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Thread: will the result always be true?

  1. #1
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    Question will the result always be true?

    public class Main {
    public static void main(String[] args) {
    A a =null;
    try{
    a = new A(1);
    }catch (IOException e) {
    System.out.println(a == null);
    }

    }
    }

    class A {
    private int v;
    public A(int val) throws IOException {
    v= val;
    throw new IOException("123");
    }
    }

    as far as i know
    the process of new a object has 3 steps:
    1. allocate memory
    2. execute construct function
    3. assign to reference

    due to instruction reordering of JIT, the process may be changed to 1->3->2 rather than 1->2->3.
    so will the result of the code above always be true?

    sorry for my english
    Last edited by aclliceon; April 23rd, 2024 at 06:31 AM.

  2. #2
    Member John Joe's Avatar
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    Default Re: will the result always be true?

    Why don't you try to run using IDE?
    Whatever you are, be a good one

  3. #3
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    Default Re: will the result always be true?

    Yes, the result of the code will always be true. In simpler terms, when the program tries to create a new object of class A, it runs into an issue because the constructor for class A throws an error (IOException). When an error happens during the creation of an object, the object isn't created, so the reference "a" remains as null. Therefore, when the program checks if "a" is null inside the catch block, it will always be true. If you need help with programming assignments or understanding concepts like this, you can check out https://www.programminghomeworkhelp.com/. They specialize in offering top-notch assistance in a wide range of programming languages, with a team of experts proficient in various coding languages, ensuring that students receive the best support for their programming assignments, homework, and projects.

  4. #4
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    Default Re: will the result always be true?

    Your understanding of the steps involved in creating a new object in Java is correct. However, due to the way JIT (Just-In-Time) compiler optimizations and instruction reordering work, there's a possibility that step 3 (assigning the reference) might happen before step 2 (executing the constructor).

    In the provided code, if an IOException is thrown during the construction of object 'a', the reference 'a' will remain null. Depending on the timing of instruction reordering, it's possible that the comparison `System.out.println(a == null)` might evaluate to true, even though it seems counterintuitive.

    However, to ensure a more predictable behavior, you could avoid relying on the potential reordering by moving the comparison inside the try block, like so:

    ```java
    public class Main {
    public static void main(String[] args) {
    A a = null;
    try {
    a = new A(1);
    System.out.println(a == null);
    } catch (IOException e) {
    System.out.println(a == null);
    }
    }
    }

    class A {
    private int v;

    public A(int val) throws IOException {
    v = val;
    throw new IOException("123");
    }
    }
    ```

    By doing this, you guarantee that the comparison `System.out.println(a == null)` is performed after the object 'a' has been initialized or remains null due to the exception.

    To ensure a more predictable behavior, you could avoid relying on the potential reordering by moving the comparison inside the try block, as demonstrated. This adjustment ensures that the comparison System.out.println(a == null) is performed after the object 'a' has been initialized or remains null due to the exception. If you need further help with Java assignment, there are many resources available online where you can seek guidance and support like ProgrammingHomeworkHelp.com.

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