Introduction to Java App Development
Java is one of the most interesting programming languages I have come across since I started to learn to program. It is fast, versatile, and almost used for many things. People think that Java for app development is complex, especially Advanced Java, in App Development. But let me tell you, it is not. First of all, there are very few programming languages that are tough to learn, the ones like Malbolge.
But Java and Advanced Java? Nope. It’s not. It’s like they said in the movie ‘Dark Knight Rises, ‘It needs a less busy mind to do it. Similar is the case for Java App development. One needs to be fully involved in it to ensure things work out properly when developing a Java-based App. It is not as easy as Python or Scheme. But the speed and utilization of resources are far better than the likes of it. Java App development is not for beginners or people who have learned other programming languages. It is only for those with a rock-solid basic Java foundation for app development.
The PreRequisites of Java App Development
So, before you proceed to use Java App development, make sure you know a few things like below:
- Generic Programming
- Java App Development with Network Programming
- Various Java Applets and Web Servlets
- Regexes or Regular Expressions
- Exception Handling
If you don’t know the above terms and how to work with them, then there is no chance you could develop a stable and sensible app. One requires an intense amount of knowledge of the above terminologies to work with them, at least if you have some basics in any programming language and its Java app development.
Generic Programming
You may have heard of high-level or low-level programming and similar stuff. But what exactly is Generic Programming? That is not a term you hear when you work with almost any other programming language. Generic programming mostly became famous with C++ and then Java. Generic programs have lots of techniques. This programming is all about centralizing the Java app development software components to use and reuse them in various manners. Usually, when you try to generalize a program, people do it at the cost of efficiency, and the app development in Java becomes less optimized and slow. And that’s not good. However, the templates used in functions and classes like in C++ are very effective for generic programming since, here, the generalization is possible without the loss of efficiency.
Generic methods and classes in Java enable the app developers to specifically choose a single method declaration and a query of related methods, class declarations, and types. They also support the safety of the compilation time to catch weird behavior types during the compilation.
An example states how to print arrays of multiple types using a mono Generic method.
Code:
public class TestMethod{// The method is pArray which needs to be printed
public static <X>
void pArray( X[] insertArray ){// Displaying all the elements in the array for ( X element : insertArray ){ System.out.printf( "%s ", element );}
System.out.println();
}
public static void main( String args[] )
{
// To Create Integer, Double and Character arrays
Integer[] iArray = { 1, 2, 3, 4, 5 };
Double[] dArray = { 1.1, 2.2, 3.3, 4.4 };
Character[] chArray = { 'C', 'X', 'M', 'A', 'S' };
System.out.println( "Array iArray contains:" );
pArray( iArray ); // Display an Integer array
System.out.println( "\nArray dArray contains:" );
pArray( dArray ); // Display a Double array
System.out.println( "\nArray chArray contains:" );
pArray( chArray ); // Display a Character array
}
}Java App Development with Network Programming
If you are an experienced programmer, even if not in Java but in some other language, the first thing that comes to mind when you hear the term Network Programming is Sockets. Sockets play a vital role in Java app development.
A socket is just one side of the two-way link between two programs running on the same network. The classes used in Sockets represent the connectivity between the client and server sides. And our Java for app development package provides two classes: the socket and the server sockets, which execute the connectivity from the client and server sides together. Though URL connections provide a decent upper-level mechanism for redistributing resources on the Internet, sometimes you need applications that require lower-the-belt network communication, which in our case is using sockets or when you need to develop a client and server App.
For example, when developing a client and server app, the server processes database queries and sends out the current stock price. The client then uses the server’s service to display the required database results to the requesting user and thereby gives stock recommendations to the specific kind of investor. And when this communication is taking place, it should be without any data drop in the same manner as it was sent to the client side so that no incorrect data is transferred.
Thus, the TCP connectivity here helps to provide a dedicated end-to-end communication channel used on the Web by the client and the server application to establish secure communication. And this is where the socket connectivity comes in between. Programs bind these sockets to communicate at their end channels. Then, the client and the server read and write to the required socket as and when needed.
Various Java Applets and Web Servlets
Most of you, if you have used Linux, then you may already know what an applet is. But still, some of you may be confused about what Servlets are and how they play an essential role in Java App development of Java.
