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  Greedy and Nongreedy Matching in a Regular Expression

By default, pattern matching is greedy, which means that the matcher returns the longest match possible. For example, applying the pattern A.*c to AbcAbcA matches AbcAbc rather than the shorter Abc. To do nongreedy matching, a question mark must be added to the quantifier. For example, the pattern A.*?c will find the shortest match possible. COPY // Greedy quantifiers String match = find("A.*c", "AbcAbc"); // AbcAbc match = find("A.+", "AbcAbc"); // AbcAbc // Nongreedy quantifier...

   Regular expression,Pattern match,Greedy,     2011-08-09 12:42:28

  Java AbstractMethodError explained and demonstrated

According to Oracle Java API documentation, AbstractMethodError is a kind of runtime error where the application is having some incompatible changes which leads to a missing implementation of an abstract method. Below is the official description. Thrown when an application tries to call an abstract method. Normally, this error is caught by the compiler; this error can only occur at run time if the definition of some class has incompatibly changed since the currently executing method was last co...

   JAVA,ABSTRACTMETHODERROR     2016-07-22 22:03:20

  Remote execute command in Java example

Frequently there is a need to logon to a remote system and run some commands or programs to get the output, many software can serve this purpose such as putty and gitshell.These software usually provide secure access to the remote system. But have you ever wondered what to do if you need to run commands on many different systems at the same time and get all these results back at a single place? Especially in big data era, many tasks may run on different distributed systems and you want o have a ...

   JSch, Example, Distributed system, SSH2     2014-12-12 03:20:19

  The hidden risk of passing slice as function parameter

In Go's source code or other open source libraries, there are lots of cases where a slice pointer is passed to function instead of slice itself. This brings up a doubt why not passing slice directly as its internal is backed by an array pointer to point to underlying data? For example, in log package, the formatHeader function takes a parameter buf as type *[]byte instead of []byte. func (l *Logger) formatHeader(buf *[]byte, t time.Time, file string, line int) {} Let's understand the r...

   GOLANG,SLICE,SLICE POINTER     2020-12-13 06:11:14

  Service discovery with etcd

In previous post, we have talked about etcd and its usage. This post we will cover how to implement server discovery with etcd. Service discovery is to solve one of the most commonly seen scenarios in distributed system where how to find the corresponding target service to talk to. In short, it is to find some server which one can talk to based on some service name. A complete service discovery system include below three key functions: Service registration: A service must register itself to so...

   ETCD,SERVICE DISCOVERY,DEMO,TUTORIAL     2021-03-08 05:36:29

  Custom C++ exception class creation

In standard C++, we can use try catch to catch and exception when something goes wrong. These are some built in exception support in C++. By including the #include , we can now catch exceptions in C++ programs. This actually helps us on debugging our code and reduce the maintenance work.However sometimes if we want to create our own custom exception class. What should we do?We should include the #include line and then extend the exception class and implement some methods as you like. The genera...

   C++,std,exception,custom exception,implementation     2012-03-04 09:58:18

  String.length() vs String.getBytes().length in Java

In Java, String.length() is to return the number of characters in the string, while String.getBytes().length is to return the number of bytes to represent the string with the specified encoding. By default, the encoding will be the value of system property file.encoding, the encoding name can be set manually as well by calling System.setProperty("file.encoding", "XXX"). For example, UTF-8, Cp1252. In many cases, String.length() will return the same value as String.getBytes().length, but in some ...

   Java,UTF8,String,Encoding,Sample     2015-04-01 22:22:23

  Recursive class initialization in Java

When a Java class is referenced and initialized, it has to go through the loading and linking first. Once the loading and linking complete successfully. The class will be initialized. The static variables and constant variables will be initialized during this process. Once the class is initialized, it is ready for use. If when class A is initialized and it is referencing a class B, the class B will also get initialized. But what will happen if class B is referencing class A as well? This is call...

   Java,JVM,class initialization,static final     2015-04-15 21:04:29

  OpenLDAP Proxy -- rwm-map vs map

OpenLDAP proxy is used to proxy ldap request and response between clients and servers, different servers may have different representations/attributes to mean the same thing. For example, in one LDAP server, the firstName may be represented by firstName, it may be represented by givenName in a different server. However, from the client perspective, it only wants to get the firstName, it doesn't care about the backend attributes. In this case, attribute mapping can help provide a virtual view of ...

   MAP,OPENLDAP,OPENLDAP PROXY,LDAP,RWM-MAP     2018-02-02 20:36:02

  The Greatest Regex Trick Ever (Simplified)

There is a post which is really hot recently which showcased a best ever regular expression trick. In this post, it provides a trick which can be adapted to situations where one wants to match some patterns desired and exclude the patterns undesired. In simple, the trick is : Pattern not desired | (Pattern desired) Then taking the group 1 match of the capturing group of matched. This group will contain the strings matching the desired patterns. Have to say this trick is really neat and brilliant...

   REGULAR EXPRESSION,PROGRAMMING,JAVA     2015-10-01 21:59:05

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