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This article introduces the relevant knowledge of "how to solve the data overflow problem encountered in the process of Java timestamp calculation". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Background

Today, in the process of running a timing task, it is found that there is an exception in setting the query time range of the data, and there is a strange phenomenon that the start timestamp is larger than the end timestamp. The code for calculating the timestamp is roughly as follows.

Package com.lingyejun.authenticator; public class IntegerTest {public static void main (String [] args) {long endTime = System.currentTimeMillis (); long startTime = endTime-30 * 24 * 60 * 60 * 1000; System.out.println ("end:" + endTime); System.out.println ("start:" + startTime);}}

Let's first draw a conclusion: because the integer in java is int by default, the result of 30 * 24 * 60 * 60 * 1000 is greater than that of Integer.MAX_VALUE in the process of calculation, so there is a data overflow, resulting in inaccurate results.

Verification

Let's modify the above code a little bit to make it easier for us to identify the location problem. The adjusted code is as follows:

Package com.lingyejun.authenticator; public class IntegerTest {public static long calcStartTime (long endTime, long minusMills) {System.out.println ("end:" + endTime + "minus mills:" + minusMills); long startTime = endTime-minusMills; System.out.println ("start:" + startTime); return startTime;} public static void main (String [] args) {long nowTime = System.currentTimeMillis (); long a = 30 * 24 * 60 * 1000; calcStartTime (nowTime, a);}}

The results are as follows:

End: 1560869539864 minus mills:-1702967296start: 1562572507160

This is not what we expected, because 30 * 86400000 = 2592000000, but the calculation is:-1702967296.

By now, everyone must know why, because the default type of integers in java is integer int, and the maximum value of int is 2147483647.

In the code, java calculates the right value first, and then assigns it to the long variable. An overflow occurs during the calculation of the right value (int multiplication), and then the truncated value after the overflow is assigned to the variable, resulting in inaccurate results.

Make a small change to the code and take another look.

Package com.lingyejun.authenticator; public class IntegerTest {public static long calcStartTime (long endTime, long minusMills) {System.out.println ("end:" + endTime + "minus mills:" + minusMills); long startTime = endTime-minusMills; System.out.println ("start:" + startTime); return startTime;} public static void main (String [] args) {long nowTime = System.currentTimeMillis (); long a = 30 * 24 * 60 * 1000L; calcStartTime (nowTime, a);}}

The result is

End: 1560869539864 minus mills: 2592000000start: 1558277539864

It seems that there should be no problem, but is it really safe? if I want to adjust 30 to 24856 (Integer.MAX_VALUE / 86400 = 24855), that is, long a = 24856 * 24 * 60 * 1000L, then the overflow will also occur.

Because the operation rule of java overflowed before multiplying the last long 1000 from left to right, the result is also wrong, and the correct way should be as follows: long a = 24856L * 24 * 60 * 60 * 1000.

Package com.lingyejun.authenticator; public class IntegerTest {public static long calcStartTime (long endTime, long minusMills) {System.out.println ("end:" + endTime + "minus mills:" + minusMills); long startTime = endTime-minusMills; System.out.println ("start:" + startTime); return startTime;} public static void main (String [] args) {long a = 30L * 24 * 60 * 60 * 1000; calcStartTime (nowTime, a);}}

This is the end of the content of "how to solve the data overflow problem encountered in the process of Java timestamp calculation". Thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

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