数组的预增量

Question

谁能解释这段代码的输出？我一直很难理解，但我就是不明白。

public static void main(String ars[]) {
    int responses[] = {1,2,4,4};
    int freq[] = new int[5];

    for(int answer = 1; answer < responses.length; answer++) {
        ++freq[responses[answer]];
    }

    for (int rating = 1; rating < freq.length; rating++)
         System.out.printf("%6d%10d\n", rating, freq[rating]);
}

输出

 1         0
 2         1
 3         0
 4         2

Answer 1

在第一个循环中 ++freq[responses[answer]];意思是：

• responses[answer] 从响应数组索引中获取值。
• Freq[value] 检查并从过滤器数组索引中获取值。
• ++Freq[value] 将值 1 添加到 Freq[value]。

Answer 2

我试着把事情简单化了一点，这样你就可以看到发生了什么：

    int responses[] = new int[4];
    responses[0] = 1;
    responses[1] = 2;
    responses[2] = 4;
    responses[3] = 4;

    int freq[] = new int[5];

    for(int answer = 1; answer < 4; answer++)
    {
        int x = responses[answer];
        freq[x] = freq[x] + 1;
    }

    for (int rating = 1; rating < 5; rating++)
    {  
         //Print 6 spaces and then the rating variable
         //Print 10 spaces then the integer at freq[rating]

         System.out.printf("%6d%10d\n", rating, freq[rating]);
    } 

我会查找++ prefix & postfix。