# Tutorial - User Guide { #tutorial-user-guide }

This tutorial shows you how to use **FastAPI** with most of its features, step by step.

Each section gradually builds on the previous ones, but it's structured to separate topics, so that you can go directly to any specific one to solve your specific API needs.

It is also built to work as a future reference so you can come back and see exactly what you need.

## Run the code { #run-the-code }

        buf.append(Integer.toHexString(i >> 16 & 0xff));
        buf.append(Integer.toHexString(i >> 8 & 0xff));
        buf.append(Integer.toHexString(i & 0xff));
    }

    /**
     * Converts an underscore-separated string to camel case.
     * <p>
     * Usage example:
     * </p>
     *
     * <pre>
     * StringUtil.camelize("USER_ID")  = "UserId"
     * </pre>
     *
     * @param s

/**
 * Reads lines from `IdnaMappingTable.txt`.
 *
 * Comment lines are either blank or start with a `#` character. Lines may also end with a comment.
 * All comments are ignored.
 *
 * Regular lines contain fields separated by semicolons.
 *
 * The first element on each line is a single hex code point (like 0041) or a hex code point range
 * (like 0030..0039).
 *

{* ../../docs_src/query_params/tutorial001_py39.py hl[9] *}

The query is the set of key-value pairs that go after the `?` in a URL, separated by `&` characters.

For example, in the URL:

```
http://127.0.0.1:8000/items/?skip=0&limit=10
```

...the query parameters are:

* `skip`: with a value of `0`
* `limit`: with a value of `10`

 *
 * If output-file is provided, writes result to that file (avoids Windows file locking issues).
 * Otherwise, outputs to stdout.
 *
 * Outputs: Single line with space-separated quoted arguments (safe for batch scripts)
 */
public class JvmConfigParser {
    public static void main(String[] args) {
        if (args.length < 2 || args.length > 3) {

	// Bucket metrics are special, they always include the bucket label. These
	// metrics required a list of buckets to be passed to the loader, and the list
	// of buckets is not known until the request is made. So we keep a separate
	// map for bucket metrics and handle them specially.

	// Add the serverName and poolIndex labels to all non-cluster metrics.
	//
	// Also create metric group maps and set the cache.

    // This way we can catch discrepancies in modules easier. We should make all packages NullMarked eventually too, but this is a separate task.
    annotatedPackages.add("org.gradle")
}

dependencies {
    attributesSchema {
        attribute(NullawayAttributes.nullawayAttribute) {

     */
    @Nonnull
    Optional<String> option();

    /**
     * Returns the option followed by a string representation of the given path elements.
     * The path elements are separated by an option-specific or platform-specific separator.
     * If the given {@code paths} argument contains no element, then this method returns an empty string.
     *
     * <h4>Examples</h4>

     of this section 3.

3.2 When the Program is Distributed as Source Code:

  a) it must be made available under this Agreement, or if the
  Program (i) is combined with other material in a separate file or
  files made available under a Secondary License, and (ii) the initial
  Contributor attached to the Source Code the notice described in
  Exhibit A of this Agreement, then the Program may be made available

## Decision

Use "NullAway" in JSpecify mode to check for null-related errors in Java code.

Consider improper uses of `null` detected by NullAway a compilation error (not a warning, and not a separate CI job to test).

Do not suppress NullAway errors without a justification.
Prefer rearranging the code to avoid the error, unless there is a provable performance penalty or a significant loss of code readability.