17-reasons-why-exercise-makes-you-happy-infographic

[Infographic] 17 Reasons Why Exercise Makes You Happy

 One of the most frequent promises people make is to get fit by working out more. Exercising regularly is also one of the hardest promises for people to keep – as the experts at TopStretch.com can attest to. Stressful schedules and day-to-day life tends to get in the way of our wellness goals. People kick start their new healthy outlook with good intentions and gym memberships and then abandon them within a month or so.

It turns out that exercising is one of the best commitments you can make for yourself. Most people know that working out helps people lose weight. Did you know that it also provides emotional benefits such as reduced anxiety and a better self-esteem? It can also sharpen your memory and increase energy levels. Exercise is truly good for our bodiesboth inside and out.

If you need motivation to help keep your workout plan on track, check out this infographic to see some of the unexpected benefits of hitting the gym or running trail on a regular basis.

 

’17

deleteme

Things every Java developer must know about Exception handling

Exceptions are one of the most misunderstood (and misused) features of the Java programming language. This article describes the absolute minimum every Java developer must know about exceptions. It assumes that the reader is somewhat familiar with Java.

Historical Perspective

Back in the heyday of the “C” programming language, it was customary to return values such as -1 or NULL from functions to indicate errors. You can easily see why this isn’t a great idea – developers had to check and track possible return values and their meanings: a return value of 2 might indicate “host is down” error in library A, whereas in library B, it could mean “illegal filename”.

Attempts were made to standardize error checking by expecting functions to set a global variable with a defined value.




deleteme

James Gosling and other designers of the language felt that this approach would go against the design goals of Java. They wanted:

  1. a cleaner, robust and portable approach
  2. built in language support for error checking and handling.

Luckily, they didn’t have to look too far. The inspiration for handling errors came from a very fine language of the 60’s: LISP.

Exception Handling

So what is exception handling? It is unconventional but simple concept: if an error is encountered in a program, halt the normal execution and transfer control to a section specified by the programmer. Let’s look at an example:

try {
   f = new File("list.txt"); //Will cause an error if the file is not found...
   f.readLine;
   f.write("another item for the list");
   f.close();
} catch (FileNotFoundException fnfe) { // ... and transfer control to this section on error.
   // Do something with the error: notify user or try reading another location, etc

}





Exceptions are exceptional conditions that violate some kind of a “contract” during program execution. They can be thrown by the language itself (e.g. use a null reference where an object is required) or by the developers of program or API (e.g. passing date in British format instead of American). Some examples of exceptions are:

  • Accessing index outside the bounds of an array
  • Divide by 0
  • Programmer defined contract: Invalid SQL or JSON format

Exceptions disrupt the normal program flow. Instead of executing the next instruction in the sequence, the control is transferred to the Java Virtual Machine (JVM) which tries to find an appropriate exception handler in the program and transfer control to it (hence disrupting the normal program flow).

Checked and Unchecked Exceptions

Before we look at the exception classes in Java, let’s understand the two categories of exceptions in Java:

Checked exceptions – You must check and handle these in your program. For example, if you are using an API that has a method which declares that it could throw a checked exception, you must catch the exception each time you call that method. If you don’t, the compiler will notice and your program will not compile. The designers of the Java wanted to encourage developers to use checked exceptions in situations from which programs may wish to recover: for example, if the host is down, the program may wish to try another address.

Unchecked exceptions on the other hand are not required to be handled or caught in the program. For example, if a method could throw unchecked exceptions, the caller of the method is not required to handle or catch the exceptions.

Remember: Checked exceptions are mild and normally programs wish to recover. They must be caught and this rule is enforced by the compiler. The compiler doesn’t care whether you do or do not catch unchecked exceptions.

Many people find dichotomy between checked and unchecked exceptions confusing and counter-intuitive. Discussing the arguments from both sides are beyond the scope of this post.

Parent of all exception classes: Throwable

All exceptions in Java descend (subclass) from Throwable . It has two direct children:

  1. Exception
  2. Error

Error and its sub-classes are used  for serious errors from which programs are not expected to recover,  i.e. unchecked exception.

