GWT调用DOM.getElementById时，它不应该导致NullPointerException [英] GWT call to DOM.getElementById not causing a NullPointerException when it should

问题描述

  int x = DOM.getElementById（x ）.getPropertyInt（ 值）; 
 int y = DOM.getElementById（y）。getPropertyInt（value）; 
 int w = DOM.getElementById（w）。getPropertyInt（value）; 
 int h = DOM.getElementById（h）。getPropertyInt（value）; 
  

每次调用 DOM.getElemendById（something）返回 null （我期望我删除它们），但调用 .getPropertyInt（value） on null的返回值不会导致NullPointerException。在开发模式下，我能够逐步浏览所有这些语句，并将x，y，w，h全部分配给零。如果我在调试器中评估Intellij评估器中的这些语句之一，则会抛出NullPointerException。

这对其他人看起来有点疯狂吗？

解决方案

文档说：

 异常：try，catch，finally和用户定义的异常支持为
正常，但Throwable.getStackTrace（）在
生产模式中没有有意义的支持。 
 
注意：由Java VM隐式生成的几个基本异常，大多数
（特别是NullPointerException，StackOverflowError和OutOfMemoryError）在生产模式下不会发生
。相反，JavaScriptException是为
生成的任何隐式生成的异常。这是因为底层
 JavaScript异常的性质无法可靠地映射到适当的Java 
异常类型上。 
  

There is a part of our application that does this...

int x = DOM.getElementById("x").getPropertyInt("value");
int y = DOM.getElementById("y").getPropertyInt("value");
int w = DOM.getElementById("w").getPropertyInt("value");
int h = DOM.getElementById("h").getPropertyInt("value");

Every call to DOM.getElemendById("something") returns null (which I expect as I removed them) but calling .getPropertyInt("value") on that return value of null is not causing a NullPointerException. In dev mode I am able to step through all of these statements and watch x,y,w,h all be assigned to zero. If I evaluate one of these statements in the Intellij evaluator in the debugger there is a NullPointerException thrown.

Doesn't this seem slightly insane to anybody else?

解决方案

The docs say:

Exceptions: try, catch, finally and user-defined exceptions are supported as 
normal, although Throwable.getStackTrace() is not meaningfully supported in 
production mode.

Note: Several fundamental exceptions implicitly produced by the Java VM, most 
notably NullPointerException, StackOverflowError, and OutOfMemoryError, do not 
occur in production mode as such. Instead, a JavaScriptException is produced for 
any implicitly generated exceptions. This is because the nature of the underlying
JavaScript exception cannot be reliably mapped onto the appropriate Java 
exception type.

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