为什么java.util.ArrayList中有OutofBoundsMSSG私有方法？

下面是来自

java.util.ArrayList

的片段：

/**
 * Constructs an IndexOutOfBoundsException detail message.
 * Of the many possible refactorings of the error handling code,
 * this "outlining" performs best with both server and client VMs.
 */
private String outOfBoundsMsg(int index) {
    return "Index: "+index+", Size: "+size;
}

以下是

com.google.collect.premissions

中的片段：

  /*
   * All recent hotspots (as of 2009) *really* like to have the natural code
   *
   * if (guardExpression) {
   *    throw new BadException(messageExpression);
   * }
   *
   * refactored so that messageExpression is moved to a separate
   * String-returning method.
   *
   * if (guardExpression) {
   *    throw new BadException(badMsg(...));
   * }
   *
   * The alternative natural refactorings into void or Exception-returning
   * methods are much slower.  This is a big deal - we're talking factors of
   * 2-8 in microbenchmarks, not just 10-20%.  (This is a hotspot optimizer
   * bug, which should be fixed, but that's a separate, big project).
   *
   * The coding pattern above is heavily used in java.util, e.g. in ArrayList.
   * There is a RangeCheckMicroBenchmark in the JDK that was used to test this.

请有人解释一下：

---

• 为什么需要私密的

  OutofboundsMSSG

• “此大纲显示的效果最好…”的含义
• 我应该开始重构代码，为异常构造函数包含字符串返回方法吗

“此大纲显示的效果最好…”的含义

它与内联相反，但不是一个标准术语，这就是它被引用的原因

为什么需要专用OutofBoundsMSSG

这就是“大纲”将代码提取到一个单独的方法的意义

我应该开始重构代码，为异常构造函数包含字符串返回方法吗

---

如果您关心每次抛出没有消息字符串文本的异常时浪费的3纳秒，那么是的。换句话说：没有。

OutofBoundsMSSG

不是“必需的”，Java开发人员（显然还有Google Collections）发现这对他们的库来说是一个足够的性能改进（可能是在仔细测试之后）。这也是一种优化，可能不适用于所有Java版本和实现。