Design Pattern (10) Strategy Pattern

What is the strategy pattern

Strategy pattern is a behavioral design pattern. The purpose of any program is to solve a problem. In order to solve the problem, we need to write a specific algorithm, and the strategy mode can replace the algorithm as a whole.

example:

There are also examples of strategy patterns in java, such as functional interfaces and lambda expressions

Example: convert string case

StringPrintStragegy strategy interface

package BehavioralPattern.StrategyMode;

/**
 * 字符串打印策略
 */

public interface StringPrintStragegy {
    
    
    /**
     * 字符串转换
     */
    String changeString(String s);
}

ToLowerCaseStragegy string to lowercase strategy

package BehavioralPattern.StrategyMode;

/**
 * 字符串转小写
 */

public class ToLowerCaseStragegy implements StringPrintStragegy{
    
    
    @Override
    public String changeString(String s) {
    
    
        return s.toLowerCase();
    }
}

ToUpperCaseStragegy string to uppercase strategy

package BehavioralPattern.StrategyMode;

/**
 * 字符串转大写
 */

public class ToUpperCaseStragegy implements StringPrintStragegy{
    
    
    @Override
    public String changeString(String s) {
    
    
        return s.toUpperCase();
    }
}

StringChangeTool string conversion tool (use strategy)

package BehavioralPattern.StrategyMode;

/**
 * 字符串转换工具
 */

public class StringChangeTool {
    
    

    private StringPrintStragegy stragegy;

    public StringChangeTool(StringPrintStragegy stragegy) {
    
    
        this.stragegy = stragegy;
    }

    public String change(String s){
    
    
        return stragegy.changeString(s);
    }
}

Main

package BehavioralPattern.StrategyMode;

/**
 * Main
 */

public class Main {
    
    
    public static void main(String[] args) {
    
    
        String s = "HelLo WoRld";
        //使用策略
        StringChangeTool lowerTool = new StringChangeTool(new ToLowerCaseStragegy());
        StringChangeTool upperTool = new StringChangeTool(new ToUpperCaseStragegy());
        System.out.println(lowerTool.change(s));
        System.out.println(upperTool.change(s));
    }
}

result

Summarize

The core idea of ​​the strategy pattern is to extract the algorithm that is easy to change in a calculation method and pass it in as a "strategy" parameter, so that the new strategy does not need to modify the original logic. The strategy pattern is also a good replacement for if-else in code.

Different from template method mode:
template method mode --------- the whole process
strategy mode --------- a specific algorithm in the process