Print Numbers - Multithreaded Alternating Number Printer

Question

## Problem

You have two threads: `EvenThread` prints even numbers and `OddThread` prints odd numbers. They must coordinate to print numbers in order from 1 to `n`: `1, 2, 3, 4, ...`

Implement the synchronization mechanism.

```java
class NumberPrinter {
    private int n;
    public NumberPrinter(int n) { this.n = n; }
    public void printEven(Runnable printNumber) throws InterruptedException {}
    public void printOdd(Runnable printNumber) throws InterruptedException {}
}
```

`printNumber.run()` prints the current number. The two methods will be called from separate threads simultaneously. You must not busy-wait.

## Example

```
n = 5
Expected output (in order): 1 2 3 4 5
```

## Follow-ups

1. How does your solution change if there are three threads: one for multiples of 3, one for multiples of 2 (but not 3), one for the rest?
2. What is the difference between using `wait/notify`, `Semaphore`, and `ReentrantLock` with `Condition` here?
3. What happens if `printNumber.run()` throws an exception mid-run?
4. Demonstrate a scenario where your implementation could deadlock, and how you avoid it.

Print Numbers - Multithreaded Alternating Number Printer

Question Details

Full Details

Topics

More from Google