I want to reference an enum method to retrieve the class of an algorithm so that I can lazy-load a new instance of the algorithm for use in the strategy design pattern.
In this example, I am using an enum to reference three different strategy classes that calculate Fibonacci numbers: RecursiveFibonacciGenerator, IterativeFibonacciGenerator, and MemoizedFibonacciGenerator (all of which inherit from FibonacciGenerator).
The code (with lines generating errors commented with intent) is as follows:
package com.example.strategy;
public class Fibonacci {
private enum Algorithm {
RECURSIVE (RecursiveFibonacciGenerator.class),
ITERATIVE (IterativeFibonacciGenerator.class),
MEMOIZED (MemoizedFibonacciGenerator.class);
private final Class<T> algorithmClass; // Declare class of same type as constructor
private final T instance; // Declare instance of class defined in constructor
private <T extends FibonacciGenerator> Algorithm(Class<T> algorithmClass) {
this.algorithmClass = algorithmClass;
}
public T getInstance() {
if (this.instance == null) {
this.instance = this.algorithmClass.newInstance();
}
return this.instance;
}
}
public Integer getTerm(Integer termNumber) {
profileGenerator(termNumber, Algorithm.RECURSIVE);
profileGenerator(termNumber, Algorithm.ITERATIVE);
return profileGenerator(termNumber, Algorithm.MEMOIZED);
}
private Integer profileGenerator(Integer termNumber, Algorithm algorithm) {
System.out.print("Computing term using " + algorithm.toString() + " algorithm... ");
Long startTimeMilliseconds = System.currentTimeMillis();
Integer term = algorithm.getInstance().generateTerm(termNumber);
Long endTimeMilliseconds = System.currentTimeMillis();
Long computationTimeMilliseconds = endTimeMilliseconds - startTimeMilliseconds;
System.out.println("term computed in " + computationTimeMilliseconds + " milliseconds");
}
}
I would like to know how I can use this enum constructor to store a member variable of the Class<T> type.
Edit: Added full code to clarify intent
Answer
public enum Algorithm {
RECURSIVE(FibonacciGenerator.RecursiveFibonacciGenerator.class),
ITERATIVE(FibonacciGenerator.IterativeFibonacciGenerator.class),
MEMOIZED(FibonacciGenerator.MemoizedFibonacciGenerator.class);
private final Class<? extends FibonacciGenerator> algorithmClass;
private <T extends FibonacciGenerator> Algorithm(Class<T> algorithmClass) {
this.algorithmClass = algorithmClass;
}
}
Does that do what you want?
The other option is to use an instance of the class, but after further thought I think this is a bad idea. If you are going to use an instance of the class then why’d you need the enum in the first place?