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Generating Random Numbers in Java

In programming, often we need to generate random numbers. All major languages provide functionality to generate pseudo-random numbers. In Java, this functionality is provided by java.util.Random. See example below:

ArrayList and Iterator Example

This example shows how to use an iterator with ArrayList. Iterator can be used with other collections.

import java.util.*;

public class ArrayListIterator {
    public static void main(String[] args) {
        ArrayList al = new ArrayList();
        al.add(new Integer(11));
        al.add(new Integer(13));
        al.add(new Integer(17));

        Iterator itr = al.iterator();
        while (itr.hasNext()) {
            System.out.println(itr.next());
        }
    }
}

output

Splitting strings in Java

Java's split function packs a powerful punch. You can use it to split string on characters, symbols, substrings, a collection of symbols, or even regular expressions.

Skills used in Data Science

Not all data scientist are alike. Some do general work while others focus on domains such as health, technology, or business. They can work in predictive analysis, big data, spatial data, or any combination of these. Based on their requirements they require different technical skills.

Technologies

Following some technology trends that I have observed.

Replacing and removing subtrings in Java

Java's replaceString function is very handy for string and substring modifications.

Data Science

A chemist studies chemical properties of objects. A biologist studies living beings. A data scientist studies data. Data is real. It has real properties. Study of data leads to information and knowledge. Answering questions with data leads to revelation, understanding, and wisdom.

Creating custom exceptions in Java

Java allows programmers to create their own Exceptions. To create and exception, you should inherit from the exception closest to what you wish to create. Following is a generic example to show how to create and use a custom exception.

ArrayList NullPointerException

Java's ArrayList is a great Collection that frees us from IndexOutOfBound, one type limitation, and NullPointerException issues while providing several value-added methods. Naturally, you would be shocked if you encounter a NullPointerException on an ArrayList. The only time, you would encounter this problem is when you fail to initialize the ArrayList.

Reading files in a directory using bash

The following code reads files in a directory called SQL. Then if runs an SQL command with the file name as input. Finally, it deletes the file from the directory.

#!/bin/bash

for file in sql/*
do
  echo "Processing $file\n"
  mysql -u root -pdonut node2 < $file
  rm -f $file
done

Copying a large database from one server to another

Recently, I had to copy a large database from one server to another. I had 100G free on the source server. Unfortunately, the server would run out of memory before the mysqldump would complete. So I had to find a way to make the mysqldumps smaller. This can be done by creating separate dumps for each table. Then I had to compress the files to conserve memory. Following is the script I wrote to accomplish this.

Technologies

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