Exception and its sub-classes are used for mild errors from which programs may wish to recover, i.e. checked exception. Right? Well, there is a twist. There is just one sub-class which is different, that is, unlike it’s parent the Exception class, it is unchecked. It’s called the RuntimeException.deleteme

Checked exception classes (mostly): Exception

Exception and its sub-classes must be caught and as such they force the programmer to think (and hopefully) deal with the situation. It is a signal that something didn’t go as intended along with some information about what went wrong, and that “someone” should do something about it. (e.g. car’s dashboard indicating that the battery needs service).

According to official documentation:


These are exceptional conditions that a well-written application should anticipate and recover from. For example, suppose an application prompts a user for an input file name,  [..] But sometimes the user supplies the name of a nonexistent file, and the constructor throws java.io.FileNotFoundException. A well-written program will catch this exception and notify the user of the mistake, possibly prompting for a corrected file name.

Source: The Java Tutorials

RuntimeException

RuntimeExceptions are used to indicate programming errors, most commonly violation of some established contract. They make it impossible to continue further execution.

For example, the contract says that the array index mustn’t go past [array_length – 1]. If you do it, bam, you get a RuntimeException. A real world analogy would be pumping diesel into a gasoline car: the unwritten contract says that you must not do it. There are no  signals, just the white smoke before the car comes to a grinding halt after a while. The message: it was your fault and could’ve been prevented by being smarter in the first place.

These are exceptional conditions that are internal to the application, and that the application usually cannot anticipate or recover from. These usually indicate programming bugs, such as logic errors or improper use of an API.

Source: The Java Tutorials

Error

These exceptional circumstances are like “act-of-god” events. Going back to our previous analogy, if a large scale alien invasion were to happen, there is nothing you could do your protect your car, or yourself (unless your last name is Ripley). In Software world, this amounts to the disk dying while you are in the process of reading a file from it. The bottom line is that you should not design your program to handle Errors since something has gone wrong in the grand scheme of things that are beyond your control.

These are exceptional conditions that are external to the application, and that the application usually cannot anticipate or recover from. For example, suppose that an application successfully opens a file for input, but is unable to read the file because of a hardware or system malfunction.

Source: The Java Tutorials

It’s not so black and white

Checked exceptions are often abused in Java. While Java forces developers to catch unchecked exceptions, it cannot force them to handle these exceptions. It’s not hard to find statements like this even in well written programs:

try {
   Object obj = ...
   Set<String> set = ...
   // perform set operations
} catch (Exception e) {
   // do nothing
}

Should you ever catch Runtime Exceptions?

What’s the point of catching RuntimeExceptions if the condition is irrecoverable? After all, if you were catching every possible run-time exception, your program will be cluttered with exception handling code everywhere.

RuntimeExceptions are rare errors that could be prevented by fixing your code in the first place. For example, dividing a number by 0 will generate a run time exception, ArithmeticException. But rather than catching the error, you could modify your program to check the arguments for division function and make sure that the denominator > 0. If it is not, we can halt further execution or even dare to throw a exception of our own: IllegalArgumentException.

In this case, the program got away by verifying the input parameters instead of catching RuntimeExceptions.

So when is it OK for an application to catch RuntimeExceptions?

A while back, I architected a high-performance traffic director with the goal of operating in the proximity of 10,000 transactions per seconds (TPS). The project had a very high availability criteria and one of the requirement was that it “must-never-exit”.

The director performs minimum amount of processing on each transaction before passing it further. Transactions came in two flavours, call them: A and B. We were only interested in transactions of type A. We had a transactions handler to process type A. Naturally, it “choked” run time exceptions when we passed in transactions of type B. The solution? Create a function and pass it every single transaction. If it returned true, we continued to further processing. Otherwise, we simply ignored the transaction, and continued onto the next one.

boolean checkFormat(Transaction t) {
//return true if the t is of type A. false otherwise.
}

This worked well, except…..

… the analysis showed that this function returned false only once a year. The reason, 99.99999999999999% transactions were of type A. Yet, we were subjecting every single transaction to be checked. This does not sound so bad, but due to the nature of transactions, the only way to differentiate was by doing expensive String comparison on various fields.




When this finding was brought to my knowledge, I immediately had the `checkFormat(…)` function removed and instead let the handler do it’s course and throw RuntimeException upon encountering transaction of type, B. When the exception gets thrown once a year, we catch it, log it and move onto the next transaction. The result: improvement in performance, and room to squeeze in additional calculations.

