Insert a string in the middle of text file without replacing

Suppose i have a text file named Sample.text. i need advice on how to achieve this:

Sample.txt before running a program: ABCD

while running the program, user will input string to be added starting at the middle for example: user input is XXX

Sample.txt after running a program: ABXXXCD

Basically you've got to rewrite the file, at least from the middle. This isn't a matter of Java - it's a matter of what file systems support.

Typically the way to do this is to open both the input file and an output file, then:

Copy the first part from the input file to the output file
Write the middle section to the output file
Copy the remainder of the input file to the output file
Optionally perform file renaming if you want the new file to have the same eventual name as the original file

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