int到short具有兩個最顯著字節

Question

我有一個整數

int a = //... 

int S IN的java包括4個字節。如果我們將其轉換爲short，我們將採用兩個最低有效字節。 short由int的2個最重要的byte組成的最快方式是什麼？

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

Answer 1

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

Answer 2

就足夠了使用右位移位運算符（>>）。由於int基本數據類型具有32位（Primitive Data Types (The Java™ Tutorials > Learning the Java Language > Language Basics)）的大小和你需要得到16個最顯著位，有必要通過16位執行右位移位：

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語言已經簽名（<<,>>）和無符號（<<<,>>>）移位運算符。請參閱文章：Bitwise and Bit Shift Operators (The Java™ Tutorials > Learning the Java Language > Language Basics)。

同樣的結果可以用除法運算產生：

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); 
    } 
}