Java：增量/减量运算符的前缀/后缀？ [英] Java: Prefix/postfix of increment/decrement operators?

问题描述

从下面的程序或这里，为什么最后一次打电话给 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

这打印出6，因为它需要我添加一个并返回值。 5 + 1 = 6;这是前缀，在操作中使用前添加数字。

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)

这打印出6，因为它需要我，存储副本，添加1并返回副本。所以你得到了我的价值，但也同时增加了它。因此，您打印旧值但它会增加。后缀增量的美妙。

This prints out "6" because it takes i, stores a copy, adds 1 and 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 beautfy of a postfix increment.

然后当你打印出i时，它显示了i的实际值，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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