Jon Rumsey

An online markdown blog and knowledge repository.

Project maintained by nojronatron Hosted on GitHub Pages — Theme by mattgraham

OOP Classes Binary Decimal Hexidecimal

Reading Materials

OOP Principles - Oracle Docs

Object Oriented Programming Principles by Oracle

What Is An Object?

Characteristics of objects: State and behavior.

State: What an object is, or the data it stores, e.g. React State.
Behavior: What an object can do, or the capabilities is has, e.g. React Render or Callback Functions.

""" Bundling code into individual software objects provides...benefits:

Modularity: Write and maintain code independently of other objects or code pages.
Information Hiding: Details of internal implementation are hidden from outside world.
Re-use: Use existing objects in your program.
Pluggability and debugging ease: If a particular object turns out to be problematic...remove it from your app and plug in a different object as its replacement.
"""

All above skimmed from [Oracle Docs (see link above)]

What Is A Class?

Objects are built using a Class to create individual instances.
Define a Class from which many Object Instances can be created without writing much code.

What Is Inheritance?

Common details between objects can be identified between them.
There is no need to re-write the same properties or methods for classes that share those same members.
Instead inheritance allows creating Classes which reusing existing "parent class" members.
Inheritance enables creating a single "parent" or "root" class, then creating "child" classes that automatically get access to Members from their parent class.
Reduces code writing.
Enables rapid object instantiation.
Keyword: EXTENDS.

class ParentClass {
  ...
}
class ChildClass extends ParentClass {
  ...
}

What Is An Interface?

An interface describes required Methods that a Class guarantees will be implemented.
I have heard in the past that Interfaces can be considered "contracts" so the code knows what capabilities a Class will have.
Keyword: IMPLEMENTS.

interface Parent {
  // the following methods are not implemented
  // the members must still define a return type and any strongly types parameters
  void methodOne();
  void methodTwo(int number);
  String methodThree();
  Boolean isMethodFour(Double bigNum);
}
class MyParent implements Parent {
  public void methodOne() {...};
  public void methodTwo(int number){...};
  public String methodThree(){ return "Returning a String"; };
  public Boolean isMethodFour(Double bigNum) { return bigNum > 0;};
}

What Is A Package?

""" ...is a namespace that organizes a set of related classes and interfaces. """

The above is skimmed from [Oracle Docs (see link at head of this section)]

Libraries are called "Application Programming Interfaces" or APIs.
Many files and entire directory hierarchies can be stored in packages to define a set of state and functionality that other Applications can make use of.

Note: There is an entire Oracle website dedicated to the Java SE 8 API Specification

About getClass() and .class

The getClass method: objectInstance.getClass()
Using any direct instance of objectInstance, '.getClass()' returns the Class from which the instance was instantiated.
Per Oracle's documentation: "Returns the runtime class of this Object."

The .class property: ObjectType.class
Returns an Object that represents the ObjectType class.

There is interesting conversation about these members in this StackOverflow discussion

Both members are defined within API java.lang.Object, the top Class in the Java hierarchy.

See Oracle's documentation on Java Classes for more details.

Documentation of Spring and a few HTTP-oriented libraries we've looked at recently.

Reference: Classes Discussion

Classes discussion by Oracle

Binary Decimal and Hexadecimal

Binary, Decimal, and Hexidecimal reading by MathIsFun

Decimals are 10-base numbers.
Digits have positions, arranged around a decimal point.
Every position is 10x bigger to the left, or 1/10th the value to the right of the decimal.

Different Number Systems

Other number systems count using a base other than 10.
Hexadecimal numbers are base-16.
Binary numbers are base-2.
Regardless of the numbering system, once you know the base, you know when to "carry a one" by this algorithm:

while: number % base_system != 0 {
  increment: +1
}
shift: stack a 1 in the 2nd digit position and reset the 2nd digit position to 0

Hexadecimal

A base-16 system.
Numbers are 0-9 with A-F for the 11th through 16th values.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F

Convert Hexadecimal to Decimal Algorithm

Source Permandi.com FP HTML Tips

Get the last digit of the hexideciaml number and call this digit the current digit.
Make a variable called power and set it to 0.
Multiply the current digit with 16^power and store the result.
Increment power by 1.
Set the current digit to the previous digit of the hexadecimal number.
Repeat steps 3 through 5 until all digits have been multiplied.
Sum all of the result of step 4 to get the answer.

Convert Decimal to Hexadecimal Algorithm