is a DAO?

Answer 5

Data Access Object. An object that provides a abstract interface to some type of database or persistence layer.