Java：将long转换为int

Question

假设变量start和stop都是长型变量。

int diff = (int) start-stop;

这段代码产生错误Type mismatch: cannot convert from long to int ，而

int diff = (int) (start-stop);

运行正常。 为什么？

Answer 1

因为首先， (int)适用于start ，而不适用于表达式，如下所示：

int diff = ((int) start) - stop; // <== Your first expression clarified

然后，从结果int减去long ，该表达式的结果为long 。 （如果它的工作，它可能将不得不给予你一个不正确的结果，如果副作用start曾经有过大在存储值int ）。

通过首先进行减法并获得long结果， 然后将其强制转换为int ，可以将其存储在int变量中。 （大概可以从您的应用程序逻辑中了解它的适用性。）

Answer 2

因为Java不允许隐式缩小转换。 在第一种情况下将需要一个，因为它等效于：

int diff = ((long)(int)start) - stop;

Answer 3

int diff = (int) start - stop;

等于

int diff = (int) (long) start - (long) stop; // we substract long types

可以简化为

int diff = (int) start - (long) stop; // (int)(long) x means (int) x

等于

int diff = ((int) start) - (long) stop; // casting is applied only to start

等于

int diff = ((long)(int) start) - (long) stop; // compiler make types equal

可以简化为

int diff = (long) start - (long) stop; // we can substract now

等于

int diff = (long) startMinusStop; // because long - long => long

这是我们可读的错误Type mismatch: cannot convert from long to int 。

Answer 4

在第一个语句中，您只会将变量start转换为整数。 所以结果是int - long ，这是一个long，不适合整数。

它就像int = (int - long)而Java则不允许。