Java Programming - Object-Oriented Design

Object-Oriented Design

• Focuses on designing classes and objects in Java programming.

Interfaces

• A Java interface is a collection of abstract methods and constants.
• Methods in an interface:
  • An abstract method has no body.
  • All methods are public by default.
  • Cannot be instantiated, only implemented.
• A class implements an interface by:
  • Stating it in the class header.
  • Defining all abstract methods.
• Example:

  public interface Doable {
      void doThis();
      int doThat();
      void doThis2(double value, char ch);
      boolean doTheOther(int num);
  }

Implementation Example

• Class implementing an interface example:

  public class CanDo implements Doable {
      public void doThis() { /* implementation */ }
      public int doThat() { /* implementation */ }
      // other methods
  }

• A class can implement multiple interfaces.

Common Interfaces in Java

• Comparable:
  • Contains the abstract method compareTo for object comparison.
  • Can return negative, zero, or positive values.
• Iterator:
  • Provides methods: hasNext, next, and remove for iterating collections.
• Iterable:
  • Has a method iterator to return an Iterator object.

Enumerated Types

• Define a new data type with a list of possible values.
• Example:

  enum Season { winter, spring, summer, fall }

• Can have methods and additional properties:

  public enum Season {
      winter("Dec-Feb"), spring("Mar-May");
      private String span;
      Season(String months) { this.span = months; }
      public String getSpan() { return span; }
  }

• Every enumerated type has a static method values that lists all values for that type, usable in loops.

Summary

• Interfaces and enumerated types are fundamental to object-oriented design in Java, allowing for well-structured code and type safety.