How can I find out with which version of Java the .class file was received?

Question

I am trying to figure 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 do not always have the JDK installed on the machine where I need to check. However, I do have access to a simple HEX editor ...

I tried to find documentation for this source from a certified source - all I could find was the following: http://fredericktang.wordpress.com/2007/09/28/java-class-file-version/
Although this blog post is beautifully written, it does not support official Java documentation.

Any clues?

Edit: Ignore - sorry for the error - I found the spec: here

Answer 1

The JVM specification is about as authoritative as you are going to get. Chapter 4 is what you need.

Answer 2

The documentation you refer to is almost a transcript (in plain English) of the specification of a JVM class file.

Some of the hitoric values ​​I support

 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 the observation of the Nile that 1.0 and 1.1 use the same Significant Minor Numbers ---

It is not possible to determine from the class header whether the class was compiled with Java version 1.0 or 1.1. However, there are a number of other methods that can help determine if a class has been compiled against 1.0 or 1.1.

First, if the class was compiled against 1.1, it could only include the 1.1 library class. When you find one of them in one of the classes, you can safely conclude that this is a class compiled against Java 1.1.

Note that at the beginning of a class, you can search for a constant pool to determine which classes a class file should have, so that all its external links are fully resolved.

It can be cumbersome to search for classes individually, fortunately, many packages have been added. 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 hand of the fence, many 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 a new restructuring of awt events.

 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. 

You can prove that Java code is version 1.1, but only in some cases (if the code uses new 1.1 features). As a rule, it is impossible to prove that the Java code was 1.0, but the lack of use of Java 1.1 functions and the intensive use of deprecated Java functions for classes intended for the Java 1.0 environment.

I do not know of any tags in the class that could distinguish between two (differences in line number tables, etc.), mainly because I did not have to dig through the classes 1.0 and 1.1 in the hexadecimal format of the editor.