Custom Exceptions क्या हैं

एक custom exception आपकी अपनी नामित तरह की error है, ताकि आपका program बिल्कुल बता सके कि आपके अपने शब्दों में क्या गलत हुआ।

In this page:

Declaring a Custom Exception
Adding Extra Properties
Building a Hierarchy of Custom Exceptions
Including a Cause

Syntax

kotlin

class CustomException(message: String) : Exception(message)

class DetailedException(val field: Type, message: String) : Exception(message)

throw CustomException("message")

Declaring a Custom Exception

एक custom exception class Exception (या इसकी एक subclass) को extend करती है, आमतौर पर एक message को superclass constructor को forward करते हुए ताकि इसे किसी भी built-in exception की तरह print और inspect किया जा सके।

उदाहरण: Declaring a Custom Exception

markup

// Define a class `InsufficientFundsException`
class InsufficientFundsException(message: String) : Exception(message)

// Define the function `withdraw` taking `balance`, `amount` and returning a Double
fun withdraw(balance: Double, amount: Double): Double {
    if (amount > balance) throw InsufficientFundsException("Cannot withdraw $amount from balance $balance")
    // Return `balance - amount` from this function
    return balance - amount
}

// Entry point: execution of the program starts here
fun main() {
    try {
        withdraw(100.0, 150.0)
    } catch (e: InsufficientFundsException) {
        // Print "Error: ${e.message}" to the console, with a trailing newline
        println("Error: ${e.message}")
    }
}

Adding Extra Properties

एक custom exception एक message से आगे अतिरिक्त properties रख सकता है, catching code को सिर्फ text parse करने के बजाय programmatically काम करने के लिए structured जानकारी देते हुए।

उदाहरण: Adding Extra Properties

markup

// Define a class `ValidationException`
class ValidationException(val field: String, message: String) : Exception(message)

// Define the function `validateAge` taking `age`
fun validateAge(age: Int) {
    if (age < 0) throw ValidationException("age", "Age cannot be negative")
}

// Entry point: execution of the program starts here
fun main() {
    try {
        validateAge(-5)
    } catch (e: ValidationException) {
        // Print "Invalid field ${e.field}: ${e.message}" to the console, with a trailing newline
        println("Invalid field ${e.field}: ${e.message}")
    }
}

Building a Hierarchy of Custom Exceptions

संबंधित custom exceptions एक common open base class share कर सकते हैं, calling code को यह उसकी ज़रूरी precision के आधार पर एक specific exception type या ज़्यादा general base type catch करने देते हुए।

उदाहरण: Building a Hierarchy of Custom Exceptions

markup

open class AppException(message: String) : Exception(message)
// Define a class `NetworkException`
class NetworkException(message: String) : AppException(message)
// Define a class `DatabaseException`
class DatabaseException(message: String) : AppException(message)

// Entry point: execution of the program starts here
fun main() {
    // Declare a read-only variable `errors`, set to `listOf(NetworkException("Timeout"), DatabaseException("Connection lost"))`
    val errors = listOf(NetworkException("Timeout"), DatabaseException("Connection lost"))
    // Loop over `errors`, binding each item to `error`
    for (error in errors) {
        try {
            throw error
        } catch (e: AppException) {
            // Print "App error: ${e.message}" to the console, with a trailing newline
            println("App error: ${e.message}")
        }
    }
}

Including a Cause

किसी custom exception का constructor एक cause (एक दूसरा Throwable) भी accept और forward कर सकता है, callers को एक साफ़, ज़्यादा उच्च-स्तरीय exception दिखाते हुए original underlying error को संरक्षित रखते हुए।

उदाहरण: Including a Cause

markup

// Define a class `DataLoadException`
class DataLoadException(message: String, cause: Throwable) : Exception(message, cause)

// Entry point: execution of the program starts here
fun main() {
    try {
        try {
            throw NumberFormatException("bad number")
        } catch (e: NumberFormatException) {
            throw DataLoadException("Failed to load data", e)
        }
    } catch (e: DataLoadException) {
        // Print "${e.message}, caused by: ${e.cause?.message}" to the console, with a trailing newline
        println("${e.message}, caused by: ${e.cause?.message}")
    }
}

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Custom Exceptions क्या हैं

Declaring a Custom Exception

Adding Extra Properties

Building a Hierarchy of Custom Exceptions

Including a Cause

Chapter Quiz — Complete all 6 topics to unlock

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