Top Ten Coding Errors that Java Developers Will Make

Java Development | Coding Errors and Problems

Java developers often make mistakes, but learning from them can help to ensure that they don’t get repeated. Have a look at the list compiled by our staff of experts.

Anyone who programs fairly regularly makes mistakes in Java, and beginners often struggle with the language. It’s a perfectly natural thing, and many people make the same mistakes over and over again. The following are what are considered to be the top ten list of the errors that most people end up making along with how to spot and fix them. We offer java assignment help.

These are only some of the many errors that most programmers end up making. It’s impossible to completely get rid of every possible error from the entire coding process, but with practice and care it’s possible to avoid constantly repeating the same ones. All programmers encounter the same sorts of problems.

It’s comforting to note that everyone ultimately makes the same types of mistakes irrespective of their experience level! While not every error could be featured here, this is a strong list that’s based on the collected experiences of those who posted to popular Newsgroups that carried information about Java programming. You can read java questions and answers.

The Top Ten Java Coding Errors

java questionsNull pointers are probably the most common error that Java programmers make, and it’s hard to find because compilers can never check for them. Whenever an attempt is made to access an object that has a null reference, the Java Virtual Machine will generate a NullPointerException. There are innumerable causes of null pointers. It generally means that an object hasn’t been correctly initialized or that the return value of a function hasn’t been properly checked.

Many functions return null in order to indicate an error condition. Unless you check return values you would never know what’s going on. Normal testing might not even pick it up, because this is part of an error condition. Don’t ever let your users end up finding the problem for you! If the API function indicates that a null may returned, so make sure to check this out before using the object reference.

Another cause is wherever an initialization feature has been sloppy or otherwise conditional. Take a look at the following code snippets:

public static void main(String args[])


String[] list = new String[3];

int index = 0;

while ( (index < args.length) && ( index < 3 ) )


list[index++] = args[index];


for (int i = 0; i < list.length; i++)


if (list[i].equals “-help”)




if (list[i].equals “-cp”)





This code is a ridiculous example, but it does help to illustrate a fairly common mistake. Sometimes a user enters three or more parameters and the code will run fine, but if nothing is entered then a NullPointerException springs up uncomfortably at runtime. Variables from arrays of strings will be initialized, but sometimes they might not be. Check before attempting to access a variable in an array that isn’t equal to null.

java questions and solutions to themCapitalization errors are exceptionally common. It’s very simple to make these types of errors and sometimes it’s easy to look at a malformed variable or method and still not see that something’s wrong. There’s no silver bullet that can help detect this kind of error, but keep in mind that all methods and any member variables in the Java API begin with lowercase letters, but use uppercase letters whenever a new word begins. This explains things like getIntValue() and such.

java assignment-help

image credit:

 java tricksIt’s really easy to access non-static member variables from inside of the static method. This is especially true when calling just about anything from inside of main. Programmers who are first introduced to Java will often have problems because there’s no need to create an instance of the class in order to invoke the main method. The Java Virtual Machine can call the class TheProgram by going:

TheProgram.main ( command_line_args );

This means that there isn’t any instance of TheProgram since it doesn’t have any other member variable to access at all. Take the following example to see how this can generate a nasty compiler error message:

public class StaticSoftware


public class StaticDemo


public String my_fresh_variable = “thedata”;

public static void main (String args[])


System.out.println (“This generates a wicked compiler error” +

my_fresh_variable );



useful java tricksHaving some problem with a comparison assignment is extremely common. It’s an easy error to make, especially for those who worked in other languages like Pascal. In Pascal this is the code for assignment:


and this is the code for comparison:


Unfortunately = and == code lines are used in Java, which can confuse many programmers. It was actually a poor decision on the part of the developers, and mixing them usually gives an error something like “Cannot convert theVariable to boolean” because it tries to compare something that isn’t there.

fixing coding errorsThe thing that is so annoying about mistyping the name of a method when overriding it is that compilers won’t pick up on it, and the problem can be really frustrating when it comes to manual detection. The symptom of this error will be that the code isn’t called. If you think that the method has ever skipped over its code, then it’s a code idea to consider this possibility. Consider investing in a good quality trace debugger like Visual J++ from Microsoft or perhaps the JBuilder package from Borland. They’re both good options for stepping through some code line-by-line.

common coding errorsAnother major problem with comparisons come from a different aspect of the == operator. The == is used to compare two separate individual object references to see if they point to eh same objects. It’s not possible to compare two strings for equality by using the == operator. This requires the .equals method instead, which is inherited by all of the classes from the java.lang.Object class. The correct way to do this is:

if ( (ghi + jkl).equals(“ghijkl”) )

passing by valueThere’s often confusion over passing by value, and some people have trouble with the whole concept of passing by reference. This is a very frustrating problem to diagnose, since when you look at the code you might be sure that it’s one way or the other. Java uses both, which makes things rather difficult. Whenever you pass Java an object you are passing by reference. This includes:




You’re passing by value whenever you use a primitive data type like:





Keep in mind that String contains no methods by which to modify its contents, which means you might as well be passing by value at the end of the day.

writing exceptionWriting in blank exception handlers is a tempting practicing, and it’s great to just ignore errors, but if you run into problems later it’s hard to see what went wrong in the first place. It’s a much better idea to put a try catch Exception code block:

catch (Exception e)


System.out.println (“Err – ” + e);


around anything in order to help you note what kinds of things went wrong in a pinch. It will ease the pain when it comes to debugging, which is an already annoying practice anyway as necessary as it is.

java codingJust about everyone who comes in from a C or C++ background will find that Java is zero-indexed and move right in easily, but others coming in from other languages might not find things so simple. Arrays are always zero-indexed in Java, which means that the first element’s index is actually zero and not one. This makes code look like so:

String strArray = new String[3];

strArray[0] = “This is the first string”;

strArray[1] = “This is the second string”;

strArray[2] = “This is the third string”;

This can be very awkward for people who aren’t really familiar with coding things in this fashion, but a little practice can make things go much more easily.

java api codePreventing concurrent access to shared variables can help to avoid creating some unusual situations. Such programs aren’t just limited to various types of multi-threaded applications or applets. Those who write Java API code or use Java Beans might find that their code may not be thread-safe either. Those who never write a single application that uses threads will often find that some other person who uses their thread might. For the sake of their sanity, it’s important to ensure that nothing weird might happen.

public class TheCounter


private int counting = 0;

public synchronized void setCount(int amount)


counting = amount;


public synchronized int getCount()


return counting;



For more java assignment help don’t hesitate to get in touch with our service!