Java 三元（立即如果）评估
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Java ternary (immediate if) evaluation
提问by Mike Pone
I can't find the relevant portion of the spec to answer this. In a conditional operator statement in Java, are both the true and false arguments evaluated?
我找不到规范的相关部分来回答这个问题。在 Java 中的条件运算符语句中，是否同时评估了 true 和 false 参数？
So could the following throw a NullPointerException
那么以下内容是否会抛出 NullPointerException
Integer test = null;
test != null ? test.intValue() : 0;
采纳答案by Michael Myers
Since you wanted the spec, here it is (from §15.25 Conditional Operator ? :, the last sentence of the section):
由于您想要规范，这里是（来自§15.25 Conditional Operator ? :，本节的最后一句）：
The operand expression not chosen is not evaluated for that particular evaluation of the conditional expression.
对于条件表达式的特定评估，不会评估未选择的操作数表达式。
回答by stevedbrown
No, it couldn't. That's the same as:
不，不能。这与：
Integer test = null;
if ( test != null ) {
test = test.intValue();
}
else {
test = 0;
}
回答by Micha? Króliczek
I know it is old post, but look at very similar case and then vote me :P
我知道这是旧帖子，但请查看非常相似的案例，然后投票给我：P
Answering original question : only one operand is evaluated BUT:
回答原始问题：仅评估一个操作数，但：
@Test
public void test()
{
Integer A = null;
Integer B = null;
Integer chosenInteger = A != null ? A.intValue() : B;
}
This test will throw NullPointerExceptionalways and in this case IF statemat is not equivalent to ?: operator.
此测试将NullPointerException始终抛出，在这种情况下，IF statemat 不等同于 ?: 运算符。
The reason is here http://docs.oracle.com/javase/specs/jls/se5.0/html/expressions.html#15.25. The part about boxing/unboxing is embroiled, but it can be easy understood looking at:
原因在这里http://docs.oracle.com/javase/specs/jls/se5.0/html/expressions.html#15.25。关于装箱/拆箱的部分被卷入其中，但看一下就很容易理解：
"If one of the second and third operands is of type
booleanand the type of the other is of typeBoolean, then the type of the conditional expression isboolean."
“如果第二个和第三个操作数之一是 type
boolean而另一个的类型是 typeBoolean，则条件表达式的类型是boolean。”
The same applies to Integer.intValue()
这同样适用于 Integer.intValue()
Best regards!
此致！
