Read from file and display nonduplicate words in ascending order.

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Java

I am asked to write a program to read from a text file and display nonduplicate words in ascending order. The text file is passed as a command-line argument. Basically, I've managed to write a program to read a predefined String and display all nonduplicates. All is left to do is to read from a file. This is something I am not able to comprehend. Thanks a lot. Here is my code:

import java.util.*;

public class NonduplicateWords {
	public static void main(String[] args) {

		String text = "Testing. I have a testing text. Have a great day";

		TreeSet<String> set = new TreeSet<String>();
		String[] words = text.split("[ \n\t\r.,;:!?(){}]");
		for (int i = 0; i < words.length; i++) {
			String value = words[i].toLowerCase();
			if (words[i].length() > 0)
				set.add(value);
		}
		for (Object element: set)
			System.out.println(element.toString() + " ");
	}
}