Thread: Basic Java question

I'm just starting to learn some Java from a .NET, C#, and C++ background. Anyways the code presented to me is below, with a few basic questions following:

package com.SCM.FRS;
 
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Writer;
import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Deque;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Vector;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;
 
public class FileComparison {
 
	/**
	 * 
	 * @param f file to read in
	 * @return rows in the file
	 * @throws IOException
	 */
	private static Deque<String[]> getCollumns(String f) throws IOException{
		FileInputStream fstream = new FileInputStream(f);
		DataInputStream input = new DataInputStream(fstream);
		BufferedReader in = new BufferedReader(new InputStreamReader(input));
		//Header
		String line = in.readLine();
		//Header 2 then collumns 
		Deque<String[]> values = new ArrayDeque<String[]>();
 
		while (in.ready()){
			line = in.readLine();
			String[] types = line.split("\\|");
			values.add(types);
		}
		return values;
	}
 
	/**
	 * 
	 * @param args [0] is the new file [1] is original
	 * @throws IOException
	 */
	public static void main (String args[]) throws IOException{
		if (args.length != 2){
			System.out.println(args.length);
			System.out.println("This program must have two inputs");
			System.out.println("First is the new file, second the original");
			System.exit(0);
		}
		Deque<String[]> newFile = getCollumns(args[0]);
		Deque<String[]> oldFile = getCollumns(args[1]);
		//I am assuming header is the same for both of them
		String[] headers = newFile.pop();
		oldFile.pop();
		HashMap <String, Integer> hash = new HashMap <String, Integer>();
		HashMap <String, String> examples = new HashMap <String, String>();
		//HashMap <String, File> files = new HashMap <String, File>();
		String fileBase = args[0].substring(0,args[0].lastIndexOf("."));
		File report = new File(fileBase + "_report_summary.txt");
		report.createNewFile();
 
		HashMap <String, Vector<String>> buffs = 
			new HashMap <String, Vector<String>>();
 
		for (int i = 0; !newFile.isEmpty(); i++){
			String[] newInput = newFile.pop();
			String[] oldInput = oldFile.pop();
			for (int j = 0; j < newInput.length && j < oldInput.length; j++){
				if (!newInput[j].matches(oldInput[j])){
					String message = "On row " + i + " was: " + oldInput[j] 
					                          + " is now " + newInput[j] + "\r\n";
					if (hash.containsKey(headers[j])){
						hash.put(headers[j], hash.remove(headers[j]) + 1);
						/*File f = files.get(headers[j]);
						Writer output = new BufferedWriter(new FileWriter(f, true));
						output.append(message);
						output.close();*/
						Vector <String> vec = buffs.get(headers[j]);
						vec.add(new String(message));
					}else{
						Vector <String> vec = new Vector<String>();
						vec.add(new String(message));
						buffs.put(headers[j], vec);
						hash.put(headers[j], 1);
						examples.put(headers[j], message);
					/*	File f = new File (fileBase + "_" + headers[j] + ".txt");
						f.createNewFile();
						Writer output = new BufferedWriter(new FileWriter(f));
						files.put(headers[j], f);
						output.write(message);
						output.close();*/
					}
				}
			}
		}
		Collection<String> examplesDump = examples.values();
		Collection<String> examplesKeys = examples.keySet();
		Iterator<String> itter = examplesDump.iterator();
		Iterator<String> itterKeys = examplesKeys.iterator();
		while(itter.hasNext()){
			Writer output = new BufferedWriter(new FileWriter(report, true));
			String key = itterKeys.next();
			output.write(key + "has been changed " + hash.get(key) + "times\r\n");
			output.write(itter.next() + "\r\n");
			output.close();
		}
 
		Collection<Vector<String>> buf = buffs.values();
		Collection<String> bufKeys = buffs.keySet();
		Iterator <Vector<String>> itt = buf.iterator();
		itterKeys = bufKeys.iterator();
		ZipOutputStream zip = new ZipOutputStream(new FileOutputStream(fileBase + "_report.zip"));
 
		while(itt.hasNext()){
			/*File f = new File (fileBase + "_" + itterKeys.next() + ".txt");
			f.createNewFile();
			Writer output = new BufferedWriter(new FileWriter(f));*/
			String name = new File(args[0]).getName();
			name = name.substring(0,name.lastIndexOf("."));
			zip.putNextEntry(new ZipEntry(name + "_" + itterKeys.next() + ".txt"));
 
			Vector <String> messages = itt.next();
			for (int i = 0; i < messages.size();i++){
				zip.write(messages.elementAt(i).getBytes());
			}
			zip.closeEntry();
		}
		zip.close();
	}
}

1. In the line that says "private static Deque<String[]> getCollumns(String f) throws IOException{" what is the getCollumns(string f) ... part mean? So far I've only understood that you have private static and then function name
2. The comment says f is the file to read in, however where do you set this variable to point to the file you want the program to read?

Hello fred2028,
getColumns would be the name of the method and (String f) shows that the method takes 1 parameter of type string. The Deque<String[]> part is the method's return type. As for setting f, you can set it by using a String literal when you call the method e.g. getColumns("C:\some_text_file"), or you could create a String variable in the main method like String file = "C:\some_text_file" and then pass that in the method: getColumns(file).