Posts in the “java” category

JFrame title FAQ: How do I set the title of a Java JFrame?

Solution

There are two ways to set the JFrame title. First, you can set the JFrame title when you construct your JFrame, like this:

Java exceptions FAQ: How do I create a custom exception in Java?

Solution

The solution is to:

• Create a custom exception class in Java
• Throw the custom Java exception
• In other code, catch the custom exception, and
• Look at the output from our custom exception when we print a stack trace

Java FAQ: How do I initialize/populate a static List (ArrayList, LinkedList) in Java?

Java 9

When you’re using Java 9 and newer — Java 11, 14, 17, etc. — you can use this concise syntax to populate a static List:

Summary: This article provides definitions and descriptions of the Java stack and heap.

I just read a couple of emails about the concepts of a Java stack and heap, and thinking that their descriptions weren’t exactly right, I decided to do a little research. There’s no better source than the source, so directly from Oracle’s Java website, here are definitions for the Java stack and Java heap.

Java String array FAQ: Can you share an example of how to determine the largest String in a Java String array?

Sure, in this tutorial I'll share the source code for a complete Java class with a method that demonstrates how to find the longest String in a Java string array.

Finding the longest string in a Java string array

Here's the source code that shows how to find the longest string in a Java String array:

Java array FAQ: Can you share some examples of how to create arrays in Java (Java object arrays)?

While I generally work with lists and maps in Java, I occasionally need to create object arrays in Java. Since I don't use arrays that often, I thought I'd share some examples here so I can have a handy Java array syntax reference.

A simple Java String array

I work with the String class a lot, and here's how to create a String array in Java:

Java String array FAQ: Can you share some Java array examples, specifically some String array examples, as well as the new for loop syntax that was introduced back in Java 5?

Solution

Sure. In this tutorial, I’ll show how to declare, populate, and iterate through Java string arrays, including the for loop syntax that was introduced with Java 5. Because creating a String array is just like creating and using any other Java object array, these examples also work as more generic object array examples.

Java array FAQ: Can you share an example of how to sort a Java String array?

Sure. The following source code shows how to sort an array of strings. In short, you can easily sort a string array with the Arrays class sort method, shown in bold below:

Java Robot class FAQ: Can you show me an example of how to use the Java Robot class?

Answer: Um, yeah, sure ... I say that a little jokingly. Okay, what really happened is that while developing this Java Robot example code on my Mac, I had to reboot it about 10 times. When you use the Java Robot class, you're poking your head out into the native operating system, and if you mess up with your GUI events -- at least on a Mac OS X system -- a lot of bad things can happen.

Java String FAQ: How do I merge/combine two Java String fields?

Solution

NOTE: If performance is an important consideration, use the StringBuffer approach I show below.

You can merge/concatenate/combine two Java String fields using the + operator, as shown in this example code:

Java/Scala memory FAQ: How do I control the amount of memory my Java program uses (i.e., Java RAM usage)?

Java memory control: Short answer

The short answer is that you use these java command-line parameters to help control the RAM use of your application:

Summary: This tutorial demonstrates how to use the Java SimpleDateFormat class to convert a Java Date to a formatted String.

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:

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 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 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.

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.

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 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 String formatting FAQ: How can I format Java String output?

Java String formatting solution

One way to format Java string output is with the format method of the String class, which works like a “Java sprintf” method. Here are some examples: