OnJava8-Examples/patterns/chain/ChainOfResponsibility.java

// patterns/chain/ChainOfResponsibility.java
// (c)2020 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.
// Using the Functional interface
// {java patterns.chain.ChainOfResponsibility}
package patterns.chain;
import java.util.*;
import java.util.function.*;

class Result {
  boolean success;
  List<Double> line;
  Result(List<Double> data) {
    success = true;
    line = data;
  }
  Result() {
    success = false;
    line = Collections.<Double>emptyList();
  }
}

class Fail extends Result {}

interface Algorithm {
  Result algorithm(List<Double> line);
}

class FindMinima {
  public static Result leastSquares(List<Double> line) {
    System.out.println("LeastSquares.algorithm");
    boolean weSucceed = false;
    if(weSucceed) // Actual test/calculation here
      return new Result(Arrays.asList(1.1, 2.2));
    else // Try the next one in the chain:
      return new Fail();
  }
  public static Result perturbation(List<Double> line) {
    System.out.println("Perturbation.algorithm");
    boolean weSucceed = false;
    if(weSucceed) // Actual test/calculation here
      return new Result(Arrays.asList(3.3, 4.4));
    else
      return new Fail();
  }
  public static Result bisection(List<Double> line) {
    System.out.println("Bisection.algorithm");
    boolean weSucceed = true;
    if(weSucceed) // Actual test/calculation here
      return new Result(Arrays.asList(5.5, 6.6));
    else
      return new Fail();
  }
  static List<Function<List<Double>, Result>>
    algorithms = Arrays.asList(
      FindMinima::leastSquares,
      FindMinima::perturbation,
      FindMinima::bisection
    );
  public static Result minima(List<Double> line) {
    for(Function<List<Double>, Result> alg :
        algorithms) {
      Result result = alg.apply(line);
      if(result.success)
        return result;
    }
    return new Fail();
  }
}

public class ChainOfResponsibility {
  public static void main(String[] args) {
    FindMinima solver = new FindMinima();
    List<Double> line = Arrays.asList(
      1.0, 2.0, 1.0, 2.0, -1.0,
      3.0, 4.0, 5.0, 4.0);
    Result result = solver.minima(line);
    if(result.success)
      System.out.println(result.line);
    else
      System.out.println("No algorithm found");
  }
}
/* Output:
LeastSquares.algorithm
Perturbation.algorithm
Bisection.algorithm
[5.5, 6.6]
*/