Adapter mode

When is the adapter mode

Adapter pattern （Adapter）： Convert the interface of a class into another interface that the client wants .Adapter Patterns enable classes that cannot work together because of interface incompatibility to work together .

UML

Adapter patterns are divided into object adapters and class adapters , Object adapters implement adaptation functions by composing aggregations , Class adapters implement functions by inheriting target classes and working classes .

Example code

package adapter;

public class test {
    
	public static void main(String[] args) {
    
		Target a=new Adapter();
		a.request();
		
	}
}

package adapter;

public abstract class Target {
    
	public abstract void request();
}

package adapter;

public class Adapter extends Target{
    
	private Adaptee adaptee;
	public  Adapter() {
    
		// TODO Auto-generated constructor stub
		adaptee=new Adaptee();
	}
	@Override
	public void request() {
    
		// TODO Auto-generated method stub
		adaptee.request();
	}
	
}

package adapter;

public class Adaptee {
    
	public void request(){
    
		System.out.println(" Real request ！");
	}
}

The following is from this blog

Use scenarios

1、 When you want to use a class , But when its interface is not compatible with other code , You can use adapter classes .

The adapter pattern allows you to create a middle tier class , It can be used as code and legacy classes 、 Converters between third-party classes or classes that provide weird interfaces .

2、 If you need to reuse such classes , They are in the same inheritance system , And they have some extra common methods , But these common methods are not common to all subclasses in this inheritance system .

You can extend each subclass , Add missing functionality to new subclasses . however , You have to add this code repeatedly in all new subclasses , This will make the code smell bad .
Adding missing functionality to an adapter class is a much more elegant solution . Then you can encapsulate the missing objects and functions in the adapter , Add adapter objects to this inheritance system , So as to dynamically obtain the required functions . If this is to work properly , The target class must have a common interface , The member variables of the adapter should follow this common interface . This way is the same as Decoration mode Very similar .

The relationship with other design patterns

• The bridge mode is usually designed in the early stage of development , Enables you to separate parts of the program for development . On the other hand , Adapter mode is usually used in existing programs , Let incompatible classes cooperate well .

• The adapter can modify the interface of existing objects , Decoration mode It can strengthen the object function without changing the object interface . Besides , Decoration also supports recursive composition , The adapter cannot achieve .

• Adapters can provide different interfaces for encapsulated objects , Proxy mode can provide the same interface for objects , Decoration can provide an enhanced interface for objects .

• Appearance mode Defines a new interface for an existing object , The adapter will try to use the existing interface . Adapters typically encapsulate only one object , Appearances usually act on the entire object subsystem .

• The bridge 、 The state pattern And strategy patterns （ To some extent, it includes adapters ） The interface of the pattern is very similar . actually , They are all based on Portfolio model —— Delegate work to other objects , But they also solved different problems . Patterns are not just recipes for organizing code in a particular way , You can also use them to discuss problems solved by patterns with other developers .