java.lang.UnsupportedClassVersionError is a quite common error after NoClassDefFoundError or ClassNotFoundException they all seems to related to class files but they all are different and there cause and resolution are different. In this java tutorial we will see what is UnsupportedClassVersionError in Java? Why UnsupportedClassVersionError comes in Java? What is class file format and version numbers associated with it and finally how to resolve UnsupportedClassVersionError in Java.
This article is in continuation of debugging tutorials like How to remote debug Java program in Eclipse and 10 Java debugging tips in Eclipse. If you have not read those article you may find them useful.
How to resolve UnsupportedClassVersionError in Java
What is UnSupportedClassVersionError in Java?
Java.lang.UnsupportedClassVersionError is a subclass of java.lang.ClassFormatError. This is a kind of linking error which occurs during linking phase accordingly java.lang.ClassFormatError has also derived from java.lang.LinkageError. As the name suggests "UnSupportedClassVersionError" so it’s related to unsupported class version, now questions comes what is class version in Java? Well every source file is compiled into class file and each class file has two versions associated with it, major version and minor version. Version of class file is represented as major_version.minor_version. This version is used to determine format of class file in Java.According to Java Virtual Machine specification, “A JVM implementation can support a class file format of version v if and only if v lies in some contiguous range Mi.0 v Mj.m. Only Sun can specify what range of versions a JVM implementation conforming to a certain release level of the Java platform may support.” For example: JDK 1.2 supports class file formats from version 45.0 to version 46.0 inclusive. So if a class file has version 48.0 it means that major version of class file is "48" and minor version is "0", which tells us that JDK 1.4 has been used to compile and generate that class file.
When UnSupportedClassVersionError in Java comes:
So now we got the theory behind class file format and major and minor version of class file in Java. Now a million dollar question is when UnSupportedClassVersionError in Java does occur? precise answer of this is "When JVM tries to load a class and found that class file version is not supported it throws UnSupportedClassVersionError and it generally occurs if a higher JDK version is used to compile the source file and a lower JDK version is used to run the program. for example if you compile your java source file in JDK 1.5 and you will try to run it on JDK 1.4 you will get error "java.lang.UnsupportedClassVersionError: Bad version number in .class file [at java.lang.ClassLoader.defineClass1(Native Method)]".
But its important to note is that vice-versa is not true "you can compile your program in J2SE 1.4 and run on J2SE 1.5 and you will not get any UnSupportedClassVersionError". When a higher JDK is used for compilation it creates class file with higher version and when a lower JDK is used to run the program it found that higher version of class file not supported at JVM level and results in java.lang.UnsupportedClassVersionError.
How to fix UnSupportedClassVersionError
Now we know the root cause of UnSupportedClassVersionError that we are using a lower JVM for running the program. But major problem is that stack trace of UnSupportedClassVersionError will not tell you for which class it’s coming. So if you are using multiple third party jars in your application you find that it comes at a particular part when JVM tries to load a class from a particular jar. anyway we all know that latest version of JDK is 1.6 so maximum version of class file could be generated by JDK 6, so by using JDK 6 we can solve UnSupportedClassVersionError, but many times its not easy to just move to higher JDK version. So I would suggest:
1) Find out due to which jar or class file this UnSupportedClassVersionError is coming?
2) Try to compile source code of that jar with the JDK version you are using to run your program, if source is available.
3) If you don't have source try to find the compatible version of that library.
4) Increase the JRE version you are using to run your program.
You can go by any approach to resolve UnSupportedClassVersionError based upon your need. Generally a higher JVM version is ok and does not cause any problem unless the class file format is quite old and no more supported by Sun in higher JVMs. The best way to deal with UnSupportedClassVersionError in Java is to use same version or JDK and JRE for compiling and running your program.
Example of UnSupportedClassVersionError in Java
You can easily reproduce UnSupportedClassVersionError by using javac of higher JDK and "java" from lower Java version. Let’s see some of examples of UnSupportedClassVersionError in Java:
1) java.lang.UnsupportedClassVersionError: EquityTradingManager (Unsupported major.minor version 49.0)
at java.lang.ClassLoader.defineClass0(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:539)
==>Since we know that major version 49 is supported by JDK 1.5, so these will "java.lang.UnsupportedClassVersionError” will come if JVM used to run this program is lower than Java 1.5.
2) Java.lang.UnsupportedClassVersionError: Bad version number in .class file
3) java.lang.unsupportedclassversionerror unsupported classversion 50.0
==> Compile in JDK 1.6 and running on lower version than Java 6.
4) java.lang.unsupportedclassversionerror unsupported classversion 49.0
==> compiled in Java 5 and running on lower JVM than JDK 5.
5) java.lang.unsupportedclassversionerror bad version number in eclipse.
==> Most of us use eclipse for building and running project some of us also use ant for building project. In eclipse there is some setting related to java source version which if you got incorrect can result in "java.lang.unsupportedclassversionerror bad version number". so make sure you have correct configuration. For example if you compile with source compatible 1.6 you need JRE 6 to execute the program. To check the compiler setting in eclipse go to project ==>Properties==>Java Compiler as shown in image
Important point about UnSupportedClassVersionError in Java:
1) If you encounter UnSupportedClassVersionError, check the JRE version you are using to run program and switch to higher version for quick solution.
2) java.lang.UnsupportedClassVersionError is derived from java.lang.LinkageError, so it will not be detected in compile time and it will only come on runtime, precisely when JVM tries to load a class.
3) Class file format which is identified using major version and minor version. Class file format is assigned when you compile source file and its depends on JDK version used to compile.
4) Its always best practice to use same version of java for compilation and execution to avoid any chance of UnSupportedClassVersionError.
5) UnSupportedClassVersionError is not related to java classpath , so don't confuse this with NoClassDefFoundError or ClassNotFoundException.
Major Class Versions of Various JDK
Following are the major version of class file format in standard JDK environment.
JDK 1.1 = 45
JDK 1.2 = 46
JDK 1.3 = 47
JDK 1.4 = 48
JDK 1.5 = 49
JDK 1.6 = 50
You can also get version of "javac" (used for compilation) and version of "java" (used for execution) as below
C:\equity trading\stocks>javac -version
javac 1.6.0-beta2
C:\equity trading\stocks>java -version
java version "1.6.0-beta2"
Java(TM) SE Runtime Environment (build 1.6.0-beta2-b86)
Java HotSpot(TM) Client VM (build 1.6.0-beta2-b86, mixed mode, sharing)
Now you can identify your JDK version based on class file format version whenever you see java.lang.UnsupportedClassVersionError :)
So next time when you see UnsupportedClassVersionError don't be afraid and follow the best approach based upon your need.
If you like this post you may find my other tutorial how java hashmap works, why String is immutable in java, why wait and notify needs to call from synchronized context interesting.
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