How am I getting objects from a Set?

I started learning spring security few days ago. Found the same code in two tutorials and I'm not sure how is it doing it's job. I realize that's it is just plain java but I don't seem to understand it.

public Set<SimpleGrantedAuthority> getGrantedAuthority(){
        Set<SimpleGrantedAuthority> permissions = getPermissions().stream()
                .map(permission -> new SimpleGrantedAuthority(permission.getPermission()))
                .collect(Collectors.toSet());
        permissions.add(new SimpleGrantedAuthority("ROLE_" + this.name()));
        return permissions;
    } 

From my understanding of the code, with stream() I'm filling the Set with SimpleGrantedAuthority objects and that is fine, but what and how does this line work permissions.add(new SimpleGrantedAuthority("ROLE_" + this.name())); ?
Whole method should just return permissions for the given role but I am not sure how do i end up with just few right ones in the method return.

Method call:

 protected UserDetailsService userDetailsService() {
        UserDetails annaS = User.builder()
                .username("annasmith")
                .password(passwordEncoder.encode("password"))
                .authorities(STUDENT.getGrantedAuthority())
                .build();
}

Role enum:

public enum ApplicationUserRole {
    STUDENT(Sets.newHashSet()),
    ADMIN(Sets.newHashSet(COURSE_READ,COURSE_WRITE, STUDENT_WRITE, STUDENT_READ)),
    ADMINTRAINEE(Sets.newHashSet(COURSE_READ,STUDENT_READ));

    private final Set<ApplicationUserPermission> permissions;

    ApplicationUserRole(Set<ApplicationUserPermission> permissions) {
        this.permissions = permissions;
    }

    public Set<ApplicationUserPermission> getPermissions() {
        return permissions;
    }

    public Set<SimpleGrantedAuthority> getGrantedAuthority(){
        Set<SimpleGrantedAuthority> permissions = getPermissions().stream()
                .map(permission -> new SimpleGrantedAuthority(permission.getPermission()))
                .collect(Collectors.toSet());
        permissions.add(new SimpleGrantedAuthority("ROLE_" + this.name()));
        return permissions;
    } 
}

Permission enum:

public enum ApplicationUserPermission {
    STUDENT_READ("student:read"),
    STUDENT_WRITE("student:write"),
    COURSE_READ("course:read"),
    COURSE_WRITE("course:write");

    private final String permission;

    ApplicationUserPermission(String permission) {
        this.permission = permission;
    }

    public String getPermission() {
        return permission;
    }
}

Would appreciate if someone would explain me the line in detail, if there is anything to analyze in the first place.

In Spring Security, you can fill UserDetails authorities with ROLES and/or privilegies. The way you deal with this information is your choice, so what the quoted line is doing is just adding the ApplicationUserRole together the privilegies in the same place.

> For the framework, the difference is minimal – and it basically deals with these in exactly the same way.

> The Spring Security framework doesn't give any guidance in terms of how we should use the concept, so the choice is entirely implementation specific.

You could use that in Spring Security Configuration.

eg:

@Override
protected void configure(HttpSecurity http) throws Exception {
    // ...
    .antMatchers("/protectedbyrole").hasRole("STUDENT")
    .antMatchers("/protectedbyauthority").hasAuthority("student:read")
    // ...
}

Read more in https://www.baeldung.com/spring-security-granted-authority-vs-role.