问题描述
因此对于布尔值的二元运算符，Java有& ， | ， ^ ，&& 和 || 。
So for binary operators on booleans, Java has &, |, ^, && and ||.
让我们在这里简要总结一下他们的做法：
Let's summarize what they do briefly here:
- JLS 15.22.2 Boolean Logical Operators &, ^, and |
- JLS 15.23 Conditional-And Operator &&
- JLS 15.24 Conditional-Or Operator ||
对于 | ，如果两个操作数值都是 false ，则结果值为 false ;否则，结果是 true 。
For |, the result value is false if both operand values are false; otherwise, the result is true.
对于 ^ ，如果操作数值不同，则结果值为 true ;否则，结果是 false 。
For ^, the result value is true if the operand values are different; otherwise, the result is false.
&& 运算符类似于& 但仅当其左侧操作数的值为 true 。
The && operator is like & but evaluates its right-hand operand only if the value of its left-hand operand is true.
|| 运算符类似于 | ，但仅当其左侧操作数的值为 false 时才计算其右侧操作数。
The || operator is like |, but evaluates its right-hand operand only if the value of its left-hand operand is false.
现在，在所有5个中，有3个具有复合赋值版本，即 | = ，& = 和 ^ = 。所以我的问题很明显：为什么Java不提供&& = 和 || = ？我发现我需要的不仅仅是我需要的& = 和 | = 。
Now, among all 5, 3 of those have compound assignment versions, namely |=, &= and ^=. So my question is obvious: why doesn't Java provide &&= and ||= as well? I find that I need those more than I need &= and |=.
我不认为因为它太长是一个很好的答案，因为Java有>>> = 。这个遗漏必须有更好的理由。
And I don't think that "because it's too long" is a good answer, because Java has >>>=. There must be a better reason for this omission.
来自：
评论如果& ;& = 和 || = 已实施，那么它将是唯一不首先评估右侧的运营商。我相信复合赋值运算符首先评估右侧的概念是错误的。
A comment was made that if &&= and ||= were implemented, then it would be the only operators that do not evaluate the right hand side first. I believe this notion that a compound assignment operator evaluates the right hand side first is a mistake.
来自：
作为证据，以下代码段抛出 NullPointerException ，而不是 ArrayIndexOutOfBoundsException 。
As proof, the following snippet throws a NullPointerException, not an ArrayIndexOutOfBoundsException.
int[] a = null;
int[] b = {};
a[0] += b[-1];
推荐答案
原因
运算符&& = 和 || = 在 Java上不可用因为对于大多数开发人员来说，这些运营商是：
Reason
The operators &&= and ||= are not available on Java because for most of the developers these operators are:
- 容易出错
- 无用的
如果Java允许&& = 运算符，那么该代码：
If Java allowed &&= operator, then that code:
bool isOk = true; //becomes false when at least a function returns false
isOK &&= f1();
isOK &&= f2(); //we may expect f2() is called whatever the f1() returned value
等同于：
bool isOk = true;
if (isOK) isOk = f1();
if (isOK) isOk = f2(); //f2() is called only when f1() returns true
第一个代码是容易出错，因为许多开发人员会认为无论f1（）返回的值是什么，总是会调用 f2（）。它就像 bool isOk = f1（）&& f2（）; 其中 f2（）仅在 f1（）返回时被调用真。
This first code is error-prone because many developers would think f2() is always called whatever the f1() returned value. It is like bool isOk = f1() && f2(); where f2() is called only when f1() returns true.
如果开发人员只想在 f1（） f2（） / code>返回 true ，因此上面的第二个代码不易出错。
If the developer wants f2() to be called only when f1() returns true, therefore the second code above is less error-prone.
Else & = 就足够了，因为开发人员希望始终调用 f2（）：
Else &= is sufficient because the developer wants f2() to be always called:
bool isOk = true;
isOK &= f1();
isOK &= f2(); //f2() always called whatever the f1() returned value
此外，JVM应该运行这个以上代码如下：
Moreover, the JVM should run this above code as the following one:
bool isOk = true;
if (!f1()) isOk = false;
if (!f2()) isOk = false; //f2() always called
比较&& 和& 结果
运营商的结果是&& ; 和& 在布尔值上应用时相同吗？
Compare && and & results
Are the results of operators && and & the same when applied on boolean values?
让我们检查一下以下Java代码：
Let's check using the following Java code:
public class qalcdo {
public static void main (String[] args) {
test (true, true);
test (true, false);
test (false, false);
test (false, true);
}
private static void test (boolean a, boolean b) {
System.out.println (counter++ + ") a=" + a + " and b=" + b);
System.out.println ("a && b = " + (a && b));
System.out.println ("a & b = " + (a & b));
System.out.println ("======================");
}
private static int counter = 1;
}
输出：
1) a=true and b=true
a && b = true
a & b = true
======================
2) a=true and b=false
a && b = false
a & b = false
======================
3) a=false and b=false
a && b = false
a & b = false
======================
4) a=false and b=true
a && b = false
a & b = false
======================
因此是我们可以通过& && $ c>表示布尔值;-)
Therefore YES we can replace && by & for boolean values ;-)
因此最好使用& = 而不是&& = 。
&& = 的原因相同：
运算符 | = 比 || = 更不容易出错。
Same reasons as for &&=:
operator |= is less error-prone than ||=.
如果开发人员想要 f2（）当 f1（）返回 true ，然后我建议以下备选方案：
If a developer wants f2() not to be called when f1() returns true, then I advice the following alternatives:
// here a comment is required to explain that
// f2() is not called when f1() returns false, and so on...
bool isOk = f1() || f2() || f3() || f4();
或：
// here the following comments are not required
// (the code is enough understandable)
bool isOk = false;
if (!isOK) isOk = f1();
if (!isOK) isOk = f2(); //f2() is not called when f1() returns false
if (!isOK) isOk = f3(); //f3() is not called when f1() or f2() return false
if (!isOK) isOk = f4(); //f4() is not called when ...
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