*/
    private int countUniqueBytes(byte[] data) {
        boolean[] seen = new boolean[256];
        int count = 0;

        for (byte b : data) {
            int index = b & 0xFF;
            if (!seen[index]) {
                seen[index] = true;
                count++;
            }
        }

        return count;
    }

# Advanced Dependencies { #advanced-dependencies }

## Parameterized dependencies { #parameterized-dependencies }

All the dependencies we have seen are a fixed function or class.

But there could be cases where you want to be able to set parameters on the dependency, without having to declare many different functions or classes.

Let's imagine that we want to have a dependency that checks if the query parameter `q` contains some fixed content.

* `ge`: `g`reater than or `e`qual
* `lt`: `l`ess `t`han
* `le`: `l`ess than or `e`qual

/// info

`Query`, `Path`, and other classes you will see later are subclasses of a common `Param` class.

All of them share the same parameters for additional validation and metadata you have seen.

///

/// note | Technical Details

When you import `Query`, `Path` and others from `fastapi`, they are actually functions.

# Extra Data Types { #extra-data-types }

Up to now, you have been using common data types, like:

* `int`
* `float`
* `str`
* `bool`

But you can also use more complex data types.

And you will still have the same features as seen up to now:

* Great editor support.
* Data conversion from incoming requests.
* Data conversion for response data.
* Data validation.
* Automatic annotation and documentation.

# Async Tests { #async-tests }

You have already seen how to test your **FastAPI** applications using the provided `TestClient`. Up to now, you have only seen how to write synchronous tests, without using `async` functions.

   * range [0, k) and ignore the remaining elements.
   */
  private final @Nullable T[] buffer;
  private int bufferSize;

  /**
   * The largest of the lowest k elements we've seen so far relative to this comparator. If
   * bufferSize ≥ k, then we can ignore any elements greater than this value.
   */
  private @Nullable T threshold;

	for _, c := range s {
		if c < 0x80 && c != 0x00 {
			b = append(b, byte(c))
		}
	}
	return string(b)
}

type parser struct {
	err error // Last error seen
}

type formatter struct {
	err error // Last error seen
}

// parseString parses bytes as a NUL-terminated C-style string.
// If a NUL byte is not found then the whole slice is returned as a string.
func (*parser) parseString(b []byte) string {

# Body - Multiple Parameters { #body-multiple-parameters }

Now that we have seen how to use `Path` and `Query`, let's see more advanced uses of request body declarations.

## Mix `Path`, `Query` and body parameters { #mix-path-query-and-body-parameters }

First, of course, you can mix `Path`, `Query` and request body parameter declarations freely and **FastAPI** will know what to do.

# Custom Response - HTML, Stream, File, others { #custom-response-html-stream-file-others }

By default, **FastAPI** will return the responses using `JSONResponse`.

You can override it by returning a `Response` directly as seen in [Return a Response directly](response-directly.md){.internal-link target=_blank}.

{* ../../docs_src/query_params/tutorial004_py310.py hl[6,8] *}

## Required query parameters { #required-query-parameters }

When you declare a default value for non-path parameters (for now, we have only seen query parameters), then it is not required.

If you don't want to add a specific value but just make it optional, set the default as `None`.