002 Strategy Design Patterns

I. Overview

The strategy design pattern is to extract the realization of the function and form a unified interface.

Provides a unified interface parameter method.

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2. Code implementation

Here is an example of paying taxes.

[1] Policy interface

public  interface CalculateTax {
     // A unified interface, the input parameters of the method are salary and bonus 
    double calculate( double salary , double bouns);
}

[2] Implementation of the strategy

// A simple calculation method 
public  class SimpleStrategy implements CalculateTax{
    
    private static final double salary_ratio = 0.1d ; 
    private static final double bouns_ratio = 0.2d ; 
    //现在的计算方式
    public double calculate(double salary, double bouns) {
        return salary * salary_ratio + bouns * bouns_ratio;
    }
    
}

[3] call place

// tax calculator 
public  class TaxCalculator {
    
    // Calculate tax
     // The parameters of the method require a strategy to pass in 
    public  static  double countTax( double salary , double bouns ,CalculateTax strategy) {
         return strategy.calculate(salary, bouns);
    }
    
}

[4] Test

public class TestClass {
    
    public static void main(String[] args) {
        System.out.println(TaxCalculator.countTax(1000, 1000, new SimpleStrategy()));
    }
}

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3. Description 

(1) There are two cores of design patterns

　　　　[1] Policy interface

　　　　[2] Interface (abstract type) is used at the call site

(2) Benefits: When our strategy changes, we can program in a consistent way.

(3) When we use a framework like spring, we can use the configuration method to deal with it.

　　That is to say, when we need to modify, we only need to create a new class, and then modify the configuration to complete.