设计模式之策略模式

在策略模式（Strategy Pattern）中，一个类的行为或其算法可以在运行时更改。这种类型的设计模式属于行为型模式。

在策略模式中，我们创建表示各种策略的对象和一个行为随着策略对象改变而改变的 context 对象。策略对象改变 context 对象的执行算法。

UML图

示例代码

<?php

class StrategyContext {
    private $strategy = NULL; 
    //bookList is not instantiated at construct time
    public function __construct($strategy_ind_id) {
        switch ($strategy_ind_id) {
            case "C": 
                $this->strategy = new StrategyCaps();
            break;
            case "E": 
                $this->strategy = new StrategyExclaim();
            break;
            case "S": 
                $this->strategy = new StrategyStars();
            break;
        }
    }
    public function showBookTitle($book) {
      return $this->strategy->showTitle($book);
    }
}

interface StrategyInterface {
    public function showTitle($book_in);
}
 
class StrategyCaps implements StrategyInterface {
    public function showTitle($book_in) {
        $title = $book_in->getTitle();
        $this->titleCount++;
        return strtoupper ($title);
    }
}

class StrategyExclaim implements StrategyInterface {
    public function showTitle($book_in) {
        $title = $book_in->getTitle();
        $this->titleCount++;
        return Str_replace(' ','!',$title);
    }
}

class StrategyStars implements StrategyInterface {
    public function showTitle($book_in) {
        $title = $book_in->getTitle();
        $this->titleCount++;
        return Str_replace(' ','*',$title);
    }
}

class Book {
    private $author;
    private $title;
    function __construct($title_in, $author_in) {
        $this->author = $author_in;
        $this->title  = $title_in;
    }
    function getAuthor() {
        return $this->author;
    }
    function getTitle() {
        return $this->title;
    }
    function getAuthorAndTitle() {
        return $this->getTitle() . ' by ' . $this->getAuthor();
    }
}

// testing

  writeln('BEGIN TESTING STRATEGY PATTERN');
  writeln('');

  $book = new Book('PHP for Cats','Larry Truett');
 
  $strategyContextC = new StrategyContext('C');
  $strategyContextE = new StrategyContext('E');
  $strategyContextS = new StrategyContext('S');
 
  writeln('test 1 - show name context C');
  writeln($strategyContextC->showBookTitle($book));
  writeln('');

  writeln('test 2 - show name context E');
  writeln($strategyContextE->showBookTitle($book));
  writeln('');
 
  writeln('test 3 - show name context S');
  writeln($strategyContextS->showBookTitle($book));
  writeln('');

  writeln('END TESTING STRATEGY PATTERN');

  function writeln($line_in) {
    echo $line_in."<br/>";
  }