Question

出于某种原因，我无法使下面的代码像它应该的那样工作。这就是我在java中所拥有的：

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，我如何得到从一行到另一行的答案？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！您正在使用内联变量，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'='。这将改变变量的实际值。

所以，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提供了一些很好的小功能，可以缩短它，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成速记。 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));

度过美好的一天！

Answer 2

您遇到的问题是您实际上并没有更改num的值。 Num总是8，所以你只是在数字8上打印各种操作。为什么不尝试这样的事情：

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

进入命令行，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

你现在这样做的方式并不是改变变量的值。

你可以阅读num-4作为＆＃34;如果我从num＆＃34中减去4，那么该数字是多少。

你正在寻找类似num = num - 4的东西，这是＆＃34;分配给num新值，等于从num＆＃34中减去4;

Answer 5

您需要指定新值。

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可以打印出控制台所需的所有变量。

Answer 6

除了最后两行之外，在应用数学运算时，您只需给出println变量的值。最后两行有效，因为++ x / - x代表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”。这意味着你不能直接改变它们（AKA改变它们），你只能创建新的。

如果您想有效修改int num，则必须重新分配。{p>这将使用新值覆盖当前值。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;

但也许更好的可视化方法就是这样想：

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，您不是更改 num，而只是重新分配它。第二个例子是使其更加明确。

打印数字的值会产生意外结果

7 个答案: