# Using IntelliJ select the desired type (e.g., java.lang.Number) and open subtypes hierarchy.
# Using the toolbar in the Hierarchy window click the button to export the hierarchy into a file.
# The exported file (let's call it init.txt) should look like below:
Number (java.lang)
    Float (java.lang)
    MutableInt (org.apache.commons.lang3.mutable)
    MutableInt (org.apache.commons.lang3.mutable)
    BigFraction (org.apache.commons.math3.fraction)
    BigFraction (org.apache.commons.math3.fraction)
    BigFraction (org.apache.commons.math3.fraction)
    Integer (java.lang)
    MyInteger in MyClass (org.some.package)
# The first step is to treat inner classes which appear as type MyInteger in MyClass to look like MyClass$MyInteger
sed 's/\([[:alnum:]]\+\)$\([[:alnum:]]\+\)/\2$\1/' init.txt > step1.txt
# The second step is to remove whitespaces to have all classes at the same level
sed 's/\s\+//g' step1.txt > step2.txt
# The third step is to bring package name in front of class name and remove parentheses
sed 's/\(.\+\)(\(.\+\))/\2.\1/' step2.txt > step3.txt
# The previous can be done using piped sed expressions as follows
sed 's/\([[:alnum:]]\+\)$\([[:alnum:]]\+\)/\2$\1/' init.txt | sed 's/\s\+//g' | sed 's/\(.\+\)(\(.\+\))/\2.\1/'