How can I know with which Java version a .class file is got was compiled?
I’m trying to find out how I can determine the version of a .class file by looking at its binary data. I know that using javap will tell me the version — but unfortunately I don’t always have a JDK installed on the machine where I need to check. I do however have access to a plain old HEX editor . I tried finding documentation on this from a certified source — all I was able to come up was with this: http://fredericktang.wordpress.com/2007/09/28/java-class-file-version/
Although this blog post is very nicely written — it is not really backed up by official Java documentation. Any hint? Edit: Never mind — sorry to bug — I found the spec: here
@McDowell — I don’t see it as a duplicate. Programatically getting information is not the same as doing it by viewing a file with a HEX editor.
2 Answers 2
The documentation you referenced is practically a word-for-word transcription (into easier English) of the JVM class file specification.
Some of the hitoric values I keep handy
Major Major(hex) Minor Java platform version 45 2d 3 1.0 45 2d 3 1.1 46 2e 0 1.2 47 2f 0 1.3 48 30 0 1.4 49 31 0 1.5 50 32 0 1.6 — Edited in response to Neil’s observation that 1.0 and 1.1 use the same Major Minor numbers —
From the class header, one cannot determine whether the class was compiled against a 1.0 or 1.1 version of Java. That said, there are a number of other techniques that can help determine if a class was compiled against 1.0 or 1.1.
First, if the class was compiled against 1.1 it might have included a 1.1 only library class. Once you find one of these in one of the classes, you can safely conclude that it’s a class compiled against Java 1.1.
Note that one may search the constant pool at the beginning of the class to determine which classes the class file will need to have all of its external references fully resolved.
It can be cumbersome to search for classes individually, fortunately a lot of packages were added too. The following packages are specific to Java 1.1, that is they were not included in Java 1.0
+ java.awt.datatransfer + java.awt.event + java.beans + java.lang.reflect + java.math + java.rmi.dgc + java.rmi + java.rmi.registry + java.rmi.server + java.security.acl + java.security + java.security.interfaces + java.sql + java.text + java.util.zip On the other side of the fence, lots of calls to the following methods suggest (but are not actual proof) that the code was written against Java 1.0, as they were deprecated in Java 1.1 due to the new awt event restructuring.
Deprecated Classes java.io.LineNumberInputStream: LineNumberInputStream is deprecated. java.io.StringBufferInputStream: StringBufferInputStream is deprecated. Deprecated Methods java.awt.BorderLayout: addLayoutComponent() is deprecated. java.awt.CardLayout: addLayoutComponent() is deprecated. java.awt.CheckboxGroup: getCurrent() is deprecated. java.awt.CheckboxGroup: setCurrent() is deprecated. java.awt.Choice: countItems() is deprecated. java.awt.Component: getPeer() is deprecated. java.awt.Component: enable() is deprecated. java.awt.Component: enable() is deprecated. java.awt.Component: disable() is deprecated. java.awt.Component: show() is deprecated. java.awt.Component: show() is deprecated. java.awt.Component: hide() is deprecated. java.awt.Component: location() is deprecated. java.awt.Component: move() is deprecated. java.awt.Component: size() is deprecated. java.awt.Component: resize() is deprecated. java.awt.Component: resize() is deprecated. java.awt.Component: bounds() is deprecated. java.awt.Component: reshape() is deprecated. java.awt.Component: preferredSize() is deprecated. java.awt.Component: minimumSize() is deprecated. java.awt.Component: layout() is deprecated. java.awt.Component: inside() is deprecated. java.awt.Component: locate() is deprecated. java.awt.Component: deliverEvent() is deprecated. java.awt.Component: postEvent() is deprecated. java.awt.Component: handleEvent() is deprecated. java.awt.Component: mouseDown() is deprecated. java.awt.Component: mouseDrag() is deprecated. java.awt.Component: mouseUp() is deprecated. java.awt.Component: mouseMove() is deprecated. java.awt.Component: mouseEnter() is deprecated. java.awt.Component: mouseExit() is deprecated. java.awt.Component: keyDown() is deprecated. java.awt.Component: keyUp() is deprecated. java.awt.Component: action() is deprecated. java.awt.Component: gotFocus() is deprecated. java.awt.Component: lostFocus() is deprecated. java.awt.Component: nextFocus() is deprecated. java.awt.Container: countComponents() is deprecated. java.awt.Container: insets() is deprecated. java.awt.Container: layout() is deprecated. java.awt.Container: preferredSize() is deprecated. java.awt.Container: minimumSize() is deprecated. java.awt.Container: deliverEvent() is deprecated. java.awt.Container: locate() is deprecated. java.awt.FontMetrics: getMaxDecent() is deprecated. java.awt.Frame: setCursor() is deprecated. java.awt.Frame: getCursorType() is deprecated. java.awt.Graphics: getClipRect() is deprecated. java.awt.List: countItems() is deprecated. java.awt.List: clear() is deprecated. java.awt.List: isSelected() is deprecated. java.awt.List: allowsMultipleSelections() is deprecated. java.awt.List: setMultipleSelections() is deprecated. java.awt.List: preferredSize() is deprecated. java.awt.List: preferredSize() is deprecated. java.awt.List: minimumSize() is deprecated. java.awt.List: minimumSize() is deprecated. java.awt.List: delItems() is deprecated. java.awt.Menu: countItems() is deprecated. java.awt.MenuBar: countMenus() is deprecated. java.awt.MenuComponent: getPeer() is deprecated. java.awt.MenuComponent: postEvent() is deprecated. java.awt.MenuContainer: