Java程序在一行中进行多种类型转换 [英] Multiple typecasting in a single line in Java program

问题描述

今天，在弄乱Java语法时，我尝试编译以下Java代码：

While messing around with Java syntax today, I tried to compile the following piece of java code:

class Mess {
    public static void main(String[] args) {
        float i = (char)(int)(long)(byte) 100;
        System.out.println(i);
    }
}

该代码实际上没有编译或运行时错误。将 i 的数据类型更改为任何其他数据类型，例如 int 或 double 或 char 也可以。不仅如此，在声明中引入操作也没有任何错误：

The code actually gave no compilation or runtime errors. Changing data type of i to any other data type like int or double or char also worked. Not only this, introducing operations in the declaration also worked without any errors:

float i = (char)+(int)-(long)(byte) 100;

当我在Netbeans中使用自动格式设置代码格式时，上述声明的格式如下：

When I used auto-format in Netbeans to format the code, the above declaration was formatted as follows:

float i = (char) +(int) -(long) (byte) 100;

请帮助我了解如何编译此代码？

Please help me in understanding how this code is compiled?

推荐答案

基本上，它只是一连串的类型转换和一元 + 和-

It's basically just a chain of casts and unary + and -.

float i = (char) +(int) -(long) (byte) 100;

相当于

byte tmp1 = (byte) 100;
long tmp2 = (long) tmp1;
long tmp3 = -tmp2;
int  tmp4 = (int) tmp3;
int  tmp5 = +tmp4;
char tmp6 = tmp5;
float i = tmp6;

最后的任务是从 char 到 float ，这是一个不断扩大的原始转换。请参见 JLS第5章：转化和促销

The final assignment is from char to float, which is a widening primitive conversion. See JLS Chapter 5: Conversions and Promotions

原始类型的19种特定转换称为扩展原始转换：

19 specific conversions on primitive types are called the widening primitive conversions:

• 以字节为单位的short，int，long，float或double


• 以short到int，类型，long，float或double


• 字符转换为整型，整型，浮点型或双精度型


• int转换为整型，浮点型或双精度型


• 可浮动或加倍


• 可浮动可加倍

• byte to short, int, long, float, or double
• short to int, long, float, or double
• char to int, long, float, or double
• int to long, float, or double
• long to float or double
• float to double

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