Java允许你在数字字面量中使用下划线。此功能是Java 7中引入的。例如, 该功能使你可以分隔数字字面量中的数字组, 这可以提高源代码的可读性。

以下几点很重要：

你不能在数字的开头或结尾使用下划线。

Ex. int a = _10; // Error, this is an identifier, not a numeric literal

Ex. int a = 10_; // Error, cannot put underscores at the end of a number

你不能在浮点文字中的小数点附近使用下划线。

Ex. float a = 10._0; // Error, cannot put underscores adjacent to a decimal point

Ex. float a = 10_.0; // Error, cannot put underscores adjacent to a decimal point

你不能在F或L后缀之前使用下划线

Ex. long a = 10_100_00_L; // Error, cannot put underscores prior to an L suffix

Ex. float a = 10_100_00_F; // Error, cannot put underscores prior to an F suffix

你不能在需要一串数字的位置使用下划线。

数字字面量示例中的下划线

public class UnderscoreInNumericLiteralExample {

public static void main(String[] args) {

// Underscore in integral literal

int a = 10_00000;

System.out.println("a = "+a);

// Underscore in floating literal

float b = 10.5_000f;

System.out.println("b = "+b);

// Underscore in binary literal

int c = 0B10_10;

System.out.println("c = "+c);

// Underscore in hexadecimal literal

int d = 0x1_1;

System.out.println("d = "+d);

// Underscore in octal literal

int e = 01_1;

System.out.println("e = "+e);

}

}

输出：

a = 1000000

b = 10.5

c = 10

d = 17

e = 9