The static modifier that precedes $onlyOne ties the variable to the class itself.
$onlyOne 之前的静态修饰符将此变量关系到类本身。
2
The $onlyOne variable is said to be a class attribute, as it is scoped to the class.
$onlyOne 变量是一个类属性,因为其作用域是这个类。
3
RealMeter represents the highest industrial-level, especially for some famous helium leak detector brand. RealMeter is the onlyone whose maintenance can be done at the circuit level in China.