int到short具有两个最显著字节

Question

我有一个整数

int a = //... 

int S IN的java包括4个字节。如果我们将其转换为short，我们将采用两个最低有效字节。 short由int的2个最重要的byte组成的最快方式是什么？

short b = //take two most significant bytes of a 

Answer 1

short b = (short) (a >> 16); 

Answer 2

就足够了使用右位移位运算符（>>）。由于int基本数据类型具有32位（Primitive Data Types (The Java™ Tutorials > Learning the Java Language > Language Basics)）的大小和你需要得到16个最显著位，有必要通过16位执行右位移位：

public class Program { 
    public static void main(final String[] args) { 
     final int input = 0xABCDEFAB; 
     final short output = (short) (input >> 16); 
     System.out.printf("Original integer: %X%n", input); 
     System.out.printf("Short with two most significant bytes: %X%n", output); 
    } 
} 

而且，值得注意的是Java语言已经签名（<<,>>）和无符号（<<<,>>>）移位运算符。请参阅文章：Bitwise and Bit Shift Operators (The Java™ Tutorials > Learning the Java Language > Language Basics)。

同样的结果可以用除法运算产生：

public class Program { 
    public static void main(final String[] args) { 
     final int input = 0xABCDEFAB; 
     final short output = (short) (input/0x10000); 
     System.out.printf("Original integer: %X%n", input); 
     System.out.printf("Short with two most significant bytes: %X%n", output); 
    } 
}