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I want a algorithm kind of thing which generates random unique number based on the digits of the input number. I found one solution.
How to Generate an unique ID in Java
SCJP 1. There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors. Forum: Java in General. Hi, I am developing a application, which has some int manipulations. Thing is i am getting input values as, etc. I need it very urgent. James Sabre. I like One possibility - create a map between the numbers and an int. Start the int values at 0 and increment each time you add a big number.
Why not! They are numbers and they are unique. There is obviously more to your requirement then you have said. Hunter McMillen. As long as you increment every time you add you will always have a unique id. Database' often use this scheme for IDs Hunter. Since you already have a database then why not just use a database table mapping the big integers to the small integers. You can use auto-increment when inserting the big numbers. How can it be? You cannot make any simple manipulations of a big number that will create a unique int!
Rob Spoor. There is absolutely no way you can get an algorithm that guarantees uniqueness.
Eventually you will get a duplicate. That said, the auto-increment from 0 or 1, as databases do is going to be as good as it gets, as long as you have proper synchronization. In practice you'll run out of memory long before that happens with this solution. Can i suggest we back up? What are the possible input values? It is not clear to me on my scanning this thread what the allowable inputs are.
Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Create a UUID. Edit: Alternative suggested in the comments - this relies on under-the-hood "magic" for thread safety, but is more scalable and just as safe:.
UUID : toString method. Here's my two cent's worth: I've previously implemented an IdFactory class that created IDs in the format [host name]-[application start time]-[current time]-[discriminator]. Here's the code in case it's of any use:. This adds a bit more randomness to the UUID generation but ensures each generated id is the same length. IMHO aperkins provided an an elegant solution cause is native and use less code.
But if you need a shorter ID you can use this approach to reduce the generated String length:. This will generate the random uniqueID whose return type will be String. Learn more. How do I create a unique ID in Java? Asked 10 years, 7 months ago. Active 2 years, 3 months ago. Viewed k times.Generate unique id value for dynamically created form controls in angular
I'm looking for the best way to create a unique ID as a String in Java. Any guidance appreciated, thanks. I should mention I'm using Java 5. Supertux Supertux 6, 10 10 gold badges 38 38 silver badges 46 46 bronze badges. Take a look at this stackoverflow. Active Oldest Votes. BalusC k gold badges silver badges bronze badges. It's not all that human readable tho And making it human-readable usually makes it longer which in turn makes it less human-readable.
I wasn't aware he wanted a human readable unique ID Another note - if you only need application uniqueness, and AtomicInteger as noted by Michael Borgwardt is a much better option, but if you need global uniqueness, a UUID is a much better bet. Why can't we use System. Michael Borgwardt Michael Borgwardt k 71 71 gold badges silver badges bronze badges. Also, UUID. Adamski: this method will only create unique values as long as you don't restart the JVM, have only 1 JVM running and as long as the counter doesn't overflow.
All those assumptions can easily be broken. And if you need global uniqueness, it is the easiest way to achieve that. However, if you only need local uniqueness i.
Mitch Wheat Mitch Wheat k 38 38 gold badges silver badges bronze badges. Adamski Adamski This adds a bit more randomness to the UUID generation but ensures each generated id is the same length import org.
DigestUtils; import java.I was recently working on an application that had a sharded MySQL database. While working on this application, I needed to generate unique IDs that could be used as the primary keys in the tables.
So I looked at various existing solutions for this, and finally wrote a simple bit unique ID generator that was inspired by a similar service by Twitter called Twitter snowflake. UUIDs are bit hexadecimal numbers that are globally unique. The chances of the same UUID getting generated twice is negligible. When your dataset increases, the index size increases as well and the query performance takes a hit. This is smaller than the earlier bit UUID.
But again the size is relatively longer than what we normally have in a single MySQL auto-increment field a bit bigint value. This approach uses a centralized database server to generate unique incrementing IDs. This approach is used by Flickr.
The problem with this approach is that the ticket server can become a write bottleneck. Moreover, you introduce one more component in your infrastructure that you need to manage and scale.
Twitter snowflake is a dedicated network service for generating bit unique IDs at high scale. The IDs generated by this service are roughly time sortable. The extra 1 bit is reserved for future purposes. Since the IDs use timestamp as the first component, they are time sortable.
The IDs generated by twitter snowflake fits in bits and are time sortable, which is great. Finally, I wrote a simple sequence generator that generates bit IDs based on the concepts outlined in the Twitter snowflake service. Your microservices can use this Sequence Generator to generate IDs independently.