So, let us take a look at the significant difference between them and what exactly they are:
1. Java Applets
A Java applet is a predefined piece of code that is written in Java and provided to users. When the user executes the given applet on a Website, it completes within a JVM in a separate process from the browser itself. Thus, whenever you try to run a Java-based applet, you will see a new approach executed if you check your task manager. This is good but at the price of malicious applets configured to give background Telnet access which can be performed without the user knowing that someone else is taking control of his whole computer.
Applets enhance Web-based Apps with an interactive session that basic HTML alone cannot provide. They can even take control of the whole keyboard and mouse and execute specific interactions by themselves. In addition to this, these applets can help in providing a graphic visual UI. This makes the applet suitable for providing some Java for online app development training, playing videos, and similar stuff.
Thus, applets send data over the Web, and users execute them on Java-supported browsers. Most browsers today, like Chrome, Safari, Mozilla, and Opera, support these applets by default without needing extra configuration. These applets can use UI classes and life cycle methods like AWT, initialization, stopping itself, etc.
2. Java Servlets
Servlets play a partially different role in Java app development, but they are essential here. A servlet is partially similar to Applets since it has derived its name from there. However, to be more specific, it is a Java-based language class used to increase the capacity of any server. Web servers use servlets to enhance the ability of applications to handle requests. Servlet is just a part of Java for app development which helps to get going with other languages such as PHP or DotNet. Simply put, it is just an object that acquires and responds to a request.
The servlet container executes servlets with the help of the primary HTTP server. It is a server-side component that does not support a user interface. Servlet Methods are Get and Post.
Regexes or Regular Expressions
Users typically use regular expressions, also known as Regexes, to describe a set of strings that share common characteristics. They can then use these Regexes to scan, modify, or manipulate data. To learn regexes, you must first learn to create specific syntaxes to create other Regexes, and by different regexes, I mean those that go beyond Java’s normal daily usage syntax. Different Regexes differ in their basics and complexity, but once you grasp the fundamentals and their construction, you can comprehend and modify any other regex.
The regex package in Java is called Java.util.regex.
The Java.util.regex package includes three different classes bound together to each other:
- Pattern: A Pattern object consists of a view of compiled regular expression. It doesn’t have any public constructors. However, invoking a public static compile technique will give a Pattern object. Here, the first argument is treated as a regular expression.
- Matcher: This object detects how the above pattern behaves and executes a matching search operation against the given string. Similar to the Pattern class, there are no public constructors here.
- Pattern Syntax Exception: The system does not check this Exception object by default, and it displays syntax errors within regex patterns.
Exception Handling
An exception disrupts the normal flow of the coded instructions when a program executes. If an error occurs inside a method, it creates an exception object and transfers it to the runtime system. The exception object provides detailed information about the type of error, its occurrence time, and whether the program stopped or continued. Throwing an exception refers to the process of creating and transferring the exception object to the runtime system.
After the Exception is thrown, the system tries to find a way to handle it, and a few things are run in an ordered manner to get its details, known as Call Stack.
Following is the data structure as to how this is handled.
The Call Stack
The searching call stack for Exception.
There are, in total, three types of exceptions in Java App development.
1. Checked Exception
The first kind of exception is called the checked Exception. Programmers predict these exceptions and have solutions to handle them already included in the program’s instructions. A checked exception may occur when an online form requires the user to fill in their name. If you accidentally enter a numeric digit, the program should raise an exception and give a prompt stating “invalid entry” instead of just quitting the whole application. Developers consider these exceptions as checked because they expect them to come from the end-user and they have already tested and handled them.
2. The Error
These kinds of errors are those which occur due to an external environment. This is not the application’s fault, but some external event causes the program to quit unexpectedly. An excellent example of this would be something like your program is running already, and due to some power failure, the system shuts down. Then it should raise an exception showing the user that something else apart from the app development in Java has caused the application to end.
3. Runtime Exception in Java App Development
These are exceptions that are not covered in the above exceptions. For example, something like bugs. These exceptions are not anticipated and are raised due to the programmer’s fault. It makes more sense to eliminate the bug than to raise this Exception. At least something is better than nothing.
I could go on and on about Java App development, but these things matter to the core. If you know what these are, you at least have the basics and are ready for the actual Java app development.
Recommended Articles
This is a guide to Java App Development. Here we discuss the introduction, generic programming, various Java applets and web servlets, and exception handling. These are the following external links related to the Java App development –
