In my program, I have a class Sorting, that inputs a file called CountryUnsortedFormat that contains a random list of countries and their populations. The class is supposed to use shellsort to sort the countries by population and display them on the screen.
Here is my code:
package assignment3;
import java.io.PrintWriter;
import java.io.File;
import java.util.Arrays;
import java.util.Random;
import java.util.Scanner;
public class Assignment3 {
public static void main(String[] args) throws Exception{
//Array for handling list of countries
String[] line = new String[238];
//read list of countries into array
readInArray(line);
//unsort the array
unSort(line);
}
static void readInArray(String[] line) throws Exception{
Scanner stdIn = new Scanner(new File("C:/Users/Vicki/Desktop/CountrySortedFormat.txt"));
//Read in countries from sorted file into an array
int k=0;
while (stdIn.hasNextLine()){
line[k]=stdIn.nextLine();
k++;
}
}
static void unSort(String[] line) throws Exception{
PrintWriter out = new PrintWriter("C:/Users/Vicki/Desktop/CountryUnsortedFormat.txt");
//Pick a random int from 1 to 238 called where
//Write where into Unsorted Country Format file
//Make where null
//Repeat until all 238 countries are written in random order
int j = line.length-1;
Random r = new Random();
while (j > 0){
int where = r.nextInt(j)+1;
out.println(line[where]);
line = pop(where, line);
j--;
}
out.close();
}
static String[] pop(int index, String[] line){
String[] newLine = new String[line.length-1];
int offset = 0;
for (int i = 0; i<line.length; i++){
if(i == index){
offset = 1;
continue;
}
newLine[i - offset] = line[i];
}
return newLine;
}
}
class Sorting {
public static void main(String[] args) throws Exception{
//Array for handling list of countries
String[] line = new String[238];
readInArray(line);
shellsort(line);
System.out.println(Arrays.toString(line));
}
static void readInArray(String[] line) throws Exception{
Scanner stdIn = new Scanner(new File("C:/Users/Vicki/Desktop/CountryUnsortedFormat.txt"));
//Read in countries from unsorted file into an array
int k=0;
while (stdIn.hasNextLine()){
line[k]=stdIn.nextLine();
k++;
}
}
static void shellsort(String[] line){
int j;
for(int gap = line.length-1/2; gap > 0; gap /= 2){
for(int i = gap; i < line.length-1; i++){
String tmp = line[i];
for (j = i; j >= gap && getPopulation(line, j-gap) > getPopulation(line, i); j -= gap){
line[j] = line[j -gap];
}
line[j] = tmp;
}
}
}
static int getPopulation(String[] line, int index){
String populationString = line[index].substring(50,65).trim().replaceAll(",","");
int population = Integer.parseInt(populationString);
return population;
}
}
My classes work separately but when put together my program doesn't print to the screen. All it shows is "BUILD SUCCESSFUL (total time: 0 seconds)"
What am I doing wrong?
This is pretty obviously a homework assignment, and it'd be wrong to help you further. I would first organize your code into a more readable format. Eg:
then implement the sort
Which is more or less ripped directly from Wikipedia, and what you have....
This looks like a case of needing better debugging. Drop some breakpoints or some
printlns in populatingline. There's a chance Netbeans isn't printing anything, because there is nothing to print out. Or you could simply be messing up your parsing. You have hard-coded values in there for your substrings and chances are that's where it's breaking. Using a regex or scanner could solve this problem, simply by not being an an unholy cluster of functions. I don't know what your input looks like so I couldn't tell you. However, I know your sort works because I copy and pasted with some random values and ran it myself:The lack of error log
sounds like an environmental issue, or mightcomes down to what you unsorted file looks like, which is most likely wrong since I attempted to answer your previous question which you have since deletedTraversing Through Array Using A Random Int and Unsorting a File
So the difficulty with your code as is that you will not end up with a shuffled array. Instead you will have probably duplicates. Let's run through this with an array of 4
lines = ["Argentina","Barbados","Canada","Dominica"]Iteration 1.
j = 4, let's havewhere = 2and thereforeout = "Canada"Iteration 2.
j = 3, there's nothing to stopwhere = 2again as such,out = "Canada, Canada"To properly scramble your array, I would recommend popping the chosen value To prevent duplicates. Given you are using a plain old array and not an ArrayList you should have a function pop (although I would suggest using an ArrayList):
Your new unSort should like:
Of course there are other shuffles, for instance: you could perform a Fisher-Yates on
lineand then print it out after. I don't fully understand what you're directly asking for, but I imagine it's something like this:Where this guarantees no duplicates. However this has a best case run time of O(n) and a worst case of being an infinite loop.