Java整型到短型转换规则

Question

在代码中，只有第一种情况（整数变量到short）有编译错误（从int到short的有损转换）。为什么其他情况（整数字面改为short，最终整数变量改为short）没有这个相同的编译错误呢？

public class Test
{   
    public static void main(String[] args)
    {
        short shortNum = 0;
        
        //integer variable to short
        int intNum = 12;
        shortNum = intNum;
        
        //integer literal to short
        shortNum = 12;

        //final integer variable to short
        final int finalNum = 12;
        shortNum = finalNum;
    }
}

Answer 1

将答案视为注释：

short shortNum = 0;

//integer variable to short
int intNum = 12;
shortNum = intNum; //doesn't work, because casting primitives is required any time you are going from a larger numerical data type to a smaller numerical data type.
        
//integer literal to short
shortNum = 12; //This is not integer literal per se, you're initializing your short variable with 12, which fits in short data type, so it's short.

//final integer variable to short
final int finalNum = 12; //your variable is final, and according to Java Language Specification, if final variable's value fits into the type you're casting it, then no explicit cast is needed.
shortNum = finalNum;