在尝试向泛型集合(本例中为List)添加错误类型的元素时，清单2中的程序会生成编译时错误消息。

Listing 2 contains a program that generates the compilation-time error message that happens when you try to add the wrong type of element to a generic collection - a List in this case.

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但是JIT编译器具有一个有限的编译时预算，而且会影响程序的运行时性能。

But JIT compilers have only a limited compile-time budget and can impact the program's run-time performance.

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当s DO的类型在编译阶段未知时，或者当程序部署完以后可能要添加新的属性时，这特别有用。

This is particularly useful when the type of the SDO is not known at compile time, or when new properties might be added after the program is deployed.

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