JAVA：不是声明 - 用于调用 'long'？

Question

下面这段代码是我写的

public long secFromMidnight()
{
     long seconds_from_midnight = (this._hour * SEC_IN_HOUR) + (this._minute * SEC_IN_MIN) + (this._second);
     return seconds_from_midnight;
}

public int difference(Time1 other)
{
    long 1stSEC = null;
    long 2ndSEC = null;
    1stSEC= this.secFromMidnight();
    2ndSEC = other.secFromMidnight();
    return (int)(1stSEC - 2ndSEC);
}

当我尝试编译时，"long 1stSEC = null";

出现 "Not a Statement" 错误

为什么会这样？我之前可以在方法中声明一个long变量..

Answer 1

变量的名称不能以数字开头。

Variable names are case-sensitive. A variable's name can be any legal identifier — an unlimited-length sequence of Unicode letters and digits, beginning with a letter, the dollar sign "$", or the underscore character "". The convention, however, is to always begin your variable names with a letter, not "$" or "".

Java variables' naming conventions

此外，long 是一个 原始类型 ，因此您不能将 null 分配给 long 变量。将其设置为 0。

Answer 2

用正确的名称重命名这些变量，而不是用 null 初始化它们，而是用 0 初始化它们，例如：

 long sEC1st = 0;
 long sEC2nd = 0;

Using ALL uppercase letters are primarily used to identify constant variables. Remember that variable names are case-sensitive. You cannot use a java keyword (reserved word) for a variable name.

JAVA：不是声明 - 用于调用 'long'？

JAVA: Not a statement - for calling 'long'?

java

methods

long-integer