Posts in the “java” category

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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.

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Summary: This page is a printf formatting cheat sheet. I originally created this cheat sheet for my own purposes, and then thought I would share it here.

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, Perl, PHP, Ruby, Scala, and others. This means that your printf knowledge is reusable, which is a good thing.

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

The short answer

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

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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?

Sure. In this tutorial, I’ll show how to declare, populate, and iterate through Java string arrays, including the newer for-loop syntax. 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 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.

Way back in the late 1990s, I wrote a Java CRUD generator, which was based on the work of someone else. It was a static code generator, but like future dynamic frameworks like Ruby on Rails, CakePHP, and others, it scanned the database and generated source code from the database table definitions.

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

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.

Square a number by multiplying it by itself

Here’s how to square a number by multiplying it by itself:

i = 2
int square = i * i

In that case, if you print the value of square, it will be 4.

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Summary: This is a Java SimpleDateFormat (date formatting) example, showing how to convert a String to a Date.

In an earlier example I showed how to use the Java SimpleDateFormat class to convert from a Date to a String, but you can also use the SimpleDateFormat class to convert in the opposite direction, from a given Java String to a Date object.

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

For a long time I appended Java strings together using the + operator to combine them into the output format I wanted, but I always knew that approach was pretty ugly. Fortunately at some point I learned how to use the Java String format method to format my text, and as you’ll see, the resulting code is much cleaner this way.

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 FAQ: How do I populate (initialize) a static HashMap in Java?

In Java 9 and newer you can create and populate a Map like this:

As I started to mention in another blog post, your Java code will be more flexible when you learn to return more-general object references. In most cases other developers only need to see your interface, not your implementation. Put another way, does it matter to anyone else if you used a LinkedList or an ArrayList? If it doesn't matter, then return a List, or perhaps even a Collection.

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

I just needed to add a manifest file to a Java JAR file, and this command worked for me:

Summary: A simple Java JScrollPane source code example.

When you're first learning how to use Java Swing components, like a JScrollPane it can be a little hard to figure out how to get started. To that end I am trying to share several complete Java source code examples that demonstrate how to work with components like these.

Java JFrame FAQ: How do I properly create and display a JFrame? While you're at it, how do I center a JFrame?

In this Java tutorial I'll demonstrate how to create and display a JFrame Other than the comments in the source code, I'm going to keep the code as simple as possible, so I can demonstrate how this works.

I've been getting back into the Java/Swing world during the last few days, and I thought I'd share some example code here. In my current application, one of the things I just worked on was setting the initial JFrame size to a value I liked.

Here's a quick line of Java code that takes a given input string, strips all the characters from that string other than lowercase and uppercase letters, and returns whatever is left:

Problem: In a Java program, you want to determine whether a String contains a certain pattern. The pattern can be a simple String, or a more complicated regular expression (regex).

Today I needed a Java method to remove all the blank characters from a String. I started to write some code with a StringBuffer or a StringBuilder, then thought there must be some other way to do this. It’s not that the StringBuilder/StringBuffer approach is hard, but just that someone must have already solved this problem.