Java Language Guide¶

linthis uses checkstyle for linting and clang-format for formatting Java code.

Supported File Extensions¶

.java

Required Tools¶

Linter: checkstyle¶

# macOS
brew install checkstyle

# Linux
sudo apt install checkstyle

# Windows
choco install checkstyle

# Or download JAR from https://checkstyle.org/

# Verify installation
checkstyle --version

Formatter: clang-format¶

# macOS
brew install clang-format

# Linux
sudo apt install clang-format

# Windows
choco install llvm

# Verify installation
clang-format --version

Place a .clang-format file in your project root to customize Java formatting style. linthis also checks .linthis/configs/java/.clang-format for plugin-provided configs.

Configuration¶

Basic Example¶

# .linthis/config.toml

[java]
max_complexity = 20
excludes = ["*Test.java", "target/**"]

Disable Specific Rules¶

[java.rules]
disable = [
    "MagicNumber",
    "LineLength"
]

Custom Rules¶

[[rules.custom]]
code = "java/no-system-out"
pattern = "System\\.(out|err)\\.print"
message = "Use logging framework instead of System.out"
severity = "warning"
suggestion = "Use SLF4J or Log4j"
languages = ["java"]

[[rules.custom]]
code = "java/no-wildcard-import"
pattern = "import\\s+[\\w.]+\\.\\*;"
message = "Avoid wildcard imports"
severity = "info"
languages = ["java"]

CLI Usage¶

# Check Java files only
linthis -c --lang java

# Format Java files only
linthis -f --lang java

Checkstyle Configuration¶

linthis uses Google's checkstyle configuration by default. To customize, create checkstyle.xml:

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
    "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
    "https://checkstyle.org/dtds/configuration_1_3.dtd">
<module name="Checker">
    <module name="TreeWalker">
        <module name="LineLength">
            <property name="max" value="120"/>
        </module>
    </module>
</module>

Common Issues¶

Checkstyle not found¶

Warning: No java linter available for java files
  Install: brew install checkstyle

Test files being checked¶

Add to excludes:

[java]
excludes = ["*Test.java", "*Tests.java", "src/test/**"]

Best Practices¶

Google style: Use Google's checkstyle configuration as a baseline
Line length: 120 characters is common for modern displays
Test exclusions: Consider different rules for test files
IDE integration: Configure your IDE to use the same checkstyle config