(2022.1.31-2022.2.14) template mode analysis

In template mode （Template Pattern） in , An abstract class publicly defines how to execute its methods / Templates . Its subclass can override method implementation as needed , But the call will take place in the way defined in the abstract class . This type of design pattern belongs to behavioral pattern .

Introduce
Intention ： Defines the skeleton of an algorithm in an operation , Instead, defer some steps to subclasses . The template approach allows subclasses to redefine certain steps of an algorithm without changing its structure .

Main solution ： Some methods are common , I've rewritten this method in every subclass .

When to use ： There are some general methods .

How to solve ： Abstract these general algorithms .

Key code ： Implemented in abstract class , Other steps are implemented in subclasses .

Application example ：1、 When building a house , The foundation 、 Routing 、 The pipes are all the same , It was only later in the building that there were differences like closets and fences . 2、 In the journey to the west, the Bodhisattva decided 81 difficult , This is a top-level logical skeleton . 3、spring Chinese vs Hibernate Support for , Encapsulate some of the established methods , For example, opening a transaction 、 obtain Session、 close Session etc. , Programmers do not repeat code that is already well written , Just drop an entity and you can save it .

advantage ：1、 Encapsulate the invariant part , Extend the variable part . 2、 Extract public code , Easy to maintain . 3、 Behavior is controlled by the parent class , Subclass implementation .

shortcoming ： Each different implementation needs a subclass to implement it , Causes the number of classes to increase , Make the system bigger .

Use scenarios ：1、 There are methods common to many subclasses , And the logic is the same . 2、 Important 、 Complex methods , Consider as a template method .

matters needing attention ： To prevent malicious operation , General template methods add final key word .

Realization
We will create a... That defines the operation Game abstract class , among , The template method is set to final, So it won't be rewritten .Cricket and Football It's expanded Game The entity class , They override methods of abstract classes .

TemplatePatternDemo, Our demo class uses Game To demonstrate the use of template patterns .

 

step 1

Create an abstract class , Its template method is set to final.

Game.java

public abstract class Game {

    abstract void initialize();

    abstract void startPlay();

    abstract void endPlay();

    // Templates 
    public final void play() {
        // Initialize the game 
        initialize();

        // Start the game 
        startPlay();

        // End the game 
        endPlay();
    }

}

step 2

Create entity classes that extend the above classes .

Cricket.java

public class Cricket extends Game {

    @Override
    void endPlay() {
        System.out.println("Cricket Game Finished!");
    }

    @Override
    void initialize() {
        System.out.println("Cricket Game Initialized! Start playing.");
    }

    @Override
    void startPlay() {
        System.out.println("Cricket Game Started. Enjoy the game!");
    }
}

Football.java

public class Football extends Game {

    @Override
    void endPlay() {
        System.out.println("Football Game Finished!");
    }

    @Override
    void initialize() {
        System.out.println("Football Game Initialized! Start playing.");
    }

    @Override
    void startPlay() {
        System.out.println("Football Game Started. Enjoy the game!");
    }

}

step 3

Use  Game  Template method play() To demonstrate how games are defined .

TemplatePatternDemo.java

public class TemplatePatternDemo {

    public static void main(String[] args) {
        Game game = new Cricket();
        game.play();
        System.out.println();

        game = new Football();
        game.play();
    }

}

step 4

Verify output .

Cricket Game Initialized! Start playing.
Cricket Game Started. Enjoy the game!
Cricket Game Finished!

Football Game Initialized! Start playing.
Football Game Started. Enjoy the game!
Football Game Finished!