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重构没有固定的形式，多年来我使用过不同的版本，并且我敢打赌不同的人也会有不同的版本。 该重构适用于这样的场景：switch语句块很大，并且会随时引入新的判断条件。这时，最好使用策略模式将每个条件封装到单独的类中。实现策略模式的方式是很多的。我在这里介绍的策略重构使用的是字典策略，这么做的好处是调用者不必修改原来的代码。
public class ClientCode {
public double CalculateShipping() {
ShippingInfo shippingInfo = new ShippingInfo();
return shippingInfo.CalculateShippingAmount(State.Alaska);
}
}
public enum State {
Alaska, NewYork, Florida
}
public class ShippingInfo {
public double CalculateShippingAmount(State shipToState) {
switch (shipToState) {
case State.Alaska:
return GetAlaskaShippingAmount();
case State.NewYork:
return GetNewYorkShippingAmount();
case State.Florida:
return GetFloridaShippingAmount();
default:
return 0d;
}
}
private double GetAlaskaShippingAmount() {
return 15d;
}
private double GetNewYorkShippingAmount() {
return 10d;
}
private double GetFloridaShippingAmount() {
return 3d;
}
}
public class ClientTest {
public Double CalculateShipping() {
ShippingInfo shippingInfo = new ShippingInfo();
return shippingInfo.CalculateShippingAmount(State.Alaska);
}
}
public enum State {
Alaska, NewYork, Florida
}
public class ShippingInfo {
private Dictionary<State, IShippingCalculation> ShippingCalculations;
public ShippingInfo() {
ShippingCalculations =new Hashtable<State, IShippingCalculation>();
ShippingCalculations.put(State.Alaska, new AlaskShippingCalculation());
ShippingCalculations.put(State.NewYork, new NewYorkShippingCalculation());
ShippingCalculations.put(State.Florida, new FloridaShippingCalculation());
}
public Double CalculateShippingAmount(State shipToState) {
return ShippingCalculations.get(shipToState).Calculate();
}
}
public interface IShippingCalculation {
Double Calculate();
}
public class AlaskShippingCalculation implements IShippingCalculation {
public Double Calculate () {
return 15d;
}
}
public class NewYorkShippingCalculation implements IShippingCalculation {
public Double Calculate () {
return 10d;
}
}
public class FloridaShippingCalculation implements IShippingCalculation {
public Double Calculate () {
return 3d;
}
}
public interface IShippingInfo {
Double CalculateShippingAmount(State state);
}
public class ClientCode {
public IShippingInfo ShippingInfo;
public Double CalculateShipping() {
return ShippingInfo.CalculateShippingAmount(State.Alaska);
}
}
public enum State{
Alaska, NewYork, Florida;
}
public class ShippingInfo implements IShippingInfo{
private Dictionary<State, IShippingCalculation> ShippingCalculations=new Hashtable<State, IShippingCalculation>();
public ShippingInfo(IShippingCalculation<State> shippingCalculations) {
for(State state:State.values()) {
ShippingCalculations.put(state, shippingCalculations);
}
}
public Double CalculateShippingAmount(State shipToState) {
return ShippingCalculations.get(shipToState).Calculate();
}
}
public interface IShippingCalculation<State> {
State getState();
Double Calculate();
}
public class AlaskShippingCalculation implements IShippingCalculation {
@Override
public State getState() {
return State.Alaska;
}
@Override
public Double Calculate() {
return 15d;
}
}
public class NewYorkShippingCalculation implements IShippingCalculation {
@Override
public State getState() {
return State.NewYork;
}
@Override
public Double Calculate() {
return 10d;
}
}
public class FloridaShippingCalculation implements IShippingCalculation {
@Override
public State getState() {
return State.Florida;
}
@Override
public Double Calculate() {
return 3d;
}
}
重构11-Switch to Strategy（Switch到策略模式）
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原文地址：http://www.cnblogs.com/jgig11/p/5786325.html
