[英]unexpected increment result in java array
While learning how to declare, initialize and access the array elements in java, I wrote this simple code: 在学习如何声明,初始化和访问java中的数组元素时,我编写了这个简单的代码:
class ArrayAccess{
public static void main(String args[]){
int[] a;
a = new int[4];
a[0] = 23;
a[1] = a[0]*2;
a[2] = a[0]++;
a[3]++;
int i = 0;
while(i < a.length){
System.out.println(a[i]);
i++;
}
}
}
But I am getting unexpected output. 但我得到了意想不到的输出。
The output I am getting is: 我得到的输出是:
24
46
23
1
So, 所以,
Why 24
instead of 23
as the value of a[0]
? 为什么
24
而不是23
作为a[0]
的值? If this is due increment of a[0]
at a[2]
then why a[1]
's element is 46
and not 48
. 如果这是
a[2]
a[0]
增量,则为什么a[1]
的元素是46
而不是48
。
why 23
instead of 24
as the value of a[2]
? 为什么
23
而不是24
作为a[2]
的值?
a[2] = a[0]++;
incremnets a[0] after copying the value into a[2] 将值复制到[2]后,递增a [0]
Its the same as: 它与以下相同:
a[2] = a[0];
a[0]+=1;
If you want to increment the value before the assignation use a[2] = ++(a[0]);
如果要在赋值前增加值,请使用
a[2] = ++(a[0]);
This ist the same as: 这与以下相同:
a[0]+=1;
a[2] = a[0];
a[2] = a[0]++;
is 是
int temp = a[0];
a[2] = a[0];
a[0] = temp + 1;
Because of the following line: 由于以下行:
a[2] = a[0]++;
Increment (++) has a side effect of incrementing the right-side value. 增量(++)具有增加右侧值的副作用。 Otherwise you should use:
否则你应该使用:
a[2] = a[0]+1;
Another example is the similar concept of ++number. 另一个例子是++编号的类似概念。 If you had written:
如果你写了:
a[2] = ++a[0];
a[0] would be incremented, and THEN added to a[2]. a [0]将递增,然后添加到[2]。 So in a[2] you would have: 24
所以在[2]中你会得到:24
small modification in your prog required 你所需要的小修改
class ArrayAccess{ class ArrayAccess {
public static void main(String args[]){
int referenceNumber= 23;
int[] a;
a = new int[4];
a[0] = referenceNumber;
a[1] = a[0]*2;
a[2] = referenceNumber++;
a[3]++;
int i = 0;
while(i < a.length){
System.out.println(a[i]);
i++;
}
}
} }
now lets come to questions 现在让我们来问问题
Why 24 instead of 23 as the value of a[0]? 为什么24而不是23作为a [0]的值? If this is due increment of a[0] at a[2] then why a[1]'s element is 46 and not 48.
如果这是[2]的[0]的正确增量,则为什么[1]的元素是46而不是48。
yes it is due of increment of a[0] at a[2].
是的,这是由于[2]的a [0]的增量。 But point is the moment u are doing a[1] = a[0]*2;
但关键是你正在做[1] = a [0] * 2的那一刻; its not incremented yet.
它还没有增加。
why 23 instead of 24 as the value of a[2]? 为什么23而不是24作为a [2]的值?
you are doing a[2] = a[0]++;
你正在做[2] = a [0] ++; whats happening is first value of a[0] is assigned to a[2] and then ultimately value at a[0] is incremented not at a[2]
发生的是a [0]的第一个值被分配给[2],然后最终a [0]的值增加而不是[2]
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