了解反射的奇怪行为

Question

I was writing this piece of code to understand reflection and encountered one scenario where I couldn't really figure out the reason for the codes' behavior. Hopefully I receive some guidance from the community.
Following is my test model class & here, for every instantiation, I want to know the exact number of instances created during runtime (using reflection)

public final class Model {

    private static final Model instance = new Model("Testing");
    private static int count = 0;

    private String name;

    private Model(String name) {
        this.name = name;
        ++count;
    }

    public static Model getInstance() {
        return instance;
    }

    public static int getInstanceCount() {
        return count;
    }

    public String getName() {
        return name;
    }

    public void doSomething() {
        try {
            System.out.println("Shh.... I am trying to do something");
            Thread.sleep(1000);
            System.out.println("Ok! Done.");
            return;
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
        System.out.println("Oops! I failed in doing your job...");
    }
}

The driver code for this scenario is as follows,

public class ReflectionTest {

    public static void main(String[] args) throws Exception {

        Model.getInstance().doSomething();
        System.out.println(Model.getInstanceCount());

        Constructor<?>[] constructor = Model.class.getDeclaredConstructors();

        for (Constructor<?> aConstructor : constructor) {
            aConstructor.setAccessible(true);
            Model m = (Model) aConstructor.newInstance("Testing through Reflection");
            System.out.println(m.getName());
            m.doSomething();
             System.out.println(m.getInstanceCount());
            //System.out.println(Model.getInstanceCount());
        }
    }
}

The output for this above piece of code came out to be as follows,

Shh.... I am trying to do something
Ok! Done.
0
Testing through Reflection
Shh.... I am trying to do something
Ok! Done.
1

As you can see, the instance count came out to be 1. I expected it to be as 2.
However, I changed the test model class's constructor as shown below. The datatype of count is now changed to Integer, instead of previously set 'int' .

    private Model(String name) {
        this.name = name;
        if (count == null)
            count = 0;
        ++count;
    }

Surprisingly, I get the correct value for the instance count.

Shh.... I am trying to do something
Ok! Done.
1
Testing through Reflection
Shh.... I am trying to do something
Ok! Done.
2

This might be a silly question, but I am not able to ponder on what really happened behind the scenes. I need some guidance from the community on this.
Thanks in advance.

Answer 1

This has nothing to do with reflection.

private static final Model instance = new Model("Testing");
private static int count = 0;

The initializers are executed in order. So:

private static final Model instance = new Model("Testing");

Executing the constructor causes count to be incremented from 0 to 1, but then:

private static int count = 0;

Sets count back to zero.

Reverse the order of the declarations.

private static int count = 0;
private static final Model instance = new Model("Testing");

Or omit the initializer on count (its default value is zero anyway).

private static final Model instance = new Model("Testing");
private static int count;