Question

I am following this tutorial: http://ant.apache.org/manual/tutorial-HelloWorldWithAnt.html

But I have run into some problems.

Here is what I have done (the code is in ~/src/ant-demo/oata/):

javac -d ~/src/ant-demo/build/classes ~/src/ant-demo/oata/Hello*

java -cp ~/src/ant-demo/build/classes oata.HelloWorld

Here is the error that I get:

Exception in thread "main" java.lang.UnsupportedClassVersionError: oata/HelloWorld : Unsupported major.minor version 51.0
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
Could not find the main class: oata.HelloWorld. Program will exit.

I am using Ubuntu with openjdk-7-jdk.

UPDATE

#java -version

java version "1.6.0_24"
OpenJDK Runtime Environment (IcedTea6 1.11.5) (6b24-1.11.5-0ubuntu1~12.04.1)
OpenJDK 64-Bit Server VM (build 20.0-b12, mixed mode)

#which java
/usr/bin/java

Answer 1

It seems you’re compiling with JDK7, but running with a previous version. Use java -version and which java to know which version of java you’re actually using.