Summary

Exceptions in java are either checked or unchecked. Checked exceptions must be caught in the program otherwise the compiler will complain. While Java encourages developers to follow certain guidelines when it comes to exception handling, there aren’t any hard and fast rules and the rules are often bent.

Source https://10kloc.wordpress.com

keep-this-java-cheat-sheet-on-hand-while-youre-learning-to-code

Keep This Java Cheat Sheet on Hand While You’re Learning to Code

If you’re looking to learn a programming language that’s cross-platform and easily accessible, Java is one of the most practical languages out there. This handy cheat sheet helps you keep track of the basics while you begin to learn.


4dd480fcce8218568fd05aa3909bca56




Java has been around for quite some time and it’s one of the most widely used languages when it comes to web apps, applets, and even some Android app development. This cheat sheet, from Princeton University’s Introduction to Programming in Java course, makes a great reference for the basics you need to know, like structure, input/output, data types, and functions. Check out the the link below to dig a little deeper into Java at Princeton University’s web site.

 

10-common-mistakes-that-java-beginners-often-makes

10 Common Mistakes That Java Beginners Often Makes

Since Java advent in 1995, Java has changed our lives and exceeding the expectations of people. The Sun Microsystem team that worked on the clock to develop this programming language targeted digital television industry. So, Java was too advanced at that time, Java was also perfect for the internet and other applications.

Over the time, Java has spread everywhere and it’s created own special place in programming world. The language is easy to learn but most of people do 10 common mistakes in Java programming.

This list is based upon the study of 250,000 java programming beginners from all over the world by the Data scientists. Using around 37 million compilations, they revealed the most common errors a developer makes during coding in Java.

10 Common Mistakes Every Beginners Java Programmers Makes





Let’s go ahead, here’s is top 10 most common errors made by every beginner Java programmer.

  1. Unbalanced parentheses, curly braces, brackets, and quotation marks, or using these different symbols interchangeably, such as in: while (a == 0].
  2. Invoking methods with wrong arguments or argument types, such asin:get(“abc”).
  3. Control flow can reach end of non-void method without returning, such as in:
1
2
3
4
5
6
7
<em>public int foo(int x)
{
  if (x &lt; 0)
    return 0;
  x += 1;
}
</em>




  1. Confusing the assignment operator (=) with the comparison operator (==), such as in: if (a = b).
  2. Ignoring or discarding the return value of a method with non-void return type, such as in: toString();.
  3. Use of ==instead of .equals to compare strings.
  4. Trying to invoke a non-static method as if it was static, such asin:toString();.
  5. Class claims to implement an interface, but does not implement all the required methods, such as in:class Y implements ActionListener { }.
  6. Invoking the types of parameters when invoking a method, such as in:foo(int x, String s);.
  7. Incorrect semicolon in ifstatements or forand while loops, such as in: if (a==b); return 6;

Source https://techxerl.net/

common-multi-threading-mistakes-in-java

Common Multi-threading Mistakes in Java – Calling run() instead of start()

Writing multi-threaded and concurrent programs is not easy, not even in Java.  Even senior developers, including myself, make mistakes while writing concurrent Java applications. This is also one of the trickiest area of Java programming language, where misconceptions outnumbers concepts. Considering amount of misconception an average Java programmers has about multi-threading and concurrency, I thought to start a new series about common multi-threading mistakes done by Java programmers; what is better way to learn from common real word mistakes. Learning from mistakes has another name Experience, but if you only learn from your mistakes then there is only limited things you can learn, but if you learn from other peoples mistake, you can learn much more in short span of time. Have you ever thought, Why writing multi-threaded code is difficult? IMHO, primarily reason for this is that it multi-threading makes it hard for a code to speak for itself. Programmer read code sequentially to understand how it’s executed, but it is only correct if one and only one thread is executing it. That’s why Single threaded code are easy to read and debug. As soon as two threads comes into picture, It become very difficult to make prediction about how your code behave, especially in the absent of any synchronization rules e.g. rules enforced by Java Memory Model. Without JMM you can not make correct prediction about your code in a multi-threaded environment, because it’s possible for one thread to stop at arbitrary point and another thread at different point. Situation becomes even more tricky if those threads are sharing data between them e.g. in form of objects, a poorly written multi-threaded program can cause deadlock, race condition and responsiveness issues, which will prevent a Java application to fulfil it’s promise. I hope, in this series we can learn from each other’s mistake and take a step forward on writing correct multi-threaded application in Java.

