java - 自动装箱:为什么 Short S1 = 100；编译正常，但 Long F1 = 100；失败的？

Question

我知道编译 Long F1 = 100; 会失败，因为 100 是一个整数，所以编译器会将其装箱为 Integer，并且包装器类型无法扩展.

但是为什么编译 Short S1 = 100; 会成功呢？非常感谢您的帮助。

Answer 1

来自 SCJP: 的第 3 章

The following is legal,

byte b = 27;

but only because the compiler automatically narrows the literal value to a byte. In other words, the compiler puts in the cast. The preceding code is identical to the following:

byte b = (byte) 27; // Explicitly cast the int literal to a byte

It looks as though the compiler gives you a break, and lets you take a shortcut with assignments to integer variables smaller than an int. (Everything we're saying about byte applies equally to char and short, both of which are smaller than an int)

在您的情况下，编译器正在使用:

Short s = (short)100;