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Tip of the Day
Language: Java Language
Expertise: Beginner
Dec 4, 1998

Creating a Guaranteed Unique Filename

Question:
How can a unique filename be constructed that guarantees that it will be unique across processes?

Answer:
There is unfortunately no Java 1.1 analog to the POSIX tmpnam() C function, which generates a unique filename, or tmpfile(), which creates a new file with a unique filename. But Java 1.2 has added this functionality by adding the createTempFile static method to the java.io.File class. This method will create a new file with a unique name based upon a base pattern. During any given run of an application, createTempFile will never create the same filename twice. If for some reason it cannot create a file that did not previously exist, createTempFile will throw an IOException. I cannot conceive of a bulletproof way of implementing this functionality in Java 1.1 using 100% Java code. In fact, Java 1.2's createTempFile relies on native code to implement the method.

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