Using Run Instead of Start

I am starting with one of the simplest example, this is very common mistakes by junior programmers and caused by half knowledge. They know that anything written in run() method of Runnable interface or Thread class will execute in another thread, but doesn’t know how to create another thread in JVM.

Consider following code :


class KingKong {

    public static synchronized void main(String[] args) {
        Thread t = new Thread() {
            public void run() {
                kong();
            }
        };

        t.run();
        System.out.print("King");
    }

    public static synchronized void kong() {
        System.out.print("Kong");
    }
}

What Does It Print?
(a) KingKong
(b) KongKing
(c) It varies
(d) Compile time error

We had this question in our Java written test and you will be surprised by the percentage of answers, whopping 50% answers It varies, 10% says compile time error, another 15% picks answer a, KingKong and rest of 25% chooses KongKing. We also ask to write explanation of why they choose a particular answer, just to avoid picking someone who is guessing their way. The 50% developer, who chooses It varies, mentioned that there is no guarantee when a thread will start, so it possible that if main thread finishes first it will print KongKing and if new thread executes before main thread. Wow, what do you say about these developers, seems a decent lot of programmer who knows some part of multi-threading but overlooked critical detail. The next 10% programmer, who chose Compile time error were unsure whether main method can be synchronized or not and thought that compiler will not like. Next 15% says because “King” comes first in code, it will be printed first and “Kong” will be printed later. The Last 25% who chose “KongKing” are the people who got it correct. We were literally disappointed with these numbers because it wasn’t such a difficult of tricky question, but I agree some time it’s difficult to spot a typo and that’s what makes this error very hard to debug.

Why Code Print KongKing and not KingKong?




Common Java Multi-threading Mistakes

Correct answer is “KongKing” and this is because of one typo in code. Intention of this code is to create a multi-threaded program, but because of t.run() it actually turned into a single threaded program. In Java, though it is true that calling Thread.start() will call Runnable.run() method but complete truth is that calling start() actually creates a new thread, and that new thread executes the run() method. If you directly call the run() method then no new thread will be created and the thread which is running the code will go to run() and execute it fist and then comeback to it’s previous point. Like in this case, main thread will execute run() method first, and thus print “Kong” before coming back and printing “King”, that’s why output is “KongKing”. When I quizzed about these to some programmer who were otherwise good but got this answer incorrect insisted that run() will call on new thread because they are calling as t.run() where t is new thread object. So apart from typo, this is the key misconception some Java programmer has. This is even more fundamental in nature because it highlight difference between code and thread. Here definitely run() is called on t, which is a new thread, but the thread which is executing code is not thread t, but main thread. t is not yet started because you have not called the start() method. If you copy past above code in Eclipse IDE and debug it you will see the truth, as shown below.

How to debug Multi-threading Programs in Eclipse

You can see that we have put the breakpoint right at the point where run() method is called i.e. t.run(). When you step Into this method, you will see that main thread is executing run() method and not the new thread. Now if we just changed the t.run() to t.start(), your program will become multi-threaded and a new thread will be created when main thread will execute line t.start(), later run() method will be called in this new thread, here is the screenshot of that.

Difference between Start and Run Method in Java thread

That’s all in first post of my new series of common Java Multi-threading mistakes. Always use start() method to start new threads and make your program multi-threaded, don’t call run() method directly. Compiler doesn’t prevent you but it create subtle bugs. By the way, difference between start() and run() method is also very common question on Java interview. Let me know how do you find this article and don’t forget to share what multi-threading issues you have faced and what lessons you have learned from them. On closing note, I would share one important tip to understand multi-threading better, debug it. Yes debugging will tell you how many threads are currently executing your code, you can see their stack trace, values of variables they are holding and on which lock they are locking. Debugging multi-threaded program is not easy, but once you do it couple of times, you will find it immensely useful.

Source http://javarevisited.blogspot.in/