The answer is to provide a more useful type of exception that also contains a lower-level exception. Listing 1 shows a simple ApplicationException that does just this

答案是提供一类更有用的异常，它还包含低级异常。

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Friday USES level 2 and since Thursday USES level 1, a lower level, RMAN will backup changes since Thursday.

星期五使用级别2，由于星期四使用级别1——较低的级别，所以RMAN将备份星期四以后的更改。

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In a typical software system, function calls flow downward from higher-level components to lower-level ones; whereas events percolate up in the opposite direction. Figure 1 illustrates this pattern.

在典型的软件系统中，函数的调用流是从较高级部分到低级部分进行的；而事件是以相反的方向过滤的，如Figure 1所示。

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But then the market pulled back again to a level lower than the May 1 peak.

FORBES: Fiscal Cliff Could Be One Mean Grinch For Stocks

Support for this pair seems solid around 1.4950 to 1.4960, but a break lower could easily test the 1.4860 level.

FORBES: Dollar Slips As Pound, Euro And Canadian Dollar Gain

The report showed a deeper consumer-retrenchment than was expected with sales sliding by 1.1% between months leaving the level 1.9% lower than a year ago.

FORBES: Lingering Fear Floats The Dollar