计数器如何工作？ / 非常基础的 Java
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How the counter works? / Very basic Java
提问by StraDis
I have a code from a book with a counter in it. I don't understand why it works the way it does. To be specific, how does it happen that counter counts the lines generated by "for" loop? I see that there is an "if" loop with relational operator and conditional expression but it's still isn't clear to me how the code "knows" to count the lines. Here is a code :
我有一本书的代码，里面有一个计数器。我不明白为什么它的工作方式如此。具体来说，计数器如何计算“for”循环生成的行数？我看到有一个带有关系运算符和条件表达式的“if”循环，但我仍然不清楚代码如何“知道”计算行数。这是一个代码：
*/
class GalToLitTable {
public static void main(String args[]) {
double gallons, liters;
int counter;
counter = 0;
for(gallons = 1; gallons <= 100; gallons++) {
liters = gallons * 3.7854; // convert to liters
System.out.println(gallons + " gallons is " +
liters + " liters.");
counter++;
// every 10th line, print a blank line
if(counter == 10) {
System.out.println();
counter = 0; // reset the line counter
}
}
}
Any help would be much appreciated
任何帮助将非常感激
回答by Rion Williams
There are three things going on here:
这里发生了三件事：
- You have a
forloop that is going to execute 100 times (from 1-100) - Within the loop, you'll increment your counter via the increment operator
++, which is essentially the same as callingcounter = counter + 1;. - Within your loop (after the increment), you'll check the current value to see if you should perform some action (in this case, resetting the counter).
- 您有一个
for要执行 100 次的循环（从 1-100） - 在循环中，您将通过 increment operator 增加您的计数器
++，这与调用counter = counter + 1;. - 在您的循环中（在增量之后），您将检查当前值以查看是否应该执行某些操作（在这种情况下，重置计数器）。
You can see some annotated code below, which explains this a bit better, but I'd highly encourage you to see the links provided above for a bit more detail on the forloop and incrementoperator:
您可以在下面看到一些带注释的代码，这更好地解释了这一点，但我强烈建议您查看上面提供的链接，以了解有关for循环和increment运算符的更多详细信息：
// Your counter
int counter = 0;
// The contents of this will execute 100 times
for(gallons = 1; gallons <= 100; gallons++) {
// Omitted for brevity
// This increases your counter by 1
counter++;
// Since your counter is declared outside of the loop, it is accessible here
// so check its value
if(counter == 10) {
// If it is 10, then reset it
System.out.println();
counter = 0;
}
// At this point, the loop is over, so go to the next iteration
}
回答by Musti
counter ++;means counter = counter + 1;This line of code increments the counter by one on every iteration of the foor loop. The If-Clause, resets the counter to zero, when it has reached 10, as you see in counter = 0;. So after 10 iterations the counter reaches 10 and the condition of the if clause is true.
counter ++;意味着counter = counter + 1;这行代码在 for 循环的每次迭代中将计数器加一。If-Clause 将计数器重置为零，当它达到 10 时，如您在 中看到的counter = 0;。因此，在 10 次迭代后，计数器达到 10，并且 if 子句的条件为真。
