Java:自增/自减运算符的前缀/后缀? [英] Java: Prefix/postfix of increment/decrement operators?

问题描述

从下面的程序或这里，为什么最后一次调用System.out.println(i) 打印值 7?

From the program below or here, why does the last call to System.out.println(i) print the value 7?

class PrePostDemo {
     public static void main(String[] args){
          int i = 3;
          i++;
          System.out.println(i);    // "4"
          ++i;             
          System.out.println(i);    // "5"
          System.out.println(++i);  // "6"
          System.out.println(i++);  // "6"
          System.out.println(i);    // "7"
     }
}

推荐答案

i = 5;
System.out.println(++i); //6

这会打印出6"因为它需要 i，加一，然后返回值:5+1=6.这是前缀，在操作中使用之前添加到数字中.

This prints out "6" because it takes i, adds one to it, and returns the value: 5+1=6. This is prefixing, adding to the number before using it in the operation.

i = 6;
System.out.println(i++); //6 (i = 7, prints 6)

这会打印出6"因为它需要 i，存储一个副本，给变量加 1，然后返回副本.所以你得到了 i 的值，但同时也增加了它.因此，您打印出旧值，但它会增加.后缀增量的美妙之处.

This prints out "6" because it takes i, stores a copy, adds 1 to the variable, and then returns the copy. So you get the value that i was, but also increment it at the same time. Therefore you print out the old value but it gets incremented. The beauty of a postfix increment.

然后当你打印出 i 时，它显示了 i 的真实值，因为它已经增加了:7.

Then when you print out i, it shows the real value of i because it had been incremented: 7.

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