Spring : @Autowired annotation - where to view the actual changes?

Question

Based on the example being followed here : https://dzone.com/articles/autowiring-in-spring

import org.springframework.stereotype.Component;

@Component
public class Department {
    private String deptName;
    public String getDeptName() {
        return deptName;
    }
    public void setDeptName(String deptName) {
        this.deptName = deptName;
    }
}

The @Autowired annotation is placed on the Department.

import org.springframework.beans.factory.annotation.Autowired;

public class Employee {
    private int eid;
    private String ename;
    @Autowired
    private Department department; //<----------------------
    public int getEid() {
        return eid;
    }
    public void setEid(int eid) {
        this.eid = eid;
    }
    public String getEname() {
        return ename;
    }
    public void setEname(String ename) {
        this.ename = ename;
    }
    public Department getDepartment() {
        return department;
    }
    public void setDepartment(Department department) {
        this.department = department;
    }
    public void showEmployeeDetails(){
        System.out.println("Employee Id : " + eid);
        System.out.println("Employee Name : " + ename);
        System.out.println("Department : " + department.getDeptName());
    }
}

This runs the program.

public class RunThis {
    public static void main(String[] args) 
    {
        System.out.println("Hello World");
        Employee emp = new Employee();
        emp.showEmployeeDetails();
    }
}

Running the program results in a NULL exception which is expected, but per the provided URL, it reads :

@Autowired on Properties
In the below example, when the annotation is directly used on properties, Spring looks for and injects Department when Employee is created. 

As a result, I interpreted to mean that the Department object would implicitly be instantiated behind the scenes at the time the Employee object is instantiated, but apparently that is wrong.

1 - How can this sample be modified to view the actual benefits of the @Autowired annotation?

Many other examples discuss the @Autowired annotation affecting what is written to some XML file in my project.

I searched my project for all files and don't see any reference toward the object (Department) other than Employee and Department.

2 - Where is the XML file located that one can view the changes affected by the use of the @Autowired annotation?

Answer 1

I think you're missing the bigger picture. You annotate classes so that they're managed by Spring. In order to use Spring you'll have to adapt your main.

@SpringBootApplication
public class RunThis {
    public static void main(String[] args) 
    {
        SpringApplication.run(RunThis.class, args);
        System.out.println("Hello World");
        Employee emp = new Employee();
        emp.showEmployeeDetails();
    }
}

Now our project is managed in Spring but our Employee isn't as we make this. We should let Spring handle this by creating a bean for our employee and fetching that bean. The creation of beans we do in classes annotated in @Configuration or via a ComponentScan.

Also all your changes when it comes to annotating won't be vissible in any .xml file.