69 lines
1.7 KiB
Java
69 lines
1.7 KiB
Java
// patterns/strategy/StrategyPattern.java
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// (c)2021 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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// {java patterns.strategy.StrategyPattern}
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package patterns.strategy;
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import java.util.function.*;
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import java.util.*;
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// The common strategy base type:
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class FindMinima {
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protected
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Function<List<Double>, List<Double>> algorithm;
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}
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// The various strategies, each producing dummy data:
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class LeastSquares extends FindMinima {
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LeastSquares() {
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// Line is a sequence of points:
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algorithm = (line) -> Arrays.asList(1.1, 2.2);
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}
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}
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class Perturbation extends FindMinima {
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Perturbation() {
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algorithm = (line) -> Arrays.asList(3.3, 4.4);
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}
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}
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class Bisection extends FindMinima {
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Bisection() {
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algorithm = (line) -> Arrays.asList(5.5, 6.6);
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}
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}
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// The "Context" controls the strategy:
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class MinimaSolver {
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private FindMinima strategy;
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MinimaSolver(FindMinima strategy) {
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this.strategy = strategy;
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}
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List<Double> minima(List<Double> line) {
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return strategy.algorithm.apply(line);
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}
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void changeAlgorithm(FindMinima newAlgorithm) {
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strategy = newAlgorithm;
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}
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}
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public class StrategyPattern {
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public static void main(String[] args) {
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MinimaSolver solver =
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new MinimaSolver(new LeastSquares());
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List<Double> line = Arrays.asList(
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1.0, 2.0, 1.0, 2.0, -1.0,
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3.0, 4.0, 5.0, 4.0 );
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System.out.println(solver.minima(line));
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solver.changeAlgorithm(new Perturbation());
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System.out.println(solver.minima(line));
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solver.changeAlgorithm(new Bisection());
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System.out.println(solver.minima(line));
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}
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}
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/* Output:
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[1.1, 2.2]
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[3.3, 4.4]
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[5.5, 6.6]
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*/
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