Java中的fibonacci函数的尾调用优化

public class Fibonacci {
    public static void main(String[] args) throws InterruptedException {
        int n = Integer.parseInt(args[0]);
        System.out.println("n Value of n : " + n);
        System.out.println("n Using Iteration : ");
        long l1 = System.nanoTime();
        fibonacciIterative(n);
        long l2 = System.nanoTime();
        System.out.println("iterative time = " + (l2 - l1));
        System.out.println(fibonacciIterative(n));

        System.out.println("n Using Tail recursion : ");
        long l3 = System.nanoTime();
        fibonacciTail(n);
        long l4 = System.nanoTime();
        System.out.println("Tail recursive time = " + (l4 - l3));
        System.out.println(fibonacciTail(n));

        System.out.println("n Using Recursion : ");
        long l5 = System.nanoTime();
        fibonacciRecursive(n);
        long l6 = System.nanoTime();
        System.out.println("Head recursive time = " + (l6 - l5));
    }

    private static long fibonacciRecursive(int num) {
        if (num == 0) {
            return 0L;
        }
        if (num == 1) {
            return 1L;
        }
        return fibonacciRecursive(num - 1) + fibonacciRecursive(num - 2);
    }

    private static long fibonacciIterative(int n) throws InterruptedException {
        long[] arr = new long[n + 1];
        arr[0] = 0;
        arr[1] = 1;
        for (int i = 2; i <= n; i++) {
            // Thread.sleep(1);
            arr[i] = arr[i - 1] + arr[i - 2];
        }
        return arr[n];
    }

    private static long fibonacciTail(int n) {
        if (n == 0)
            return 0;
        return fibHelper(n,1,1);
    }

    private static long fibHelper(int n,int m,long fibM_minus_one,long fibM) {
        if (n == m)
            return fibM;
        return fibHelper(n,m + 1,fibM,fibM_minus_one + fibM);
    }
}

在运行这个程序时,我提出了一些结果：

>头部递归方法在n> 50时不能完成.程序看起来像挂了.任何想法,为什么会发生这种情况？
与Head递归相比,尾递归方法花费的时间要少得多.有时比迭代方法花费更少的时间.这是否意味着java在内部执行一些尾部调用优化？
如果是这样,为什么我会在n>下给StackOverflowError 5000？

系统规格：

英特尔核心5处理器,

Windows XP,

32位Java 1.6

JVM的默认堆栈大小.