Oracle certified java programmer level 2
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Sayed Ahmed Computer Engineering, BUET, Bangladesh Masters from the University of Manitoba, Canada Oracle Certified java programmer - level 2.

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Oracle Certified java programmer - level 2

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Sayed Ahmed

Computer Engineering, BUET, Bangladesh

Masters from the University of Manitoba, Canada

Oracle Certified java programmer - level 2

        Java Class Design        Advanced Class Design        Object-Oriented Design Principles        Generics and Collections        String Processing        Exceptions and Assertions        Java I/O Fundamentals        Java File I/O (NIO.2)        Building Database Applications with JDBC        Threads        Concurrency        Localization


Topics in detail


  • Their general recommendations are as follows:

    • Do favor defining classes over interfaces.

    • Do use abstract classes instead of interfaces to decouple the contract from implementations. Abstract classes, if defined correctly, allow for the same degree of decoupling between contract and implementation.

    • Do define an interface if you need to provide a polymorphic hierarchy of value types.

    • Consider defining interfaces to achieve a similar effect to that of multiple inheritance.

      • Chris Anderson expresses particular agreement with this last tenant, arguing that:

        • Abstract types do version much better, and allow for future extensibility, but they also burn your one and only base type. Interfaces are appropriate when you are really defining a contract between two objects that is invariant over time. Abstract base types are better for defining a common base for a family of types.

Inheritance vs interface vs abstract class


  • Use an interface if you want to define a contract. I.e. X must take Y and return Z. It doesn't care how the code is doing that. A class can implement multiple interfaces.

  • Use an abstract class if you want to define default behaviour in non-abstract methods so that the endusers can reuse it without rewriting it again and again. A class can extend from only one other class. An abstract class with only abstract methods can be as good definied as an interface. An abstract class without any abstract method is recognizeable as the Template Method pattern (see this answer for some real world examples).

  • An abstract class in turn can perfectly implement an interface whenever you want to provide the enduser freedom in defining the default behaviour.

Inheritance vs interface vs abstract class

Java Interfaces

Develop code that implements "is-a" and/or "has-a" relationships

Object Composition

OOP Design Principles

Design a class using the Singleton design pattern.


    • Use a Data Access Object (DAO) to abstract and encapsulate all access to the data source. The DAO manages the connection with the data source to obtain and store data.




Write code to implement the DAO pattern


    • The main difference between a "factory method" and an "abstract factory" is that the factory method is a single method, and an abstract factory is an object

    • there is an object A, who wants to make a Foo object. Instead of making the Foo object itself (e.g. with a factory method), it's going get a different object (the abstract factory) to create the Foo object.


Abstract Factory Method

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