Title: Java class file
Content:  A Java class file is a file (with the .class filename extension) containing Java bytecode that can be executed on the Java Virtual Machine (JVM). A Java class file is usually produced by a Java compiler from Java programming language source files (.java files) containing Java classes (alternatively, other JVM languages can also be used to create class files). If a source file has more than one class, each class is compiled into a separate class file. JVMs are available for many platforms, and a class file compiled on one platform will execute on a JVM of another platform. This makes Java applications platform-independent.
Title: Java (programming language)
Content:  The traditional Hello world program can be written in Java as: All source files must be named after the public class they contain, appending the suffix, for example,. It must first be compiled into bytecode, using a Java compiler, producing a file with the  suffix (, in this case). Only then can it be executed or launched. The Java source file may only contain one public class, but it can contain multiple classes with a non-public access modifier and any number of public inner classes. When the source file contains multiple classes, it is necessary to make one class (introduced by the  keyword) public (preceded by the   keyword) and name 
Title: Archive file
Content:  Filename extensions used to distinguish different types of archives include zip, rar, 7z, and tar, the first of which is the most widely implemented. Java also introduced a whole family of archive extensions such as jar and war (j is for Java and w is for web). They are used to exchange entire byte-code deployment. Sometimes they are also used to exchange source code and other text, HTML and XML files. By default they are all compressed.
Title: Comparison of C Sharp and Java
Content:  add a method to a type (e.g., allowing foo.bar where bar can be an imported extension method working on the type of foo ). The Sun Microsystems Java compiler requires that a source file name must match the only public class inside it, while C# allows multiple public classes in the same file, and puts no restrictions on the file name. C# 2.0 and later allows splitting a class definition into several files by using the partial keyword in the source code. In Java, a public class will always be in its own source file. In C#, source code files and logical units separation are not tightly related.
Title: JAR (file format)
Content:  A JAR (Java ARchive) is a package file format typically used to aggregate many Java class files and associated metadata and resources (text, images, etc.) into one file for distribution. JAR files are archive files that include a Java-specific manifest file. They are built on the ZIP format and typically have a  file extension.
Title: Apache Axis
Content:  JWS files contain Java class source code that should be exposed as Web service. The main difference between an ordinary java file and jws file is the file extension. Another difference is that jws files are deployed as source code and not compiled class files. The following example will expose methods add and subtract of class Calculator.
Title: JPEG
Content:  The most common filename extensions for files employing JPEG compression are .jpg and .jpeg, though .jpe, .jfif and .jif are also used. It is also possible for JPEG data to be embedded in other file types – TIFF encoded files often embed a JPEG image as a thumbnail of the main image; and MP3 files can contain a JPEG of cover art in the ID3v2 tag.
Title: Java (programming language)
Content:  source file with that public class name. A class that is not declared public may be stored in any  file. The compiler will generate a class file for each class defined in the source file. The name of the class file is the name of the class, with .class appended. For class file generation, anonymous classes are treated as if their name were the concatenation of the name of their enclosing class, a $, and an integer. The keyword  denotes that a method can be called from code in other classes, or that a class may be used by classes outside the class hierarchy. The class hierarchy is related to 
Title: Magic number (programming)
Content: Examples ; Compiled Java class files (bytecode) and Mach-O binaries start with hex . When compressed with Pack200 the bytes are changed to. ; GIF image files have the ASCII code for "GIF89a" or "GIF87a" ; JPEG image files begin with    and end with    . JPEG/JFIF files contain the ASCII code for "JFIF"  as a null terminated string. JPEG/Exif files contain the  ASCII code for "Exif"  also as a null terminated string, followed by more metadata about the file. ; PNG image files begin with an 8-byte signature which identifies the file as a PNG file and allows detection of 
Title: Filename extension
Content:  A filename extension, file extension or file type is an identifier specified as a suffix to the name of a computer file (.txt, .docx, .ppt, etc.). The extension indicates a characteristic of the file contents or its intended use. A filename extension is typically delimited from the filename with a full stop (period), but in some systems it is separated with spaces. Some file systems implement filename extensions as a feature of the file system itself and may limit the length and format of the extension, while others treat filename extensions as part of the filename without special distinction.

Question: what is the filename extension used for all java source files?
Answer: .java.