How to Get a Substring in Kotlin Until a Specific Character

Описание: Learn how to efficiently extract a substring from a string in Kotlin by focusing on specific characters. This guide details the process of retrieving a decimal number formatted to two decimal places.
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This video is based on the question https://stackoverflow.com/q/63861397/ asked by the user 'GeoCap' ( https://stackoverflow.com/u/13347175/ ) and on the answer https://stackoverflow.com/a/63861442/ provided by the user 'nt95' ( https://stackoverflow.com/u/11202401/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Get a Substring in Kotlin Until a Specific Character: A Step-by-Step Guide

Working with strings is a common task in programming, and Kotlin provides powerful tools for string manipulation. If you find yourself needing to extract specific parts of a string—particularly when dealing with numbers formatted as strings—you’re in the right place! In this guide, we will address a common scenario: extracting a substring from a string that follows a specific pattern. Let's dive in!

The Problem: Extracting a Decimal Number from a String

Imagine you have a string formatted like this: XXXXXXX30.00000. Here, the first seven characters (XXXXXXX) are not needed, and we want to extract the decimal number 30.00, which follows the first part of the string. The main requirements are:

Start reading from index 7 to the decimal point.

Format the result to two decimal places.

Ensure that the output remains a string, not a number.

The Solution: Step-by-Step Guide

Let’s break down how to solve this problem effectively in Kotlin.

Step 1: Remove Unwanted Characters

The first step is to eliminate the first seven characters from the string. We can achieve this by using the removeRange() function. Here’s how it looks in code:

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What this does: The removeRange(0, 7) method removes characters from index 0 to 6, leaving us with the substring that starts from the decimal number.

Step 2: Convert to Number

Once we have the newString, the next step is to convert it to a number type. If you are sure that the string will always represent a valid number, you can convert it directly to a double:

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Caution: If there is any possibility that the string may not be a valid number, it’s wise to use exception handling to avoid crashes in your application.

Step 3: Handle Conversion Safely

To safely handle the conversion, we can use a try-catch block. Here’s how that would look:

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What this does: The try-catch block will catch any exceptions thrown when attempting to convert newString to a double. This protects your application from runtime errors.

Step 4: Format to Two Decimal Places

Finally, to ensure that our number is formatted to two decimal places as a string, we can use the String.format() function. Here’s how to implement that:

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Result: This will format yourNumber to a string retaining only two decimal places.

Summary

By following these clear steps, you can easily manipulate strings in Kotlin to extract the desired part of a string while ensuring the result is formatted precisely as needed. Here’s a quick recap:

Use removeRange to discard unwanted characters.

Convert the substring to a double safely with a try-catch block.

Format the number to two decimal places using String.format().

With this guide, you should now have a solid understanding of how to extract and format substrings in Kotlin, tailored specifically to your needs. Happy coding!