Java.nio package Runtime error java.lang.UnsupportedClassVersionError.

Question

Hi
I am using nio package and create a java program for file locking (FileLocking.java).
Here is the sample
try {
file = new File("C:/acc.txt");
channel = new RandomAccessFile(file, "rw").getChannel();
     lock = channel.lock(0, Long.MAX_VALUE, true);
try {
          lock = channel.tryLock(0, Long.MAX_VALUE, true);
catch (OverlappingFileLockException e) {
return true;
using wsad 5.1 and jdk1.4 i compiled this program.
While executing i got the following runtime error..
java.lang.UnsupportedClassVersionError: FileLocking (Unsupported major.minor version 48.0)
     at java.lang.ClassLoader.defineClass0(Native Method)
     at java.lang.ClassLoader.defineClass(ClassLoader.java:703)
     at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:133)
     at java.net.URLClassLoader.defineClass(URLClassLoader.java:319)
     at java.net.URLClassLoader.access$400(URLClassLoader.java:92)
     at java.net.URLClassLoader$ClassFinder.run(URLClassLoader.java:677)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.net.URLClassLoader.findClass(URLClassLoader.java:238)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:516)
     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:441)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:448)
Exception in thread "main"
Even if i try to recompile it in command prompt and run, i got the same error.
please suggest me how can i overcome this problem.

Answer 1

UnsupportedClassVersionError means that you are trying to execute a class for a newer version of the JVM on an older version of the JVM.
Version 48.0 is for Java 1.4, so you have compiled your class with JDK 1.4.
The computer you are trying to run the class on, has an older version of Java than 1.4 - check it!
Try recompiling your source files with the "-target" switch, for example if you're running on Java 1.3, try compiling with:
javac -target 1.3 ... FileLocking.java