Posts in the “java” category

Java: JOptionPane showMessageDialog examples (part 1)

I’ve been working with the Java JOptionPane showMessageDialog a lot lately, so I thought I’d create a page here with a number of showMessageDialog examples, sort of a JOptionPane reference page.

I’ll walk you through some JOptionPane examples here, starting with a simple example and then increasing the level of difficulty as I go on.

Java ‘int’ array examples (declaring, initializing, populating)

Java array FAQ: How do you create an array of Java int values (i.e., a Java “int array”)?

Answer: There are several ways to define an int array in Java; let’s take a look at a few examples.

1) Declare a Java int array with initial size; populate it later

If you know the desired size of your array, an you'll be adding elements to your array some time later in your code, you can define a Java int array using this syntax:

Java two dimensional (2d) array examples

It's been so long since I create a two-dimensional Java array in I almost couldn't remember how to do it. Fortunately I did, and I thought I'd include my sample code here in case it will help anyone else.

So, in this quick tutorial, I'll show you how to create a two-dimensional array (2D array) of Java String objects, and then I'll show you how to access each element in the array.

How to create a two-dimensional Java array

First, here's how I create the two-dimensional arrays of strings with this code:

A Java instanceof array example

While working with various "Java instanceof" tests recently, my curiosity was piqued, and I thought I'd take a look at how the instanceof operator works when testing against a Java array.

Scala varargs syntax (and examples)

Scala FAQ: How do I use the Scala varargs syntax (or, What is the Scala varargs syntax)?

You can define a Scala function that accepts a varargs parameter like this:

def printAll(strings: String*) {
    strings.map(println)
}

The only magic in using the varargs syntax is adding the * symbol after the String declaration, as highlighted in this line of code in the function declaration:

Java: How to append text to a file with the FileWriter class

Java file writing FAQ: How do I append text to the end of a text file in Java?

The short answer is that you should create a FileWriter instance with the append flag set to true, like this:

BufferedWriter bw = new BufferedWriter(new FileWriter("checkbook.dat", true));

The rest of this article explains this.

A Java MySQL SELECT example

Summary: This is a Java/MySQL SQL SELECT example, demonstrating how to issue a SQL SELECT command from your Java source code, using a MySQL database.

A Java deep clone (deep copy) example

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Back when I was interviewing for computer programming positions in Boulder and Louisville, Colorado, I found that many interviewers ask questions about Java serialization. After being asked about serialization for the third time, I remembered an old Java deep clone hack that takes advantage of serialization.

Java enum examples/tutorial (an enum reference page)

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Java enumerations FAQ: Can you share some Java enum examples, such as how to declare a Java enum, and how to use a Java enum in a for loop, if/then statement, and Java switch statement?

Sure. As described in the Sun/Oracle Java documentation, “you should use enum types any time you need to represent a fixed set of constants.” Let's take a look at some enum examples to see how this works.

Java: How to square a number

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Java math FAQ: How do I square a number in Java?

Solution

You can square a number in Java in at least two different ways:

  1. Multiply the number by itself
  2. Call the Math.pow function

A `printf` format reference page (cheat sheet) (C, Java, Scala, etc.)

Summary: This page is a printf formatting cheat sheet or reference page. I originally created this printf cheat sheet for my own programming purposes, and then thought it might be helpful to share it here.

Many languages, same syntax

A great thing about the printf formatting syntax is that the format specifiers you can use are very similar — if not identical — between different languages, including C, C++, Java, Python, Perl, PHP, Ruby, Scala, and others. This means that your printf knowledge is reusable, which is a good thing.

Java Jar file: How to read a file from a Jar file

Java jar file reading FAQ: Can you show me how a Java application can read a file from own of its own Jar files?

Here's an example of some Java code I'm using to read a file (a text file) from a Java Jar file. This is useful any time you pack files and other resources into Jar files to distribute your Java application.

Java - read Jar file example #1

The source code to read a file from a Java Jar file uses the getClass and getResourceAsStream methods:

A Java email address validation class

I thought I'd share the source code for my Java email address validator class. I'm not sure if there's a big need for it ... I wrote it a long time ago, and I think I created it because Java's javax.mail.internet.InternetAddress class wasn't validating email addresses as deeply as I wanted it to. For instance, I think it would allow the string "fred" to be a valid email address, but on the internet you really want to see something like "fred@foo.bar". So I think that's where this class comes from.