pc-di

Programming Concepts - Dependency Injection

There are three version releases

• v1.0.0: Dependency Injection using Google Guice
• v2.0.0: Dependency Injection using spring annotations
• v3.0.0: Dependency Injection using spring xml

For this example project taken a well nown Example.

There is a Laptop class and there are two dependencies

Method Injection

Using the setter injection, we can set the dependencies after initialize the object

Method Injection

Using method injection, we can invoke the methods automatically without invoking them. We can do it by using @Autowired annotation.

@Autowired
public void displayProcessorReport(){
    System.out.println("----Processor------");
    System.out.println("storage:"+this.processor.getBrand());
    System.out.println("brand  :"+this.processor.getCoreCount());
    System.out.println("speed  :"+this.processor.getClockSpeed());
}

No need to invoke the method

public static void main(String[] args) {
    new AnnotationConfigApplicationContext(Settings.class).getBean(Laptop.class);
}

But if there are many methods, we need to consider excecuting order as well. We can use following annotations to fix that

@PostConstruct
@DependsOn()

We can write the Laptop.java class as follows.

@Component
public class Laptop {
    @Autowired
    private Ram ram;
    @Autowired
    public Processor processor;

    @Autowired
    @PostConstruct
    @DependsOn({"ram"})
    public void displayRamReport(){
        System.out.println("----RAM------");
        System.out.println("storage:"+this.ram.getStorage());
        System.out.println("brand  :"+this.ram.getBrand());
        System.out.println("speed  :"+this.ram.getClockSpeed());
    }

    @Autowired
    @PostConstruct
    @DependsOn({"processor", "displayRamReport"})
    public void displayProcessorReport(){
        System.out.println("----Processor------");
        System.out.println("storage:"+this.processor.getBrand());
        System.out.println("brand  :"+this.processor.getCoreCount());
        System.out.println("speed  :"+this.processor.getClockSpeed());
    }
}