Summary - Exceptions

Combine try/catch, finally and try expression to write a bank account class.

Summary - Exceptions

In this group you learned to catch errors with try/catch, raise with throw, clean up with finally, use try as an expression and define custom exception classes.

Now it is time to combine them in a small task: define a custom error class, throw it, catch it and finally do cleanup. This is a small sample of a real error-handling flow.

Exercise Build a full flow with a custom error

Define the class MyError(message: String) : Exception(message). Write fun load() that throws MyError("Loading failed"). In main set up try/catch/finally; on error print e.message, and in finally call println("Done").

Show example solution

class MyError(message: String) : Exception(message)

fun load() {
    throw MyError("Loading failed")
}

fun main() {
    try {
        load()
    } catch (e: MyError) {
        println(e.message)
    } finally {
        println("Done")
    }
}

Test yourself

Which is true?
- finally always runs
- throw catches errors
- catch raises errors
- try catches errors
Show answer

finally always runs — finally runs whether or not there is an error.
Match tool to purpose

try

Trial
catch

Catching
finally

Cleanup
throw

Raising

Fill in the blank: write catch

try {
    load()
} ____ (e: MyError) {
    println(e.message)
}

Show answer

try {
    load()
} catch (e: MyError) {
    println(e.message)
}

Next lesson: class

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