Expression puzzles, expressions

Expression puzzles, expressions

I. Judge odd numbers

When it comes to determining odd numbers, the first response is I % 2 = 1; however, this is a big problem;

The statement of negative number is incorrect !! BecauseNegative % 2 =-1

　　So it can be improvedI % 2! = 0;

　　It can also be further optimized. As we all know, bit operations are extremely fast, so there are:I & 1! = 0; => optimal solution !!!

Ii. Change Time

Change:2-1.1 =?

　　Direct output: System. out. println (2-1.1); ==>0.8999999999999999

　　　　This is because not all decimal places in the computer can be exactly expressed in binary,

　　　　BigDecimal can be used for exact representation, and must be usedBigDecimal (String)　

Improvement: printf can be used for output !!

　　　　　　System. out. printf ("%. 2f", 2-1.1 );

Optimization: Using BigDecimal:

System. out. println (new BigDecimal ("2.00"). subtract (new BigDecimal ("1.10 ")));

3. Long division

Long/long

The number of milliseconds in a day/The number of microseconds in a day

final long weimiao = 24 * 60 * 60 * 1000 * 1000;final long haomiao = 24 * 60 * 60 * 1000;        System.out.println(weimiao / haomiao);　　//5

 

This is caused by weimiao overflow. Although the computation results do not overflowIn the calculation process, it is calculated as int type., Weimiao generates overflow, causing an error in the result !!!

The solution is simple. Replace the int constant with a long constant as the factor of every product:

1 final long weimiao = 24L * 60 * 60 * 1000 * 1000;2 final long haomiao = 24L * 60 * 60 * 1000;3         4 System.out.println(weimiao / haomiao);　　//1000

The result is correct !!

　　When operating a large number, always pay attention to the overflow problem. If you are not sure, use long for calculation !!

Iv. hexadecimal

System. out. println (Long. toHexString (0x00000000l + 0 xcafebabe); ==> cafebabe

　　　! If the highest bit of the hexadecimal or octal literal constant is set, it is a negative number !!!!

　Where long + int ==> is automatically converted to long + long

In addition, the second number symbol extension:

　　　　

You can program the second number to the long type to avoid destructive symbol extension !!

　System. out. println (Long. toHexString (0x00000000l + 0 xcafebabeL); ==> 1 cafebabe