I was surprised that on installation of JDK, java works, but javac and jar do not. It is necessary to manually add bin-subdirectory to path.
Why it is not done by installation?
Updating the PATH Variable
You can run the Java 2 Runtime Environment without setting the PATH variable, or you can optionally set it as a convenience.
Should I set the PATH variable?
Set the PATH variable if you want to be able to conveniently run the Java 2 Runtime Environment executables from any directory without having to type the full path of the command. If you don't set the PATH variable, you need to specify the full path to the executable every time you run it, such as:
C:> \j2re1.4.1\bin\java MyClass.java
It's useful to set the PATH permanently so it will persist after rebooting.
How do I set the PATH permanently?
To set the PATH permanently, add the full path of the j2re1.4.1\bin directory to the PATH variable. Typically this full path looks something like C:\j2re1.4.1\bin.
To set the PATH permanently, from the start menu, open the Control Panel, and from there, double click the System icon to open the System Control panel. If the System icon is not visible, first click on the "Switch to Classic View" button.