数字文字中的 Java 7 下划线 [英] Java 7 underscore in numeric literals
问题描述
当我们必须使用 _ 来分隔数字中的数字时，我不明白以下无法使用它的情况:
When we must use a _ to separate digits in a number I don't understand the following case in which I can't use it:
在需要一串数字的位置
(如 JDK7 指南中所述此处)
(as documented in the JDK7 guide here)
一些例子?
推荐答案
您不必必须使用_"，您可以.提案中给出的示例是信用卡号、电话号码，或者只是在代码中使用分隔符才有意义的数字.
You don't have to use "_", you can. And examples given in the proposal are credit card numbers, phone numbers, or simply numbers for which it makes sense to have a separator in the code.
对于在需要一串数字的位置"，它只是在应该以数字开头(或结尾)的地方.以下是一些示例.
For the "In positions where a string of digits is expected" it's simply in places where it's supposed to start (or end) with a digit. Here are some examples.
注意，根据这个提议，下划线只能放在数字之间.它们不能单独放置在通常需要一串数字的位置:
Note that according to this proposal, underscores can only be placed between digits. They cannot be placed by themselves in positions where a string of digits would normally be expected:
int x1 = _52;//这是一个标识符，不是数字文字.
int x1 = _52; // This is an identifier, not a numeric literal.
int x2 = 5_2;//好的.(十进制文字)
int x2 = 5_2; // OK. (Decimal literal)
int x2 = 52_;//非法的.(下划线必须始终在数字之间)
int x2 = 52_; // Illegal. (Underscores must always be between digits)
int x3 = 5_______2;//好的.(十进制文字.)
int x3 = 5_______2; // OK. (Decimal literal.)
int x4 = 0_x52;//非法的.不能在0x"基数前缀中添加下划线.
int x4 = 0_x52; // Illegal. Can't put underscores in the "0x" radix prefix.
int x5 = 0x_52;//非法的.(下划线必须始终在数字之间)
int x5 = 0x_52; // Illegal. (Underscores must always be between digits)
int x6 = 0x5_2;//好的.(十六进制文字)
int x6 = 0x5_2; // OK. (Hexadecimal literal)
int x6 = 0x52_；//非法的.(下划线必须始终在数字之间)
int x6 = 0x52_; // Illegal. (Underscores must always be between digits)
int x6 = 0x_；//非法的.(删除下划线后无效)
int x6 = 0x_; // Illegal. (Not valid with the underscore removed)
int x7 = 0_52;//好的.(八进制文字)
int x7 = 0_52; // OK. (Octal literal)
int x7 = 05_2;//好的.(八进制文字)
int x7 = 05_2; // OK. (Octal literal)
int x8 = 052_;//非法的.(下划线必须始终在数字之间)
int x8 = 052_; // Illegal. (Underscores must always be between digits)
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