How to avoid multiple if else using design patterns.

Question

Hi,
Which design patterns is used to avoid lot of if else in our code . Say for example if the user press 1 the out put should be one, if he press 2 it should be two like this upto 10. So we need to include lot of if-else part. How to avoid the multiple if else using design patter for this scenario. I can't find the solution for this problem can you guys help me?.

Answer 1

I'm too lazy to read a whole text book, but the first google link provides a code sample which made me laugh.
http://www.refactoring.com/catalog/replaceConditionalWithPolymorphism.html
  double getSpeed() {
    switch (_type) {
      case EUROPEAN:
        return getBaseSpeed();
      case AFRICAN:
        return getBaseSpeed() - getLoadFactor() * _numberOfCoconuts;
      case NORWEGIAN_BLUE:
        return (_isNailed) ? 0 : getBaseSpeed(_voltage);
    throw new RuntimeException ("Should be unreachable");
  }My implementation of The Bridge Over The Parrot Shop
package forums;
import java.util.Random;
abstract class Bird {
  private static final Random random = new Random();
  abstract double getAirSpeed();
  public double getBaseSpeed() {
    return randomDouble(18.96);
  protected static double randomDouble(double max) {
    return random.nextDouble() * max;
  protected static int randomInt(int max) {
    return random.nextInt(max);
class EuropeanSwallow extends Bird {
  double getAirSpeed() {
    return getBaseSpeed();
class AfricanSwallow extends Bird {
  private int _numberOfCoconuts;
  public AfricanSwallow() {
    this(randomInt(4));
  public AfricanSwallow(int numberOfCoconuts) {
    _numberOfCoconuts = numberOfCoconuts;
  double getAirSpeed() {
    return getBaseSpeed() - getLoadFactor() * _numberOfCoconuts;
  public double getLoadFactor() {
    return randomDouble(3.12);
class NorwegianBlue extends Bird {
  private boolean _isNailed;
  private double _voltage;
  public NorwegianBlue() {
    this(randomInt(10)<2, randomDouble(12.0));
  public NorwegianBlue(boolean isNailed, double voltage) {
    _isNailed = isNailed;
    _voltage = voltage;
  double getAirSpeed() {
    return _isNailed ? 0 : getBaseSpeed(_voltage);
  double getBaseSpeed(double voltage) {
    return getBaseSpeed() * (1+(voltage/Math.PI));
public class AirSpeedTest
  public static void main(String[] args)
    System.out.println("EUROPEAN: "+new EuropeanSwallow().getAirSpeed());
    System.out.println("AFRICAN: "+new AfricanSwallow().getAirSpeed());
    System.out.println("NORWEGIAN_BLUE: "+new NorwegianBlue().getAirSpeed());
}... and the requisite background for the uninitiated [NORWEGIAN_BLUE|http://www.youtube.com/watch?v=4vuW6tQ0218] and [EUROPEAN v AFRICAN|http://www.youtube.com/watch?v=4b4bGAoVR7g].
You have to know these things when you're a King you know.
Cheers. Keith.