A Simple Example with a Class and 1 Object

As I am a retired COBOL programmer, I don’t know anything about Object Oriented programming so please forgive me if this example seems a bit elementary. Classes are templates for real-life objects. In the example below, a Rectangle class is created. Each object in this class (i.e. each rectangle) has a width and a height. These are called instance variables. An object called my_rectangle is created in the Rectangle class and its width and height are supplied. Finally, a variable called area is created, calculated and displayed:

 

Java > cat Rectangle.java

class Rectangle

  {

  double width;

  double height;

  }

class RectangleExample

  {

  public static void main(String args[])

    {

    Rectangle my_rectangle = new Rectangle();

    double area;

    my_rectangle.width = 3;

    my_rectangle.height = 4;

    area = my_rectangle.width * my_rectangle.height;

    System.out.println("Area = " + area);

    }

  }

Java > javac Rectangle.java

Java > java RectangleExample

Area = 12.0

Java >

Java Modulus Operator

Many programming languages have a modulus operator, which allows you to calculate the remainder left over after a division. If I remember correctly, COBOL actually used the word REMAINDER to allow you to do this. In Java, you use the percent symbol as shown below:

UBUNTU > cat prog26.java
public class prog26
{
public static void main (String args[])
  {
  System.out.println
  ("17/5 = " + (int) 17/5 + " remainder " + 17%3);
  System.out.println
  ("15/2 = " + (int) 15/2 + " remainder " + 15%2);
  }
}

UBUNTU > javac prog26.java

UBUNTU > java prog26

17/5 = 3 remainder 2

15/2 = 7 remainder 1

UBUNTU > 

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