[+/-] : How to remove duplicate items from an ArrayList

This code example shows how to remove duplicate items from an ArrayList.

  ArrayList arrayList1 = new ArrayList();
    
  arrayList1.add("A");
  arrayList1.add("A");
  arrayList1.add("B");
  arrayList1.add("B");
  arrayList1.add("B");
  arrayList1.add("C");
    
  //Create a HashSet which allows no duplicates
  HashSet hashSet = new HashSet(arrayList1);

  //Assign the HashSet to a new ArrayList
  ArrayList arrayList2 = new ArrayList(hashSet) ;
    
  //Ensure correct order, since HashSet doesn't
  Collections.sort(arrayList2);
    
  for (Object item : arrayList2)
    System.out.println(item);

Note that you will have to sort the ArrayList if you want to be sure that the items remain in correct order by calling the sort method of the Collection class. This will produce the following output:

A
B
C

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[+/-] : How to send a POST Request with Parameters From a Java Class

his example shows how to sent a POST request to a server with attached parameters. Two parameters are sent in the example code below, width and height. We use the URL and URLConnection classes to open the connection to the destination. Then the output stream is retrieved by calling getOutputStream() on the URLConnection object. With the output stream we can write the parameters and then start reading the response from the server using the input stream which we get by calling getInputStream() on the same URLConnection object. We assume there will only be character based content returned from the server so we use the BufferedWriter to read the response line by line.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
/**
 * Main.java
 *
 * @author www.javadb.com
 */
public class Main {
    
    /**
     * Extends the size of an array.
     */
    public void sendPostRequest() {
        
        //Build parameter string
        String data = "width=50&height=100";
        try {
            
            // Send the request
            URL url = new URL("http://www.somesite.com");
            URLConnection conn = url.openConnection();
            conn.setDoOutput(true);
            OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());
            
            //write parameters
            writer.write(data);
            writer.flush();
            
            // Get the response
            StringBuffer answer = new StringBuffer();
            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line;
            while ((line = reader.readLine()) != null) {
                answer.append(line);
            }
            writer.close();
            reader.close();
            
            //Output the response
            System.out.println(answer.toString());
            
        } catch (MalformedURLException ex) {
            ex.printStackTrace();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
    /**
     * Starts the program
     *
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        new Main().sendPostRequest();
    }
}

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[+/-] : how to remove a line from a text file

This example shows how to delete a line from a file. The method removeLineFromFile takes two parameters, the first parameter is the file to remove from and the second parameter is the content of the line to remove. A tempfile is created and written to, except for the content that matches the second parameter. This way very large files can be handled without demanding so much internal memory. The original file is then deleted and the tempfile is renamed to the original filename. For example, the file test.txt is located in the current directory and contains three lines, and we will remove the second line "bbbbb".

aaaaa
bbbbb
ccccc

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.File;
import java.io.FileWriter;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintWriter;

public class FileUtil {


 public void removeLineFromFile(String file, String lineToRemove) {

   try {

     File inFile = new File(file);
    
     if (!inFile.isFile()) {
       System.out.println("Parameter is not an existing file");
       return;
     }
     
     //Construct the new file that will later be renamed to the original filename.
     File tempFile = new File(inFile.getAbsolutePath() + ".tmp");
    
     BufferedReader br = new BufferedReader(new FileReader(file));
     PrintWriter pw = new PrintWriter(new FileWriter(tempFile));
    
     String line = null;

     //Read from the original file and write to the new
     //unless content matches data to be removed.
     while ((line = br.readLine()) != null) {
      
       if (!line.trim().equals(lineToRemove)) {

         pw.println(line);
         pw.flush();
       }
     }
     pw.close();
     br.close();
    
     //Delete the original file
     if (!inFile.delete()) {
       System.out.println("Could not delete file");
       return;
     }
    
     //Rename the new file to the filename the original file had.
     if (!tempFile.renameTo(inFile))
       System.out.println("Could not rename file");
    
   }
   catch (FileNotFoundException ex) {
     ex.printStackTrace();
   }
   catch (IOException ex) {
     ex.printStackTrace();
   }
 }

 public static void main(String[] args) {
   FileUtil util = new FileUtil();
   util.removeLineFromFile("test.txt", "bbbbb");
 }
}

The file test.txt now looks like this:

aaaaa
ccccc

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