Example for an implentation of the DAO Pattern from http://java-latte.blogspot.de/2014/02/the-data-access-object-dao-design.html

DAO Pattern.java

/*  
  * Transfer Object as per diagram  
  */  
 public class CircleTransfer{  
      private int x;  
      private int y;  
      private int radius;  
      void setX(int x){  
           this.x=x;  
      }  
      void setY(int y){  
           this.y=y;  
      }  
      int getX(){  
           return x;  
      }  
      int getY(){  
           return y;  
      }  
      void setRadius(int radius){  
           this.radius=radius;  
      }  
      int getRadius(){  
           return radius;  
      }  
 }  
 /*  
  * DAO as per Diagram  
  */  
 interface CircleDAO{  
      public void insertCircle(CircleTransfer circle);  
      public CircleTransfer findCircle(int x,int y);  
      public void deleteCircle(int x,int y);  
 }  
 /**  
  * DataSource as per Diagram  
  * Oracle Implementation  
  */  
 public class RDMSDAO implements CircleDAO{  
      @Override  
      public void insertCircle(CircleTransfer circle) {  
           // insertCircle implementation as per Oracle database  
      }  
      @Override  
      public CircleTransfer findCircle(int x, int y) {  
           // findCircle implementation  
           return null;  
      }  
      @Override  
      public void deleteCircle(int x, int y) {  
           // deleteCircle implemenation  
      }  
 }  
 /**  
  * DataSource as per Diagram  
  * MySql Implementation  
  */  
 public class MYSQLDAO implements CircleDAO{  
      @Override  
      public void insertCircle(CircleTransfer circle) {  
           // insertCircle implementation as per MYSQL database  
      }  
      @Override  
      public CircleTransfer findCircle(int x, int y) {  
           // findCircle implementation  
           return null;  
      }  
      @Override  
      public void deleteCircle(int x, int y) {  
           // deleteCircle implemenation  
      }       
 }  
 /*  
  * Factory   
  */  
 public class DAOFactory{  
      public static CircleDAO getCircleDao(String sourceType){  
           switch(sourceType){  
           case "Oracle":  
                return new RDMSDAO();  
           case "mysql":  
                return new MYSQLDAO();  
           }  
           return null;  
      }  
 }  
 /*  
  * Core Business logic  
  */  
 public class Circle{  
      private int x,y,r;  
      Circle(int x,int y, int r){  
           this.x=x;  
           this.y=y;  
           this.r=r;  
      }  
      public CircleTransfer getCircleTransferObject(){  
           CircleTransfer c = new CircleTransfer();  
           c.setRadius(r);  
           c.setX(x);  
           c.setY(y);  
           return c;  
      }  
 }  
 /*  
  * Client  
  */  
 public class DaoPatternDemo {  
      public static void main(String[] javalatte) {  
           Circle c = new Circle(2,2,4);  
           CircleTransfer ct = c.getCircleTransferObject();  
           CircleDAO cDao = DAOFactory.getCircleDao("oracle");  
           cDao.insertCircle(ct);  
      }  
 }