java oop abstraction methods code example

Example 1: abstraction in java

Abstraction is defined as hiding internal implementation and showing only 
necessary information.
// abstract class
abstract class Addition
{
   // abstract methods
   public abstract int addTwoNumbers(int number1, int number2);
   public abstract int addFourNumbers(int number1, int number2, int number3, int number4);
   // non-abstract method
   public void printValues()
   {
      System.out.println("abstract class printValues() method");
   }
}
class AbstractMethodExample extends Addition
{
   public int addTwoNumbers(int number1, int number2)
   {
      return number1 + number2;
   }
   public int addFourNumbers(int number1, int number2, int number3, int number4)
   {
      return number1 + number2 + number3 + number4;
   }
   public static void main(String[] args)
   {
      Addition add = new AbstractMethodExample();
      System.out.println(add.addTwoNumbers(6, 6));
      System.out.println(add.addFourNumbers(8, 8, 3, 2));
      add.printValues();
   }
}

Example 2: method abstraction

// Method abstraction is the practice of reducing inter-dependency between methods.  
 // The following is an unreasonably simple example, but the point stands: 
 // don't make the person on the other side of your function do more work 
 // than they need to.  Include all necessary data transformations in your 
 // methods as is.  For instance, take method GetAreaOfCircle: 

 // Good practice: 
float GetAreaOfCircle(float radius) {
	return 3.14f * radius * radius;
}
int main() {
	printf("%d", GetAreaOfCircle(3.0f));
    getch();
    return 0;
}

 // Bad practice: 
float GetAreaOfCircle(float radius) {
	return radius * radius;
}
int main() {
	float area = 3.14f * GetAreaOfCircle(3.0f);
	printf("%d", );
    getch();
    return 0;
}