[英]Java clarification on += assignment operator
我对+ =赋值运算符的工作方式有些困惑。 我知道x + = 1是x = x + 1。 但是,此代码中有一个字符串变量,称为“字符串输出”,并使用空字符串初始化。 我的困惑是变量“输出”有5个不同的输出,但我看不到它的存储位置。 帮助澄清我的误会。 我似乎无法弄清楚。
import java.util.Scanner;
public class SubtractionQuiz {
public static void main(String[] args) {
final int NUMBER_OF_QUESTIONS = 5; //number of questions
int correctCount = 0; // Count the number of correct answer
int count = 0; // Count the number of questions
long startTime = System.currentTimeMillis();
String output = " "; // Output string is initially empty
Scanner input = new Scanner(System.in);
while (count < NUMBER_OF_QUESTIONS) {
// 1. Generate two random single-digit integers
int number1 = (int)(Math.random() * 10);
int number2 = (int)(Math.random() * 10);
// 2. if number1 < number2, swap number1 with number2
if (number1 < number2) {
int temp = number1;
number1 = number2;
number2 = temp;
}
// 3. Prompt the student to answer "What is number1 - number2?"
System.out.print(
"What is " + number1 + " - " + number2 + "? ");
int answer = input.nextInt();
// 4. Grade the answer and display the result
if (number1 - number2 == answer) {
System.out.println("You are correct!");
correctCount++; // Increase the correct answer count
}
else
System.out.println("Your answer is wrong.\n" + number1
+ " - " + number2 + " should be " + (number1 - number2));
// Increase the question count
count++;
output += "\n" + number1 + "-" + number2 + "=" + answer +
((number1 - number2 == answer) ? " correct" : "
wrong");
}
long endTime = System.currentTimeMillis();
long testTime = endTime = startTime;
System.out.println("Correct count is " + correctCount +
"\nTest time is " + testTime / 1000 + " seconds\n" + output);
}
}
其Add AND赋值运算符 。
它将右操作数添加到左操作数,并将结果分配给左操作数。
就你而言
output += someString // output becomes output content +somestring content.
`
也许写了正确的答案,但是如果我正确理解了您的问题,那么您需要澄清一下,而不是+ =的意思。
更改代码;
// Increase the question count
count++;
output += "\n" + number1 + "-" + number2 + "=" + answer +
((number1 - number2 == answer) ? " correct" : "wrong");
这样:
output += "\nCount: " + count + " and the others: " +
number1 + "-" + number2 + "=" + answer +
((number1 - number2 == answer) ? " correct" : "wrong");
// Increase the question count
count++;
这样您就可以同时看到行和计数。 然后按照您的意愿增加。
在Java中,字符串是不可变的。 所以output += somethingNew
会产生这样的结果:
String temp = output;
output = temp + somethingNew;
最后,它变得像concat / merge
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