Main.java

interface ICalculatingStrategy{
	public int calculate(int a, int b);
}

class CalculatingStrategyFactory{
	public static ICalculatingStrategy create(String strategy){
		switch(strategy) {
			case "add": return new ICalculatingStrategy(){
				public int calculate(int a, int b) {
					return a + b;
				}
			};
			case "multiply": return new ICalculatingStrategy(){
				public int calculate(int a, int b) {
					return a * b;
				}
			};
			default: throw new IllegalArgumentException("Unsupported strategy");
		}
	}
}

public class Main{
	public static void main(String...args){
		System.out.println(
			CalculatingStrategyFactory.create("multiply").calculate(3, 2)
		);
	}
}