Here's a line-processing algorithm that uses rescanning.

    void processLine(String line)
    {
        do
        {
            someReplacement = false
            for each macroName
            {
                replace all occurrences of macroName in line with macroExpansion
                if any replacements made
                    someReplacement = true
            }
        } while (someReplacement)

        print line
    }
                
You might not have seen it before but Java does have a do-while like shown above.  It's commonly used when you want to make at least one pass through a loop but maybe not more.

The line "for each macroName" above corresponds to the line "for (String macroName: macros.keySet())" in the lpphashmap.java example, but instead of printing the macro names and their expansions like the example does, you'll do replacements on the line instead.