OnJava8-Examples/patterns/strategy/StrategyPattern2.java

// patterns/strategy/StrategyPattern2.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.StrategyPattern2}
package patterns.strategy;
import java.util.function.*;
import java.util.*;

// "Context" is now incorporated:
class FindMinima2 {
  private
  Function<List<Double>, List<Double>> algorithm;
  FindMinima2() { leastSquares(); } // default
  // The various strategies:
  void leastSquares() {
    algorithm = (line) -> Arrays.asList(1.1, 2.2);
  }
  void perturbation() {
    algorithm = (line) -> Arrays.asList(3.3, 4.4);
  }
  void bisection() {
    algorithm = (line) -> Arrays.asList(5.5, 6.6);
  }
  List<Double> minima(List<Double> line) {
    return algorithm.apply(line);
  }
}

public class StrategyPattern2 {
  public static void main(String[] args) {
    FindMinima2 solver = new FindMinima2();
    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.perturbation();
    System.out.println(solver.minima(line));
    solver.bisection();
    System.out.println(solver.minima(line));
  }
}
/* Output:
[1.1, 2.2]
[3.3, 4.4]
[5.5, 6.6]
*/