Java Source Code Style Guide

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Quick Example:

// Most Javadoc left out for brevity!
import java.io.*;
import java.util.*;

import com.jthreadkit.*;

public class QuickExample extends Object implements Comparable, Serializable {
    public static final int NO_ALIGNMENT = 1;
    private int count;
    private int numStudents;
    private String[] name;

    public QuickExample(
                int param,
                String stuff,
                double otherThings,
                boolean useShortcut
            ) throws IllegalArgumentException {

        this.count = param + 25;
        // ...
    }

    public QuickExample(int param) throws IllegalArgumentException {
        this(param, null, 0.0, true);
    }

    public void someMethod() {
        if ( boolExprA ) {
            // ...
        } else if ( boolExprB ) {
            // ...
        } else {
            // ...
        }

        for ( int i = 0; i < str.length; i++ ) {
            // ...
        }

        while ( blah ) {
            // ...
        }

        synchronized ( this ) {
            // ...
        }

        try {
            // ...
        } catch ( XYZException x ) {
            x.printStackTrace();
        } finally {
            // ...
        }

        switch ( expr ) {
            case 'A':
            case 'X':
                // ...
                break;

            default:
                break;
        }

        button.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    // ...
                }
            });
    }

    /**
     * Calculates the complicated thing and returns the result
     * of the stuff...
     *
     * @return a negative number indicating...
     */
    public int process() {
        // ...
    }

    public static void main(String[] args) {
        // ...
    }
}

Items to take note of:

• The tabstop is set to 4. Spaces are vastly preferred over tabs to indent code as it then looks correct everywhere.
• No lines are longer than 80 characters.
• One blank line between method declarations.
• Open curly braces '{' are at the end of a line, and the corresponding closing brace '}' is directly under the first character of the line that opened the brace. Compound structures close the brace and then open a new one on the same line, ex: "} else {". All code within the curly brace block is indented one level. Curly braces are always used even for single statement blocks.
• Class names begin with a capital letter and use mixed case. Underscores are prohibited and digits are avoided.
• Method names begin with a lower-case letter and use mixed case. Underscores are prohibited and digits are avoided.
• Member variables, passed parameters, and local variable names begin with a lower-case letter and use mixed case. Underscores are prohibited and digits are avoided. No special prefixes are used to differentiate member variables, parameters, or local variables.
• Constants like NO_ALIGNMENT are in all capitals with underscores breaking up words.
• Within a source file, member variables are listed first, then constructors, then methods, then nested classes and nested interfaces.
• If there is a main method, it is the last method.
• Arrays types are declared with the square brackets appended to the array component type, ex: "double[] value".
• Only one top-level class per .java file (no package-scope classes). Inner and Nested classes and interfaces are permitted.
• The import's are done using * whenever possible (for example: import java.util.*;).

Other Java style guides:

Sun Microsystems' Source Code Style Conventions (at java.sun.com)

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