Code Style

We follow Google’s Java Style Guidelines with a few additions and modifications, which are described herein.

Tip

You can use our code styles for Eclipse or IntelliJ IDEA to let your IDE format the code correctly for you. See Preparing for Development for more information.

• Line endings
  • Use Unix line endings when committing (\n)
    • Windows users of Git can do git config --global core.autocrlf true to let Git convert them automatically
• Column width
  • 80 for Javadocs
  • 150 for code
  • Feel free to wrap when it will help with readability
• Indentation
  • Use 4 spaces for indentations, do not use 2 spaces
• Vertical whitespace
  • Place a blank line before the first member of a class, interface, enum, etc. (i.e. after class Example {) as well as after the last member
• File headers
  • File headers must contain the license headers for the project. Use the updateLicenses Gradle task to add them automatically
• Imports
  • Imports must be grouped in the following order, where each group is separated by an empty line
    • Static imports
    • All other imports
    • java imports
    • javax imports
  • This differs from Google’s style in that imports are not grouped by top-level package, they are all grouped as one.
• Exceptions
  • For exceptions that are to be ignored, name the exception variable ignored
• Field accesses
  • Qualify all field accesses with this
• Javadocs
  • Do not use @author
  • Wrap additional paragraphs in <p> and </p>
  • Capitalize the first letter in the descriptions within each “at clause”, i.e. @param name Player to affect, no full stops
• End of file
  • Each file should end with an empty line

Code Conventions

• Use Optionals instead of returning null in the API
• Method parameters accepting null must be annotated with @Nullable (from javax.*), all methods and parameters are @Nonnull by default.
• Use Google Preconditions for null- and argument checking.

The Gist

While we urge that you read Google’s Java conventions particularly, the two are fairly long documents. To get you started quickly, here is an example of properly formatted code:

/*
* This file is part of Sponge, licensed under the MIT License (MIT).
*
* Copyright (c) SpongePowered <https://www.spongepowered.org>
* Copyright (c) contributors
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package org.spongepowered.example;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.inject.Inject;
import org.slf4j.Logger;

import java.util.Optional;
import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;

import javax.annotation.Nullable;

/**
* An example class which generates a new ID based on a specified base string
* and a randomly generated integer.
*
* <p>There is a chance the integer purposely fails to generate, in which case
* you can choose to provide a backup integer.</p>
*/
public class Example {

    private static final long SEED = 4815162342L;

    @Inject
    private Logger logger;

    private final String base;
    private final Random random;

    public Example(String base) {
        checkNotNull(base, "The specified base string cannot be null!");
        this.base = base;
        this.random = ThreadLocalRandom.current();
        this.random.setSeed(SEED);
    }

    /**
    * Generates and returns an ID using the base string specified on creation
    * or the alternative string if specified as well as a randomly generated
    * integer, which purposely fails to generate around 50% of the time.
    *
    * <p>A {@link ThreadLocalRandom} is used to check if the integer should
    * be generated and generates the integer itself if so.</p>
    *
    * @param alternate An alternate base string which will be used if not null
    * @return The generated ID, if available
    */
    public Optional<String> generateId(@Nullable String alternate) {
        if (this.random.nextBoolean()) {
            return Optional.of(alternate == null ? this.base : alternate + " - " + this.random.nextInt());
        }

        return Optional.empty();
    }

    /**
    * Generates and returns an ID using the base string specified on creation,
    * using a randomly generated integer if it was generated successfully, or
    * using the backup integer you specify.
    *
    * <p>A {@link ThreadLocalRandom} is used to check if the integer should
    * be generated and generates the integer itself if so. If it was not
    * generated, that is when your backup integer will be used.</p>
    *
    * @param backup A backup integer to use to create the ID with
    * @return The generated ID using the generated integer or the ID created
    *     using the backup integer specified
    */
    public String generateId(int backup) {
        return generateId(null).orElse(this.base + " - " + backup);
    }

}