Read integers from a file, sort, and print.

0

By BestJewSinceJC on Mar 4th, 2010 6:47 am

Since I keep seeing people asking how to read the Integers from a File, I figured this simple snippet might be useful. What it does is it creates a new Scanner Object based on the File Object "test.txt" then it reads all of the Integers from that file, skipping over anything else that was found in the file, and adding the Integers to an ArrayList. It then sorts the ArrayList and prints out the sorted numbers. The file must exist otherwise this example will crash.

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;


public class IntegersFromFile {

	public static void main(String[] args) {
		Scanner file = null;
		ArrayList<Integer> list = new ArrayList<Integer>();
		
		try {
			file = new Scanner(new File("test.txt"));
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		}
		
		while(file.hasNext()){
			if (file.hasNextInt()) list.add(file.nextInt());
			else file.next();
		}
		
		Collections.sort(list);
		
		for (Integer i: list) System.out.println(i);
		
	}

}

2 Years Ago

0

Out of curiosity, what sorting algorithm does the Collections class' sort method use?

kvass

Junior Poster

168 posts since Aug 2009

Reputation Points: 85

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2 Years Ago

0

http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collections.html#sort%28java.util.List%29

It uses a modified merge sort .. of some sort. Hehe.

BestJewSinceJC

Posting Maven

2,772 posts since Sep 2008

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2 Months Ago

0

ok well i tried this but i want to modify it to sort text rather than numbers not sure how to do it I tried this

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner; 

 public class NameSort { 	

public static void main(String[] args) {	
	Scanner file = null;		
[ArrayList<String> list = new ArrayList<String>();]

 		try {	
		file = new Scanner(new File("names.txt"));
		} catch (FileNotFoundException e) {	
		e.printStackTrace();		} 	

	while(file.hasNext()){			
if (file.hasNextString()) list.add(file.nextString());
			else file.next();		}

 		Collections.sort(list); 		


for (String s: list) System.out.println(s); 	
	} 

}

but it doesnt want to work keeps coming back with errors any help would be much appreciated

jade_91

Junior Poster in Training

50 posts since Jan 2012

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1 Month Ago

0

why do you have brackets around the arraylist decleration?

devninja

Light Poster

36 posts since Mar 2012

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