Java 的类型是什么(long a - double b)

Question

如题中所问:从 long 值中减去 double 值时内部会发生什么？结果是 double 还是 long 类型，这种行为是否甚至在 Java 规范中指定，或者这种行为是特定于 jvm 的？

所以我知道我可以测试自己的 jvm 功能:

    public class Test {

        /**
         * @param args
         */
        public static void main(String[] args) {
        double b = 1000;
        long a = 1000;
        Object c = a - b;
        Class cls = c.getClass();  
        System.out.println("The type of the object is: " + cls.getName());
        }

    }

输出:

    The type of the object is: java.lang.Double

但这在某处指定了吗？或者它是特定于我使用的 jvm？

Answer 1

这是规范的适用部分:

4.2.4。浮点运算

If at least one of the operands to a numerical operator is of type double, then the operation is carried out using 64-bit floating-point arithmetic, and the result of the numerical operator is a value of type double. If the other operand is not a double, it is first widened (§5.1.5) to type double by numeric promotion (§5.6).

http://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.4