This is efficient and fits in the size of a bigint. You can also supply a NodeID to the sequence generator. That will guarantee uniqueness. The epoch timestamp for this particular time is Now, the first 41 bits of the ID after the signed bit will be filled with the epoch timestamp.
Next, we take the configured node ID and fill the next 10 bits with the node ID. Finally, we fill the last 12 bits with the local counter. UUID Universally unique identifier.Mohini Dhanaskar wrote: Sir, after running the same code. Getting an error. ServletException: Servlet. NullPointerException at ComplaintServlet. Mohini Dhanaskar wrote: Sir, Should i make any change in the coding also or what? If this ID is related to a database table, then I would strongly urge you to use a sequence number obtained from the DB itself.
Forum: Beginning Java. Automatically Generating ID. Mohini Dhanaskar.
Prashant Chindhade. Suppose this is my code for Complaint Registration, then where should i put that code.
You can put this code anywhere see for your edited servlet. Sir, after running the same code. Still showing an compile time error.
Is it showing this error after appending my code? HttpServletRequest; import javax.
HttpServletResponse; import javax. Check this Link it will show you basic steps to connect to database. Also check this. Winston Gutkowski. I likeHashids is a small open-source library that generates short, unique, non-sequential ids from numbers. You can also decode those ids back. This is useful in bundling several parameters into one or simply using them as short UIDs.
That's where Hashids uses a variation of Fisher-Yates algorithm :. The code above might look complicated, but it does one simple thing — shuffles the alphabet based on user's salt. You can see that the shuffle is pretty good even when salt value is not that much different. This is what makes the base of Hashids work. Now we are able to encode one integer based on the salt value the user provides.
But Hashids is able to encode several integers into one id. This is done by reserving a few characters from the alphabet as separators. These characters are not used in encoding, but instead do the job of purely separating the real encoded values.
Let's say we encoded 1, 2, 3 without the salt and got "o2fXhV". Actual values in this output are highlighted: o 2 f X h V. Letters "f" and "h" are simply used as separators. Letter "o" in this case is reserved for another type of job - it acts as a lottery character to randomize incremental input. If we encode numbers as we increment them, the output is somewhat predictable:.
Online GUID Generator
Code Review Stack Exchange is a question and answer site for peer programmer code reviews. It only takes a minute to sign up. I need to generate a 64 bit unique integer in Java.
I need to make sure that there is very few or no collisions if possible. In this case, there's no need for anything more complicated than atomically incrementing a counter:. To offer a more specific critique of your code, it's unnecessarily complicated and inefficient. I don't see anything incorrect about it i. Here, I suggest you do while true instead of for. It is a matter of preference, but I think while true is easier to understand. Also, always put braces for if statements.
If you don't, horrible bugs may occur. Here is an example:. Now you have a horrible bug. It looks fine, but when you run it, doSomethingElse will execute no matter what isSomething returns. If you actually had braces:. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Generating a 64 bit unique integer in Java Ask Question.
Asked 5 years, 2 months ago. Active 5 years, 2 months ago. Viewed 8k times. If it is random, then that is also fine.
Active Oldest Votes. Pierre Menard Pierre Menard 1, 9 9 silver badges 25 25 bronze badges.When you generate random numbers it's often the case that each generated number number must be unique.
A good example is picking lottery numbers. Each number picked randomly from a range e. The easiest way to pick unique random numbers is to put the range of numbers into a collection called an ArrayList.
If you've not come across an ArrayList before, it's a way of storing a set of elements that don't have a fixed number. The elements are objects that can be added to or removed from the list. For example, let's make the lottery number picker. It needs to pick unique numbers from a range of 1 to First, put the numbers into an ArrayList using the add method.
It takes the object to be added as a parameter:. Note that we are using the Integer wrapper class for the element type so that the ArrayList contains objects and not primitive data types. A utility class called Collections offers different actions that can be performed on a collection like an ArrayList e. One of the actions it can perform is to shuffle the elements. The shuffle will randomly move each element to a different position in the list. It does this by using a Random object.
This means it's a deterministic randomness, but it will do in most situations.
How to Generate an unique ID in Java
To shuffle the ArrayList, add the Collections import to the top of the program and then use the Shuffle static method. It takes the ArrayList to be shuffled as a parameter:. To pick the unique random numbers simply read the ArrayList elements one by one by using the get method. It takes the position of the element in the ArrayList as a parameter. For example, if the lottery program needs to pick six numbers from the range of 1 to Share Flipboard Email. Paul Leahy. Computer Science Expert.
Paul Leahy is a computer programmer with over a decade of experience working in the IT industry, as both an in-house and vendor-based developer. Updated February 05, The output shows the range of numbers from 1 to 40 in order:. Collections; import java.