try-finally块可防止StackOverflowError [英] Try-finally block prevents StackOverflowError

问题描述

看看以下两种方法:

public static void foo() {
    try {
        foo();
    } finally {
        foo();
    }
}

public static void bar() {
    bar();
}

---

运行bar()显然会导致StackOverflowError，但是运行foo()不会(程序似乎无限期地运行). 那是为什么?

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Running bar() clearly results in a StackOverflowError, but running foo() does not (the program just seems to run indefinitely). Why is that?

推荐答案

它不会永远运行.每次堆栈溢出都会导致代码移至finally块.问题在于这将需要非常，非常长的时间.时间顺序为O(2 ^ N)，其中N是最大堆栈深度.

It doesn't run forever. Each stack overflow causes the code to move to the finally block. The problem is that it will take a really, really long time. The order of time is O(2^N) where N is the maximum stack depth.

想象最大深度为5

foo() calls
    foo() calls
       foo() calls
           foo() calls
              foo() which fails to call foo()
           finally calls
              foo() which fails to call foo()
       finally
           foo() calls
              foo() which fails to call foo()
           finally calls
              foo() which fails to call foo()
    finally calls
       foo() calls
           foo() calls
              foo() which fails to call foo()
           finally calls
              foo() which fails to call foo()
       finally
           foo() calls
              foo() which fails to call foo()
           finally calls
              foo() which fails to call foo()
finally calls
    foo() calls
       foo() calls
           foo() calls
              foo() which fails to call foo()
           finally calls
              foo() which fails to call foo()
       finally
           foo() calls
              foo() which fails to call foo()
           finally calls
              foo() which fails to call foo()
    finally calls
       foo() calls
           foo() calls
              foo() which fails to call foo()
           finally calls
              foo() which fails to call foo()
       finally
           foo() calls
              foo() which fails to call foo()
           finally calls
              foo() which fails to call foo()

要使每个级别进入finally块，所需的时间是堆栈深度的两倍 10,000或更多.如果您每秒可以进行10,000,000次呼叫，那么这将花费10 ^ 3003秒，甚至比宇宙的时间还要长.

To work each level into the finally block take twice as long an the stack depth could be 10,000 or more. If you can make 10,000,000 calls per second, this will take 10^3003 seconds or longer than the age of the universe.

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