There are two java files:
Assemble.java
AssemblyLine.java
Compile these two files by typing
javac Assemble.java
Say you have a source file names "myfile"; to assemle it, type:
java Assemble myfile > myfile.out
This produces two files: The listing file is called "myfile.lst" and the object file is given the name specified after the greater-than sign (myfile.out).
The assembler always produces a warning that if there are any errors, the output is not valid. This is just a reminder -- this message itself is not an error.