blocks|key|1878070|text|表达式不是按照您所想的方式进行解析的。不是这样的|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1878071|(test1=false)+%7C%7C+(test1+==+false)|code-block|syntax|javascript|1878072|在这种情况下，结果应该是true，但是|offset|length|style|CODE|1878073|test1+=+(false+%7C%7C+test1+==+false)|1878074|首先计算false+%7C%7C+test1+==+false表达式的值，该值为false，因为在计算过程中将test1设置为true。|1878075|这样解析它的原因是%7C%7C的precedence低于==运算符，但高于赋值运算符=的优先级。|1878076|entityMap|0|LINK|mutability|MUTABLE|url|http://introcs.cs.princeton.edu/java/11precedence/^0|0|0|C|4|0|0|4|N|10|5|1F|5|1N|4|0|9|2|O|2|12|1|C|A|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@$I|13|J|14|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|16|8|@$I|17|J|18|K|L]|$I|19|J|1A|K|L]|$I|1B|J|1C|K|L]|$I|1D|J|1E|K|L]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1F|8|@$I|1G|J|1H|K|L]|$I|1I|J|1J|K|L]|$I|1K|J|1L|K|L]]|9|@$I|1M|J|1N|1|1O]]|A|$]]|$1|S|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|Z]]]]

The expression is not parsed the way you think. It's not

<pre><code>(test1=false) || (test1 == false)
</code></pre>

in which case the result would have been <code>true</code>, but

<pre><code>test1 = (false || test1 == false)
</code></pre>

The value of <code>false || test1 == false</code> expression is computed first, and it is <code>false</code>, because <code>test1</code> is set to <code>true</code> going into the computation.

The reason it is parsed this way is that the <a href="http://introcs.cs.princeton.edu/java/11precedence/">precedence</a> of the <code>||</code> is lower than that of the <code>==</code> operator, but higher than the precedence of the assignment operator <code>=</code>.

blocks|key|1878110|text|基本上，这是一个优先级问题。你假设你的代码等同于：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1878111|if+((test1+=+false)+%7C%7C+(test1+==+false))|code-block|syntax|javascript|1878112|..。但事实并非如此。它实际上相当于：|1878113|if+(test1+=+(false+%7C%7C+test1+==+false))|1878114|..。相当于：|1878115|if+(test1+=+(false+%7C%7C+false))|1878116|(因为test1从一开始就是true+)|offset|length|style|CODE|1878117|1878118|if+(test1+=+false)|1878119|它将值false赋值给test1，表达式的结果为false。|1878120|有关运算符优先级的有用表格，请参阅Java+tutorial+on+operators。|1878121|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html^0|0|0|0|0|0|0|3|5|E|4|0|0|0|3|5|B|5|O|5|0|H|Q|0|0^^$0|@$1|2|3|4|5|6|7|19|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1A|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1B|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|1C|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|1D|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|1E|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|1F|8|@$Q|1G|R|1H|S|T]|$Q|1I|R|1J|S|T]]|9|@]|A|$]]|$1|U|3|L|5|6|7|1K|8|@]|9|@]|A|$]]|$1|V|3|W|5|D|7|1L|8|@]|9|@]|A|$E|F]]|$1|X|3|Y|5|6|7|1M|8|@$Q|1N|R|1O|S|T]|$Q|1P|R|1Q|S|T]|$Q|1R|R|1S|S|T]]|9|@]|A|$]]|$1|Z|3|10|5|6|7|1T|8|@]|9|@$Q|1U|R|1V|1|1W]]|A|$]]|$1|11|3|-4|5|6|7|1X|8|@]|9|@]|A|$]]]|12|$13|$5|14|15|16|A|$17|18]]]]

This is a precedence issue, basically. You're assuming that your code is equivalent to:

<pre><code>if ((test1 = false) || (test1 == false))
</code></pre>

... but it's not. It's actually equivalent to:

<pre><code>if (test1 = (false || test1 == false))
</code></pre>

... which is equivalent to:

<pre><code>if (test1 = (false || false))
</code></pre>

(because <code>test1</code> is <code>true</code> to start with)

... which is equivalent to:

<pre><code>if (test1 = false)
</code></pre>

which assigns the value <code>false</code> to <code>test1</code>, with the result of the expression being <code>false</code>.

See the <a href="https://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html" rel="noreferrer">Java tutorial on operators</a> for a useful table of operator precedence.

blocks|key|1878144|text|(test1+=+false+%7C%7C+test1+==+false)返回false，因为它们都是false。(test1+=+false+%7C%7C+test1+==+true)这是真，因为它们中有一个是真的|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1878145|entityMap^0|0|X|1H|W|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

<code>(test1 = false || test1 == false)</code> returns false, because both of them are false.<code>(test1 = false || test1 == true)</code> this is true because one of them is true

How does a Java if statement work when it has an assignment and an equality check <code>OR</code>-d together??

<pre><code>public static void test() {
 boolean test1 = true; 
 if (test1 = false || test1 == false) {
 System.out.println("TRUE");
 } else {
 System.out.println("FALSE");
 } 
}
</code></pre>

Why is this printing FALSE?

Why does this if statement, with an assignment and equality check, evaluate to false?

Java

当Java if语句同时具有赋值和相等检查OR-d时，它是如何工作的？public static void test() {    boolean test1 = true;     if (test1 = false || test1 == false) {        System.out.println("TR...

问为什么这条带有赋值和相等检查的if语句的计算结果为false？
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问为什么这条带有赋值和相等检查的if语句的计算结果为false？
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