Java 中的开放封闭设计原理
原文:https://www . geesforgeks . org/open-closed-design-principle-in-Java/
开放封闭设计原则是软件开发领域最重要的设计原则之一。这是一组 5 个设计原则的一部分，通常被称为首字母缩略词“固体”
S - Single Responsibility Principle
O - Open Closed Principle
L - Liskov Substitution Principle
I - Interface Segregation
D - Dependency Inversion
根据罗伯特·马丁的观点，这个原则规定软件实体(类、模块、函数)应该对扩展开放，对修改关闭。这意味着一个类应该足够灵活，以适应业务需求变化时的变化，而不会破坏现有的代码。因此，从属类不必改变。这最大限度地减少了测试工作，我们只需要关注新的代码更改。
方法:
基本上有两种实现接口的主要方式:
方法 1: 利用遗传
遵循这个原则的一个方法是使用继承。我们有一个超类，它被关闭进行修改，并且是基线的，是 jar 文件的一部分。任何想要修改超类行为的人都可以对其进行子类化、扩展和添加新特性。这确保了超类行为保持不变，并且超类的客户端不必进行代码更改。然而、继承引入了超类和子–类实现之间的紧密耦合。假设超类有缺陷或者超类版本有升级引入了代码变更，那么子类也需要修改。
例子:假设简开了一家面包店，并决定根据她的销售额保持简单和规模。
Java
// Java Program to Illustrate Open Closed Design Principle
// Using Inheritance
// Importing input output classes
import java.io.*;
// Class 1
// Helper class acting as parent class
class Cake {
// Member variable of Cake class
private int size;
private float weight;
// Constructor for cake which sets
// only size and dimension of cake
public Cake(int size, float weight)
{
// This keyword refers to current object itself
this.size = size;
this.weight = weight;
}
// Method
// To bake the cake
public void bake()
{
// Display message only
System.out.println(
"Baking cake with base as vanilla");
// Print and display the size and weight of the cake
System.out.println("Size is " + this.size
+ " inches and weight is "
+ this.weight + " kg.");
}
}
// Class 2
// Helper class(Child class) of class 1
class PineappleCake extends Cake {
// Member variables
private int size;
private float weight;
// Constructor
// To set the dimension of the pineapple cake
public PineappleCake(int size, float weight)
{
// Super keyword refers to parent class instance
super(size, weight);
// This keyword refer to current instance
this.size = size;
this.weight = weight;
}
// Method 1
// To decorate the pineapple cake
private void decorateCake()
{
// Display messages only
System.out.println("Decorating cake");
System.out.println("Adding pineapple pieces");
}
// Method 2
// To add cream to pineapple cake
private void addCream()
{
// Print statement
System.out.println("Adding white cream");
}
// Method 3
// To bake a pineapple cake
public void bake()
{
super.bake();
// Calling the above two methods created
addCream();
decorateCake();
// Print the dimension of the pineapple cake
System.out.println("Pineapple cake - " + this.size
+ " inches is ready");
}
}
// Class 3
// Helper class(Child class) of class 1
class ChocolateCake extends Cake {
// member variables
private int size;
private float weight;
// Constructor
// Setting the size nd weight of the chocolate cake
public ChocolateCake(int size, float weight)
{
super(size, weight);
this.size = size;
this.weight = weight;
}
// Method 1
// To decorate a chocolate cake
private void decorateCake()
{
// Display commands only
System.out.println("Decorating cake");
System.out.println("Adding chocolate chips");
}
// Method 2
// To add cream to chocolate cake
private void addCream()
{
// Print statement
System.out.println("Adding chocolate cream");
}
// Method 3
// to bake a chocolate cake
public void bake()
{
super.bake();
// Calling the above two methods created
addCream();
decorateCake();
// Print and display the dimension of chocolate cake
System.out.println("Chocolate cake - " + this.size
+ " inches is ready");
}
}
// Class 4
// Main class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an instance of pineapple cake
// int the main() method
// Custom dimension are passed as in arguments
PineappleCake pineappleCake
= new PineappleCake(7, 3);
// Calling the bake() method of PineappleCake class
// to bake the cake
pineappleCake.bake();
// Similarly, creating an instance of chocolate cake
// in the main() method
ChocolateCake chocolateCake
= new ChocolateCake(5, 2);
// Calling the bake() method of ChocolateCake class
// to bake the cake
chocolateCake.bake();
}
}
输出
Baking cake with base as vanilla
Size is 7 inches and weight is 3.0 kg.
Adding white cream
Decorating cake
Adding pineapple pieces
Pineapple cake - 7 inches is ready
Baking cake with base as vanilla
Size is 5 inches and weight is 2.0 kg.