postEvent() is deprecated. java.awt.MenuItem: enable() is deprecated. java.awt.MenuItem: enable() is deprecated. java.awt.MenuItem: disable() is deprecated. java.awt.Polygon: getBoundingBox() is deprecated. java.awt.Polygon: inside() is deprecated. java.awt.Rectangle: reshape() is deprecated. java.awt.Rectangle: move() is deprecated. java.awt.Rectangle: resize() is deprecated. java.awt.Rectangle: inside() is deprecated. java.awt.ScrollPane: layout() is deprecated. java.awt.Scrollbar: getVisible() is deprecated. java.awt.Scrollbar: setLineIncrement() is deprecated. java.awt.Scrollbar: getLineIncrement() is deprecated. java.awt.Scrollbar: setPageIncrement() is deprecated. java.awt.Scrollbar: getPageIncrement() is deprecated. java.awt.TextArea: insertText() is deprecated. java.awt.TextArea: appendText() is deprecated. java.awt.TextArea: replaceText() is deprecated. java.awt.TextArea: preferredSize() is deprecated. java.awt.TextArea: preferredSize() is deprecated. java.awt.TextArea: minimumSize() is deprecated. java.awt.TextArea: minimumSize() is deprecated. java.awt.TextField: setEchoCharacter() is deprecated. java.awt.TextField: preferredSize() is deprecated. java.awt.TextField: preferredSize() is deprecated. java.awt.TextField: minimumSize() is deprecated. java.awt.TextField: minimumSize() is deprecated. java.awt.Window: postEvent() is deprecated. java.io.ByteArrayOutputStream: toString() is deprecated. java.io.DataInputStream: readLine() is deprecated. java.io.PrintStream: PrintStream() is deprecated. java.io.PrintStream: PrintStream() is deprecated. java.io.StreamTokenizer: StreamTokenizer() is deprecated. java.lang.Character: isJavaLetter() is deprecated. java.lang.Character: isJavaLetterOrDigit() is deprecated. java.lang.Character: isSpace() is deprecated. java.lang.ClassLoader: defineClass() is deprecated. java.lang.Runtime: getLocalizedInputStream() is deprecated. java.lang.Runtime: getLocalizedOutputStream() is deprecated. java.lang.String: String() is deprecated. java.lang.String: String() is deprecated. java.lang.String: getBytes() is deprecated. java.lang.System: getenv() is deprecated. java.net.Socket: Socket() is deprecated. java.net.Socket: Socket() is deprecated. java.util.Date: Date() is deprecated. java.util.Date: Date() is deprecated. java.util.Date: Date() is deprecated. java.util.Date: Date() is deprecated. java.util.Date: UTC() is deprecated. java.util.Date: parse() is deprecated. java.util.Date: getYear() is deprecated. java.util.Date: setYear() is deprecated. java.util.Date: getMonth() is deprecated. java.util.Date: setMonth() is deprecated. java.util.Date: getDate() is deprecated. java.util.Date: setDate() is deprecated. java.util.Date: getDay() is deprecated. java.util.Date: getHours() is deprecated. java.util.Date: setHours() is deprecated. java.util.Date: getMinutes() is deprecated. java.util.Date: setMinutes() is deprecated. java.util.Date: getSeconds() is deprecated. java.util.Date: setSeconds() is deprecated. java.util.Date: toLocaleString() is deprecated. java.util.Date: toGMTString() is deprecated. java.util.Date: getTimezoneOffset() is deprecated. It is possible to prove that Java code is version 1.1, but only in some cases (if the code uses newly added 1.1 features). It is generally impossible to prove that Java code was 1.0, but the lack of any use of Java 1.1 features, and heavy use of Java’s deprecated features hints to classes targeted for the Java 1.0 environment.
I am unaware of any in-class tagging which might be able to differentiate the two (differences in line number tables, etc.), mostly because I haven’t had the need to dig through 1.0 and 1.1 classes in a hex editor.
List of Java class file format major version numbers?
Where does this list come from? Is there a specific reference for this? Preferably something that shows minor versions too?
7 Answers 7
These come from the class version. If you try to load something compiled for java 6 in a java 5 runtime you’ll get the error, incompatible class version, got 50, expected 49. Or something like that.
See here in byte offset 7 for more info.
Additional info can also be found here.
Is there a way to echo the major version number (class version) directly from javac, without using an existing class like, javap -verbose MyClass ?
Official source for major version number:
The latest published version of the JVM spec can be found here.
I found a list of Java class file versions on the Wikipedia page that describes the class file format:
Under byte offset 6 & 7, the versions are listed with which Java VM they correspond to.
If you have a class file at build/com/foo/Hello.class , you can check what java version it is compiled at using the command:
$ javap -v build/classes/com/example/Book.class | grep major major version: 57 According to the table in the OP, major version 57 means the class file was compiled to JDK 13 bytecode level
(Really an extended comment than an answer ..)
The question was regarding «where does the list of versions come from».
That was answered in this response, which references the JAVA SE Specification on: «The class File Format». Seems that’s pretty authoritative (it’s also referenced in the Wiki for the byte 6 (major version) values) and should be the accepted answer.
Several answers seem to focus on how to determine the value using javap or not using it. Those should be separate questions. Nevertheless, a non- javap means of finding the version is unix command file . file reads the magic , which is specified in the ClassFile structure.
ie: file myClass.class , or more elegantly, file -b myClass.class | awk -F’,’ »
$ find * -name "*.class" -exec file -b <> \; | awk -F',' '' | sort -u version 45.3 version 50.0 (Java 1.6) version 52.0 (Java 1.8)