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What is Thread in Java

Java , Thread
What is Thread in Java

What is Thread in Java?


Java Thread is an independent path of execution within a program which can run in parallel with other existing Threads.

Now lets talk about Process.

A process is a self contained execution environment and it can be seen as a program. However a program itself contains multiple processes inside it. Java runtime environment runs as a single process which contains different classes and programs as processes.

So we can say that, thread can be light weight process because it require less resources and also multiple threads can share the same resource. Java provides built-in support for multi-threaded programming.

Let’s summarize  in points:

1. The main purpose of multi-threading is to provide simultaneous execution of two or more parts of a program. Each such part of a program called thread.

2. Threads are lightweight processes, they share the common memory space. 

3. In Multi threaded environment, programs that are benefited from multi-threading, utilize the maximum CPU time so that the idle time can be kept to minimum.

Now lets talk about the state of a thread. Thread can be in one of the following states:-

NEW – A thread that has not yet started is in this state.
RUNNABLE – A thread executing in the Java virtual machine is in this state.
BLOCKED – A thread that is blocked waiting for a monitor lock is in this state.
WAITING – A thread that is waiting indefinitely for another thread to perform a particular action is in this state.
TIMED_WAITING – A thread that is waiting for another thread to perform an action for up to a specified waiting time is in this state.
TERMINATED – A thread that has exited is in this state.
A thread can be in only one state at a given point in time.








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Simple Deadlock Explanation

Java , Thread
Simple Deadlock Explanation
Deadlock Explanation with Example.

Deadlock means, it is a situation where 2 or more threads are blocked and waiting for each other.

Let's take an example, in the office we have shared printer and scanner where employees has ability to do scanning and printing.

1. Deepak has bunch of documents that it wants to print first and also want to take a scan later.
(Print and Scan)
2. Rohit has bunch of documents that it wants to scan first and also want to take a print later.
(Scan and Print)

Thread 1 ------ (Got Printer) ------ (Need to Scan) (Blocked)
Thread 2 -------(Got Scanner) -----(Need to Print) (Blocked)


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Reverse Integer in Java.

Java ,
Reverse Integer in Java.

Algorithm 

Reversing Integer is very easy, start collecting the digits from the back of the number until no digits is remaining.

How we will get the last digit of a number?
when a number is Mod by 10, we will get the last digit of a number. 
Example  int lastDigit = number % 10.

We just collected the last digit, so now we need to get the remaining number to work on except the last digit which we already worked on, how we will get the remaining number except last digit?
By dividing the number by 10. Example: int remainingNumber = number / 10.

We need to collect all the last digits we get in reverse order, how to do that?
int reversedNumber = reversedNumber * 10 + lastDigit;

Continue above steps in loop  until remaining number is 0.

Note: We may hit integer overflow when we do (reversedNumber * 10 + lastDigit), so make sure before executing that line we check for overflow.

1. reversedNumber * 10 can overflow, so check reversedNumber  > Integer.MAX_VALUE / 10, if yes then (reversedNumber * 10) will surely overflow.

2. reversedNumber * 10 + lastDigit
Adding the + lastDigit can also overflow, if reversedNumber is exactly equal to Integer.MAX_VALUE / 10 then we need to check the + lastDigit we add should be less that 7 (for positive number) because in Java, the integer ranges from -2,147,483,648 to +2,147,483,647 and greater than -8 in case negative number.
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