JDK7.0b21\bin>java -version
java version "1.7.0-ea"
Java(TM) SE Runtime Environment (build 1.7.0-ea-b21)
Java HotSpot(TM) Client VM (build 11.0-b07, mixed mode)

The following result is observed on Windows2000 and XP. Other demos behave in the same way.
JDK7.0b21\demo\applets\Animator>DK\JDK7.0b21\bin\java -jar Animator.jar
Exception in thread "main" java.lang.NoClassDefFoundError:
Caused by: java.lang.ClassNotFoundException:
        at java.net.URLClassLoader$1.run(URLClassLoader.java:221)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:209)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:324)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:269)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:337)
Error: Could not find the main class.
Error: A JNI error has occurred, please check your installation and try again

Swing demos work fine.