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javaprogram-entry-pointclassname

How to run Java class without knowing a class name

I have a content of compiled Java class as a binary file (named X.class). Let's assume it has some class inside with a proper main method, but I don't know original class name (and it's not X).

How can I run it with java using single command line?

Solution

  • You can get the name of the class using javap -c <filename>. From that point on, it's just shell games. This works on OS X:

    java $(javap -c File.class | head -n 2 | tail -n1 | cut -f3 -d\ )

    Note the space after the \ in the subshell - this is requires to isolate the class name.

    Update based on @nikolay-vyahhi feedback: If you're not sure at which position the class name will appear (e.g. when it's unknown whether the class is public or not), you can use tr and grep, like so:

    java $(javap -c File.class | head -n2| tail -n1 | tr [:space:] \\n | grep -A1 "class\|interface" | tail -n1)