Adding chocolate cream
Decorating cake
Adding chocolate chips
Chocolate cake - 5 inches is ready
输出说明:‘饼’类为基类。每个蛋糕的底部都有香草的味道。我们有两种特色菜，即菠萝和巧克力风味蛋糕。这些类使用 Cake 的 bake()方法制作香草蛋糕，然后添加奶油并根据口味装饰蛋糕。
注:之后几天，简氏面包店销量都很高。所以她决定烘焙不同口味的蛋糕，为顾客提供更多的品种。有了这些新的需求，我们需要改变‘Cake’类的构造函数，这样做上面代码中的变化就会体现出来。代码更改如下。然而，我们需要修改子类来接受第三个参数——代码工作的风格。
例:
爪哇
// Java Program to Illustrate Open Closed Design Principle
// Using Inheritance
// Alonside adding Parameter - Flavor to cakes
// Importing input output classes
import java.io.*;
// Class 1
// Helper class
// Acting as parent class
class Cake {
// Member variables
private int size;
private float weight;
// This is new declared variable to
// hold the flavour for the cake
private String flavor;
// Constructor
// To set the dimensions for the cake
public Cake(int size, float weight, String flavor)
{
this.size = size;
this.weight = weight;
// Here this keyword sets the
// current instance flavour to th cake
this.flavor = flavor;
}
// Method
// To bake the cake
public void bake()
{
// Printing the flavour of the desired cake
System.out.println("Baking cake with base as "
+ this.flavor);
// Printing the size and weight of the same cake
System.out.println("Size is " + this.size
+ " inches and weight is "
+ this.weight + " kg.");
}
}
// Class 2
// Helper class
class PineappleCake extends Cake {
// Member variables for the pineapple cake
private int size;
private float weight;
private String flavor;
// Constructor
// Updated as per requirements as sales rise flavour is
// added, so do setting the flavour
public PineappleCake(int size, float weight,
String flavor)
{
// Super keyword refers to parent class
super(size, weight, flavor);
// This keyword refers to current instance
this.size = size;
this.weight = weight;
this.flavor = flavor;
}
// Method 1
// To decorate the cake
private void decorateCake()
{
// Display commands only
System.out.println("Decorating cake");
System.out.println("Adding pineapple pieces");
}
// Method 2
// To add cream to the flavored pineapple cake
private void addCream()
{
System.out.println("Adding white cream");
}
// Method 3
// To bake a flavored pineapple cake
public void bake()
{
// Super keyword calls the Cake class bake() method
super.bake();
// Calling the above two methods
addCream();
decorateCake();
// Printing the dimensions of
// flavoured pineapple cake
System.out.println("Pineapple cake - " + this.size
+ " inches is ready");
}
}
// Similarly setting the same for
// the 'flavoured' chocolate cake
// Class 3
// Helper class (Base class of parent class)
class ChocolateCake extends Cake {
private int size;
private float weight;
private String flavor;
// Updated constructor
public ChocolateCake(int size, float weight,
String flavor)
{
super(size, weight, flavor);
this.size = size;
this.weight = weight;
this.flavor = flavor;
}
// Method 1
// To decorate the flavored chocolate cake
private void decorateCake()
{
System.out.println("Decorating cake");
System.out.println("Adding chocolate chips");
}
// Method 2
// To add cream to the flavoured chocolate cake
private void addCream()
{
System.out.println("Adding chocolate cream");
}
// Method 3
// To bake a flavoured chocolate cake
public void bake()
{
super.bake();
addCream();
decorateCake();
System.out.println("Chocolate cake - " + this.size
+ " inches is ready");
}
}
// Class 4
// Main class
class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating a pineapple cake in the main() method
// Custom dimensions are passed as in arguments
PineappleCake pineappleCake
= new PineappleCake(7, 3, "vanilla");
// Calling the bake() method of the PineappleCake
// Class to bake the pinelapple cake
pineappleCake.bake();
// Similarly repeating the same with the chocolate
// cake
// Creating a chocolate cake by creating an object
// of ChocolateCake class in the main method
ChocolateCake chocolateCake
= new ChocolateCake(5, 2, "chocolate");
// Calling the bake() method of the ChocolateCake
// Class to bake the chocolate cake
chocolateCake.bake();
}
}
输出
Baking cake with base as vanilla
Size is 7 inches and weight is 3.0 kg.
Adding white cream
Decorating cake
Adding pineapple pieces
Pineapple cake - 7 inches is ready
Baking cake with base as chocolate
Size is 5 inches and weight is 2.0 kg.
Adding chocolate cream
Decorating cake
Adding chocolate chips
Chocolate cake - 5 inches is ready
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