"Property must be initialized or be abstract" in init block when throwing an exception

Question

Why does kotlin report Property must be initialized or be abstract. The object construction is never finished, so it should not matter whether a is initialized or not. Could a case be demonstrated where this would be a problem?

class Foo {
    private val a: Int

    init {
        a = 42
        throw Exception()
    }
}

fun main() {
    Foo()
}

kotlin playground

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However these work just fine

fun bar() {
    throw Exception()
}

class Foo {
    private val a: Int

    init {
        a = 42
        bar()
    }
}

fun main() {
    Foo()
}

kotlin playground

class Foo {
    private val a: Int = throw Exception()
}

fun main() {
    Foo()
}

kotlin playground

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Similar java code works as expected:

public class Test {
    private static class Foo {
        private final int a;

        public Foo() throws Exception {
            a = 42;
            throw new Exception();
        }
    }

     public static void main(String []args) throws Exception {
         new Foo();
     }
}

Answer 1

Similar java code works as expected:

Java initializes fields to 0 (or null/false depending on type) by default. You can see it e.g. by printing a's value before the a = 42 line.

Kotlin doesn't, because this implicit initialization makes it too easy to forget to initialize a property and doesn't provide much benefit. So it requires you to initialize all properties which have backing fields.