Factory Pattern (Factory Method Pattern)
The factory method pattern is a creational pattern. It deals with the problem of creating objects without specifying the exact
class of object that will be created. Lets brief this, in real programing world, we need to create different objects with similar functionality.
Lets say, we need Currency objects based on country. Now you define an interface called Currency, and specify your functionality in the form of
method. Now implement this interface for different countries, and each method implementation will be specific to the country.
Now how can I create objects? Create a factory class and provide a static method to get required object. This method should take
input, here input can be country name. Based on the country value, create specific country object, and return it. In this page you can see java code example
for this.
Now lets come to the definitions: the factory method pattern is a creational pattern which uses factory methods to deal with the problem of
creating objects without specifying the exact class of object that will be created. This is done by creating objects via a factory method, which is either
specified in an interface and implemented in implementing classes (concrete classes); or implemented in a base class, which can be overridden when inherited
in derived classes; rather than by a constructor.
Here is the Currency Interface
package com.java2novice.dp.factory;
public interface Currency {
public String getCurrency();
public String getSymbol();
}
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Implementation class for Indian Currency
package com.java2novice.dp.factory;
public class India implements Currency{
@Override
public String getCurrency() {
return "Rupee";
}
@Override
public String getSymbol() {
return "Rs";
}
public static void main(String a[]){
India in = new India();
System.out.println(in.getSymbol());
}
}
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Implementation class for USA Currency
package com.java2novice.dp.factory;
public class USA implements Currency{
@Override
public String getCurrency() {
return "Dollar";
}
@Override
public String getSymbol() {
return "$";
}
}
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Factory class to create objects
package com.java2novice.dp.factory;
public class CurrencyFactory {
public static Currency getCurrencyByCountry(String cnty) throws Exception{
if("IN".equalsIgnoreCase(cnty)){
return new India();
} else if("USA".equalsIgnoreCase(cnty)){
return new USA();
}
throw new Exception("Invalid country...");
}
public static void main(String a[]){
Currency india;
try {
india = CurrencyFactory.getCurrencyByCountry("IN");
System.out.println("Indian currency: "+india.getCurrency());
System.out.println("Indian currency symbol: "+india.getSymbol());
} catch (Exception e) {
e.printStackTrace();
}
}
}
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