为什么带有赋值和等式检查的if语句的计算结果为false？ [英] Why does this if statement, with an assignment and equality check, evaluate to false?

问题描述

Java if语句如何在具有赋值和相等性检查时工作或 -d在一起??

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

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

为什么打印错误？

推荐答案

表达式不会按您的想法解析。它不是

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

(test1=false) || (test1 == false)

在这种情况下，结果将是 true ，但是

in which case the result would have been true, but

test1 = (false || test1 == false)

false ||的值test1 == false 表达式首先计算，它是 false ，因为 test1 是设置为 true 进入计算。

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

以这种方式解析它的原因是 || 的http://introcs.cs.princeton.edu/java/11precedence/\">precedence 低于 == 运算符，但高于赋值运算符的优先级 = 。

The reason it is parsed this way is that the precedence of the || is lower than that of the == operator, but higher than the precedence of the assignment operator =.

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