post increment operator java [英] post increment operator java
问题描述
我无法通过joshua bloch从java puzzlers中获取以下代码的正面或反面。
I can't make heads or tails of the following code from "java puzzlers" by joshua bloch.
public class Test22{
public static void main(String args[]){
int j=0;
for(int i=0;i<100;i++){
j=j++;
}
System.out.println(j); //prints 0
int a=0,b=0;
a=b++;
System.out.println(a);
System.out.println(b); //prints 1
}
}
我无法得到j打印的部分0.
据作者说，
I can't get the part where j prints 0. According to the author,
j=j++
类似于
temp=j;
j=j+1;
j=temp;
但是
a=b++
使b 1.
因此它应该被评估像这样，
makes b 1. So it should've evaluated like this,
a=b
b=b+1
按照相同的逻辑，不应该
By following the same logic, shouldn't
j=j++
评估为，
j=j
j=j+1
这里的温度在哪里？
任何解释都将不胜感激。 <<我正在打破这个问题。 ;）>>
先谢谢。
Where does the temp come into picture here? Any explanations would be much appreciated. << I'm breaking my head over this. ;)>> Thanks in advance.
推荐答案
让我们分解你自己的论点：
Let's break down your own argument:
根据作者的说法，
According to the author,
j=j++;
类似于
temp=j;
j=j+1; // increment
j=temp; // then assign
是的，到目前为止你是对的。 ..，但是这里你错了：
Yes, you're right so far..., but here's where you got it wrong:
但是
But
a=b++;
使 b = 1 。所以它应该像这样评估，
makes b=1. So it should've evaluated like this,
a=b; // assign
b=b+1; // then increment
错误！你没有一贯地应用这条规则！您已从增量更改订单然后将分配给分配然后增加 !!!它的实际评估如下：
WRONG! You're not applying the rule consistently! You've changed the order from increment then assign to assign then increment!!! It's actually evaluated like this:
temp=b;
b=b+1; // increment
a=temp; // then assign
此表格的基本分配：
lhs = rhs++;
类似于这样的事情：
temp = rhs;
rhs = rhs+1; // increment
lhs = temp; // then assign
将此应用于 a = b ++; 。然后将它也应用于 j = j ++; 。这就是为什么你得到你得到的结果。
Apply this to a = b++;. Then apply it also to j = j++;. That's why you get the results that you get.
你做的是你提出了你自己的解释 a = b ++; 确实 - 不符合上述规则的错误解释。这是你混乱的根源。
What you did was you came up with your own interpretation of what a = b++; does -- a WRONG interpretation that doesn't follow the above rule. That's the source of your confusion.
- JLS 15.14.2 Postfix Increment Operator
...将值1添加到变量的值中，并将总和存储回变量[ ...]后缀增量表达式的值是存储新值之前的变量的值。
"...the value 1 is added to the value of the variable and the sum is stored back into the variable [...] The value of the postfix increment expression is the value of the variable before the new value is stored."
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