打印数字值会产生意外结果

Question

由于某种原因，我无法使以下代码正常工作。 这就是我在java中的功能：

int num = 8; 

System.out.println("Value is now " + (num));
System.out.println("Value is now " + (num+2));
System.out.println("Value is now " + (num-4));
System.out.println("Value is now " + (num*5));
System.out.println("Value is now " + (num/3));
System.out.println("Value is now " + (++num));
System.out.println("Value is now " + (--num));

它打印以下内容：

Value is now 8
Value is now 10
Value is now 4
Value is now 40
Value is now 2
Value is now 9
Value is now 8

我期待得到这个：

Value is now 8
Value is now 10
Value is now 6
Value is now 30
Value is now 10
Value is now 11
Value is now 10

那么，我如何获得答案来沿线进行呢？ 我一直在阅读和搜索，找不到正确的方法。

Answer 1

一个常见的错误！ 您正在内联使用变量，这意味着变量本身不会被更改。 为了实际更改变量，您需要使用“ =”。 这将更改变量的实际值。

因此，例如

int num = 8;

System.out.println("Value is now " + (num));
num = num + 2;
System.out.println("Value is now " + (num));
num = num - 4;
System.out.println("Value is now " + (num));
num = num * 5;
System.out.println("Value is now " + (num));
num = num / 3;
System.out.println("Value is now " + (num));
System.out.println("Value is now " + (++num));
System.out.println("Value is now " + (--num));

现在，这是很多代码。 Java提供了一些可以缩短此时间的不错的小功能，称为“语法糖”。 首先，“ =”将返回设置为变量的值。 所以现在我们可以这样写：

int num = 8;

System.out.println("Value is now " + (num));
System.out.println("Value is now " + (num = num + 2));
System.out.println("Value is now " + (num = num - 4));
System.out.println("Value is now " + (num = num * 5));
System.out.println("Value is now " + (num = num / 3));
System.out.println("Value is now " + (++num));
System.out.println("Value is now " + (--num));

接下来，我们可以将这些操作写为简写。 num = num + 2变为num+=2 ， num = num * 5变为num*=5 ，依此类推。

因此，我们可以将整个代码编写为：

int num = 8;

System.out.println("Value is now " + (num));
System.out.println("Value is now " + (num += 2));
System.out.println("Value is now " + (num -= 4));
System.out.println("Value is now " + (num *= 5));
System.out.println("Value is now " + (num /= 3));
System.out.println("Value is now " + (++num));
System.out.println("Value is now " + (--num));

祝你今天愉快！

Answer 2

您遇到的问题是您实际上没有更改num的值。 Num始终为8，因此您只是在数字8上打印各种运算。为什么不尝试这样的操作：

int num = 8; 
System.out.println("Value is now " + (num));
num += 2;
System.out.println("Value is now " + (num));
num -= 4;
System.out.println("Value is now " + (num));
num *= 5;
System.out.println("Value is now " + (num));
num /= 3;
System.out.println("Value is now " + (num));
num++;
System.out.println("Value is now " + (num));
num--;
System.out.println("Value is now " + (num));

编辑

在命令行中运行，收到预期的输出：

Value is now 8
Value is now 10
Value is now 6
Value is now 30
Value is now 10
Value is now 11
Value is now 10

Answer 3

只需将新值分配给变量即可。

int num =8 
System.out.println("Value is now " + num);
num = num +2;
System.out.println("Value is now " + num);
num = num -4;
System.out.println("Value is now " + num);
num = num *5;
System.out.println("Value is now " + num);
......

Answer 4

您现在的操作方式是不更改变量的值。

您可以将num-4读为“如果我从num减去4将会是多少”。

您正在寻找类似num = num - 4东西，这是“分配给num等于从num减去4的新值”。

Answer 5

您需要分配新值。

System.out.println("Value is now " + (num));
System.out.println("Value is now " + (num+=2));
System.out.println("Value is now " + (num-=4));
System.out.println("Value is now " + (num*=5));
System.out.println("Value is now " + (num/=3));
System.out.println("Value is now " + (++num));
System.out.println("Value is now " + (--num));

System.out.println可以将所需的所有变量打印到控制台。

Answer 6

除了最后两行之外，您只是在对数学应用变量时就给println赋值。 最后两行有效，因为++ x /-x表示x = x + 1或减号。 您需要以这种方式分配变量，以使代码按指定的方式工作。

Answer 7

在Java中，原语（例如： int ）是“不可变的”。 这意味着您不能直接更改它们（也就是更改它们），只能创建新的。

如果要有效地修改int num ，则必须重新分配它。 这将用新值覆盖当前值。 这是一个例子：

int num = 8;
System.out.println("Value is now " + num);
num = num + 2;
System.out.println("Value is now " + num);
num = num + 2;

但是，将其可视化的更好方法是这样考虑：

int num1 = 8;
System.out.println("Value is now " + num1);
int num2 = num1 + 2;
System.out.println("Value is now " + num2);
int num3 = num2 + 2;

我说这是一种更好的可视化方法，因为在原始示例中，您没有更改 num ，而只是重新分配了它。 第二个示例使这一点更加明确。