// patterns/strategy/StrategyPattern.java

// (c)2021 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 {

protected

Function<List<Double>, List<Double>> algorithm;

}

// The various strategies, each producing dummy data:

class LeastSquares extends FindMinima {

LeastSquares() {

// Line is a sequence of points:

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 strategy) {

this.strategy = strategy;

}

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 Perturbation());

System.out.println(solver.minima(line));

solver.changeAlgorithm(new Bisection());

System.out.println(solver.minima(line));

}

}

/* Output:

[1.1, 2.2]

[3.3, 4.4]

[5.5, 6.6]

*/