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austere sparrow
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what is <?>

pine roostBOT
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<@&987246924425994290> please have a look, thanks.

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TJ-Bot
In Java what does <?> symbolize

The <?> symbol in Java represents a wildcard in generics. It is used when the specific type of a generic parameter is unknown or irrelevant.

When declaring a generic class or method, you can use the <?> wildcard to allow any type to be passed as an argument. This is useful when you want to create a more flexible and reusable code that can work with different types without specifying them explicitly.

For example, if you have a List<?> variable, it means that the list can contain any type of objects. You can still add elements to the list, but you cannot retrieve them without casting to a specific type.

The <?> symbol is often used in conjunction with bounded wildcards (<? extends T> or <? super T>) to further restrict the types that can be used as arguments in generics.

Overall, the <?> wildcard allows for more generic and flexible programming in Java by providing a way to work with unknown types in generics.

- AI generated response
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TJ-Bot
What is a generic in java

In Java, generics allow you to create classes, interfaces, and methods that operate on specified types rather than specific ones. This allows you to write more flexible and reusable code by allowing you to define classes and methods without committing to a specific data type.

Generics are defined using angle brackets <> and can be applied to classes, interfaces, methods, and even variables. When you define a generic class or method, you can specify the type or types it will work with when you instantiate an object or call the method.

For example, if you have a List interface that you want to work with various types of data, you can define it as List<T>, where T is a placeholder for the actual type. Then when you create an instance of List, you can specify the type it will work with such as List<String> or List<Integer>.

Using generics helps improve type safety by catching errors at compile time rather than runtime. It also reduces the need for casting objects and makes your code more readable and maintainable.

Overall, generics in Java provide a powerful tool for creating flexible and reusable code that can work with different data types while ensuring type safety.

- AI generated response
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TJ-Bot
Can you give an example of a generic with <?> being used

Sure! In Java, the <?> symbol is known as an unbounded wildcard and is used to represent an unknown type. It can be used in a variety of ways, such as in generic methods or classes.

Here is an example of a generic method using <?>:

public class GenericExample {

    public static void printList(List<?> list) {
        for (Object element : list) {
            System.out.println(element);
        }
    }

    public static void main(String[] args) {
        List<Integer> integerList = Arrays.asList(1, 2, 3);
        List<String> stringList = Arrays.asList("Hello", "World");

        printList(integerList);
        printList(stringList);
    }
}

In this example, the printList method takes a List with an unbounded wildcard <?>. This means it can accept any type of List, whether it be a List of integers, strings, or any other object. The method then iterates through the elements in the list and prints each one.

By using <?>, we are creating a more flexible and reusable method that can work with different types of Lists without specifying a specific type.

- AI generated response
wintry root
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its called wildcards

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u should first get familiar with normal generics

austere sparrow
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i had a hard time googling it because for some reason it wouldent parse it, it only parsed it as "?" 😄

wintry root
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once thats done, u can read about wildcards

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yeah definitely 😄

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its similar to List<T> but u dont care for the type at all

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so just List<?>

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but bc u dont even give the type a name (like T), u cant even use it at all

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like, u cant get anything out of that list and u cant put anything into it

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if u have to do any of that u would either do
? extends Foo
? super Foo
or just a normal generic T

austere sparrow
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thanks

austere sparrow
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    public ResponseEntity<?> registerUser(@Valid @RequestBody SignupRequest signUpRequest) {
        if (userRepository.existsByUsername(signUpRequest.getUsername())) { return ResponseEntity.badRequest().body(new MessageResponse("Error: Username is already taken!")); }
        if (userRepository.existsByEmail(signUpRequest.getEmail())) { return ResponseEntity.badRequest().body(new MessageResponse("Error: Email is already in use!")); }

        User user = new User(signUpRequest.getUsername(), signUpRequest.getEmail(), encoder.encode(signUpRequest.getPassword()));
        Set<String> strRoles = signUpRequest.getRole();
        Set<Role> roles = new HashSet<>();

        if (strRoles == null) { Role userRole = roleRepository.findByName(ERole.ROLE_USER).orElseThrow(() -> new RuntimeException("Error: Role is not found.")); roles.add(userRole);
        } else {
            strRoles.forEach(role -> {
                switch (role) {
                    case "admin": Role adminRole = roleRepository.findByName(ERole.ROLE_ADMIN).orElseThrow(() ->      new RuntimeException("Error: Role is not found.")); roles.add(adminRole); break;
                    case "mod":   Role modRole   = roleRepository.findByName(ERole.ROLE_MODERATOR).orElseThrow(() ->  new RuntimeException("Error: Role is not found.")); roles.add(modRole); break;
                    default:      Role userRole  = roleRepository.findByName(ERole.ROLE_USER).orElseThrow(() ->       new RuntimeException("Error: Role is not found.")); roles.add(userRole);
                }
            });
        }

        user.setRoles(roles);
        userRepository.save(user);
        return ResponseEntity.ok(new MessageResponse("User registered successfully!"));
    }

So whats happening in this function is that it returns a ResponseEntity of any type? Thats why <?> is being used? I ask because i dont see the ? being used anywhere else in the code besides the return type

pine roostBOT
austere sparrow
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@wintry root

wintry root
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it will be a very concrete type but its left unspecified for whoever would call that method and want to use the returned value

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since this is a spring controller though, u likely wont call this method normally and use the returned value

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id suggest studying these topics outside of special use cases and systems like spring first

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then it makes more sense

austere sparrow
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Okay, thanks for clearing that up