android 類型轉換 工具函數

android中類型轉換好像支援不是太好，備份下有用的類型轉換函式和工具函數.

一、類型轉換

1.byte 轉 int   ( int 可以再轉成long double float ）

[java] 
public static int byteToInt(byte[] data, int offset) 
{ 
        int result = 0; 
    int n1, n2, n3, n4; 
     
    n1 = data[offset + 3] & 0xFF; 
    n2 = data[offset + 2] & 0xFF; 
    n3 = data[offset + 1] & 0xFF; 
    n4 = data[offset] & 0xFF; 
         
    result = n1 << 24  | n2 << 16 | n3 << 8 | n4; 
         
    return result; 
} 

2. byte 轉 Hex
[java] www.2cto.com
public static String toHexString(byte[] b)  
{ 
    char HEX_DIGITS[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 
                  'A', 'B', 'C', 'D', 'E', 'F' }; 
         
        StringBuilder sb = new StringBuilder(b.length * 2); 
        for (int i = 0; i < b.length; i++) 
        { 
            sb.append(HEX_DIGITS[(b[i] & 0xf0) >> 4]); 
            sb.append(HEX_DIGITS[b[i] & 0x0f]); 
        } 
        return sb.toString(); 
} 

3. HexString 轉 long

[java] 
public static long hexStringToLong(String s) 
{ 
    String serial = "0123456789ABCDEF"; 
                 
    s = s.trim().toUpperCase(); 
    if( s.length() > 8 ) return 0; 
         
    long num = 0; 
    int  len = s.length(); 
         
    for( int i = 0; i < len; i++) 
    { 
        num += (serial.indexOf( s.charAt(i) ) << (4 * (len - i - 1))); 
    } 
         
    return num; 
} 

二、 工具函數
1. md5sum

[java] 
public static String getMd5sum(String filename)  
{ 
        InputStream fis; 
        byte[] buffer = new byte[1024]; 
        int numRead = 0; 
        MessageDigest md5; 
        try{ 
            fis = new FileInputStream(filename); 
            md5 = MessageDigest.getInstance("MD5"); 
            while((numRead=fis.read(buffer)) > 0) { 
                md5.update(buffer,0,numRead); 
            } 
            fis.close(); 
            return toHexString(md5.digest());   
        } catch (Exception e) { 
            return null; 
        } 
}