main function of the class A4, defined in the file a4.java, available from the class web site. You should not need to make changes to this file. The corresponding a4.class file should be what is passed to the Java interpreter.
You should define your own classes for both bindings and filler values. The Binding class is to be the formal parameter type of the newBinding method. The Filler class should have a constructor that takes an integer as its argument.
You may rely on the garbage collector to reclaim storage if necessary.
You should use the mechanism of exceptions to deal with lookup failure.