// patterns/strategy/StrategyPattern.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// {java patterns.strategy.StrategyPattern}
package patterns.strategy;
import java.util.function.*;
import java.util.*;

// The common strategy base type:
class FindMinima {
 Function<List<Double>, List<Double>> algorithm;
}

// The various strategies:
class LeastSquares extends FindMinima {
 LeastSquares() {
 // Line is a sequence of points (Dummy data):
 algorithm = (line) -> Arrays.asList(1.1, 2.2);
 }
}

class Perturbation extends FindMinima {
 Perturbation() {
 algorithm = (line) -> Arrays.asList(3.3, 4.4);
 }
}

class Bisection extends FindMinima {
 Bisection() {
 algorithm = (line) -> Arrays.asList(5.5, 6.6);
 }
}

// The "Context" controls the strategy:
class MinimaSolver {
 private FindMinima strategy;
 MinimaSolver(FindMinima strat) {
 strategy = strat;
 }
 List<Double> minima(List<Double> line) {
 return strategy.algorithm.apply(line);
 }
 void changeAlgorithm(FindMinima newAlgorithm) {
 strategy = newAlgorithm;
 }
}

public class StrategyPattern {
 public static void main(String[] args) {
 MinimaSolver solver =
 new MinimaSolver(new LeastSquares());
 List<Double> line = Arrays.asList(
 1.0, 2.0, 1.0, 2.0, -1.0,
 3.0, 4.0, 5.0, 4.0 );
 System.out.println(solver.minima(line));
 solver.changeAlgorithm(new Bisection());
 System.out.println(solver.minima(line));
 }
}
/* Output:
[1.1, 2.2]
[5.5, 6.6]
*/