Скачать или смотреть How to Generate Random Numbers of Specific Digits in Java

A step-by-step guide on how to generate random numbers in Java with specific requirements. Learn to create a string of random digits starting with 1-9 followed by two digits from 10-99!
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This video is based on the question https://stackoverflow.com/q/66435723/ asked by the user 'Pratik Chauhan' ( https://stackoverflow.com/u/14863514/ ) and on the answer https://stackoverflow.com/a/66436066/ provided by the user 'Dan Baruch' ( https://stackoverflow.com/u/8688810/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Generate Random Numbers of Specific Digits in Java

Generating random numbers is a common necessity in programming, especially when dealing with unique IDs, quiz apps, or game scores. If you're learning Java or Android development, you might want to know how to generate random numbers following a specific format: a single-digit number from 1-9 followed by two random digits from 10-99. In this guide, we will explore how to accomplish this easily and efficiently.

The Problem

Imagine you need to create a string of random numbers that meets the following criteria:

The first digit should be a number from 1 to 9 (inclusive).

The next two digits should each be a number from 10 to 99 (inclusive).

For instance, valid outputs would be 123, 741, or 156. However, outputs such as 045 or 0 as the second digit would not be acceptable because they don't meet the criteria.

The Solution

Here's how to generate such random numbers in Java using the Random class. We will discuss the steps in detail.

Step 1: Setting Up Your Random Number Generator

First, you will need to create an instance of the Random class. This instance will help you to generate the required random numbers.

[[See Video to Reveal this Text or Code Snippet]]

This line of code creates a new Random object that allows us to generate random integers.

Step 2: Generating the Random Digits

Next, you need to generate the three random digits according to the specified ranges:

[[See Video to Reveal this Text or Code Snippet]]

ran1 uses nextInt(9) + 1 to ensure the range is from 1 to 9.

ran2 uses nextInt(90) + 10 to generate numbers strictly between 10 and 99.

Step 3: Combining the Generated Digits into a String

Now, you have two separate integers, but you want to display them as a single string. You have two options here:

Option 1: Concatenation

This first option involves converting each number to a string and then concatenating them:

[[See Video to Reveal this Text or Code Snippet]]

While this method works, it may not be the most efficient.

Option 2: Mathematical Combination

Alternatively, you can combine them mathematically:

[[See Video to Reveal this Text or Code Snippet]]

In this method:

ran1 * 100 shifts the first digit to the hundreds place.

Adding ran2 ensures that both digits are in the string.

Conclusion

Using the Java Random class, generating a string of random numbers with specific digit conditions can be easily achieved by following the steps we discussed. Whether you prefer the concatenation of strings or the mathematical approach, you now have the tools needed to generate random numbers programmatically.

This technique can be used in various applications, from games to inventory systems, ensuring unique and valid numeric identifiers every time. Happy coding!