Java-Tricky-Tech-Questions.md

What is the difference between Serializable and Externalizable in Java?

  • In earlier version of Java, reflection was very slow, and so serializaing large object graphs (e.g. in client-server RMI applications) was a bit of a performance problem. To handle this situation, the java.io.Externalizable interface was provided, which is like java.io.Serializable but with custom-written mechanisms to perform the marshalling and unmarshalling functions (you need to implement readExternal and writeExternal methods on your class). This gives you the means to get around the reflection performance bottleneck.
  • In recent versions of Java (1.3 onwards, certainly) the performance of reflection is vastly better than it used to be, and so this is much less of a problem. I suspect you’d be hard-pressed to get a meaningful benefit from Externalizable with a modern JVM.
  • Also, the built-in Java serialization mechanism isn’t the only one, you can get third-party replacements, such as JBoss Serialization, which is considerably quicker, and is a drop-in replacement for the default.
  • A big downside of Externalizable is that you have to maintain this logic yourself - if you add, remove or change a field in your class, you have to change your writeExternal/readExternal methods to account for it.
  • In summary, Externalizable is a relic of the Java 1.1 days. There’s really no need for it any more.

write transcient fields

  • Storing and reconstituting the transient data can also be achieved by implementing the Externalizable interface and implementing the writeExternal( ) and the readExternal( ) methods of that interface.

Java Class

  • Class objects for known types can also be written as “class literals”: 
    // Express a class literal as a type name followed by ".class"
c = int.class; // Same as Integer.TYPE
c = String.class; // Same as "a string".getClass()
c = byte[].class; // Type of byte arrays
  • For primitive types and void, we also have class objects that are represented as literals: 
    // Obtain a Class object for primitive types with various 
// predefined constants
c = Void.TYPE; // The special "no-return-value" type
c = Byte.TYPE; // Class object that represents a byte
c = Integer.TYPE; // Class object that represents an int
c = Double.TYPE; // etc; see also Short, Character, Long, Float

Convert arrays to ArrayList, two different approaches

// View array as an ungrowable list List l = Arrays.asList(a); // Make a growable copy of the view List m = new ArrayList(l);

What’s seed in Java

Since the next number in a pseudorandom generator is determined by the pre- vious number(s), such a generator always needs a place to start, which is called its seed. The sequence of numbers generated for a given seed will always be the same. The seed for an instance of the java.util.Random class can be set in its constructor or with its setSeed() method.

Cipher

  • Given a variable c that is known to be an uppercase letter, the Java computation, j = c − ‘A’ produces the desired index j. As a sanity check, if character c is ‘A’, then j = 0. When c is ‘B’, the difference is 1.

Uncaught exception handler

  • The Thread API also provides the UncaughtExceptionHandler facility, which lets you detect when a thread dies due to an uncaught exception. The two approaches are complementary: taken together, they provide defense-in- depth against thread leakage.
  • When a thread exits due to an uncaught exception, the JVM reports this event to an application-provided UncaughtExceptionHandler (see Listing 7.24); if no handler exists, the default behavior is to print the stack trace to System.err
  • In long-running applications, always use uncaught exception handlers for all threads that at least log the exception.
  • To set an UncaughtExceptionHandler for pool threads, provide a ThreadFac- tory to the ThreadPoolExecutor constructor.
  • Somewhat confusingly, exceptions thrown from tasks make it to the uncaught exception handler only for tasks submitted with execute ; for tasks submitted with submit, any thrown exception, checked or not, is considered to be part of the task’s return status. If a task submitted with submit terminates with an exception, it is rethrown by Future.get, wrapped in an ExecutionException. 
    public class UEHLogger implements Thread.UncaughtExceptionHandler{
public void uncaughtException(Thread t, Throwable e){
  Logger logger=Logger.getAnonymousLogger();
  logger.log(Level.SEVERE, "Thread terminated with exception:"+e.getName(),e);
}
}

What is the difference between Iterator and Enumeration

  • Iterator duplicate functionality of Enumeration with one addition of remove() method
  • Another difference is that Iterator is more safe than Enumeration and doesn’t allow another thread to modify collection object during iteration except remove() method and throws ConcurrentModificaitonException.

How does HashSet is implemented in Java, How does it use Hashing

  • HashSet is built on top of HashMap. If you look at source code of java.util.HashSet class, you will find that that it uses a HashMap with same values for all keys, as shown below: 
    private transient HashMap map;
// Dummy value to associate with an Object in the backing Map
private static final Object PRESENT = new Object();
// When you call add() method of HashSet, it put entry in HashMap :
public boolean add(E e) {
return map.put(e, PRESENT)==null;
}

    What do you need to do to use a custom object as a key in Collection classes like Map or Set? (answer)

  • If you are using any custom object in Map as key, you need to override equals() and hashCode() method, and make sure they follow their contract.
  • On the other hand if you are storing a custom object in Sorted Collection e.g. SortedSet or SortedMap, you also need to make sure that your equals() method is consistent to compareTo() method, otherwise that collection will not follow there contacts e.g. Set may allow duplicates.

Java Generics ? , E and T what is the difference?

Well there’s no difference between the first two - they’re just using different names for the type parameter (E or T).

The third isn’t a valid declaration - ? is used as a wildcard which is used when providing a type argument, e.g. List<?> foo = … means that foo refers to a list of some type, but we don’t know what.

Question: What does the following Java program print?

public class Test { public static void main(String[] args) { System.out.println(Math.min(Double.MIN_VALUE, 0.0d)); } }

Anwser 0.0d

The Double.MIN_VALUE is 2^(-1074), a double constant whose magnitude is the least among all double values.

What will happen if you put return statement or System.exit () on try or catch block? Will finally block execute?

Answer of this tricky question in Java is that finally block will execute even if you put a return statement in the try block or catch block but finally block won’t run if you call System.exit() from try or catch block.

Question: Can you override a private or static method in Java?

Another popular Java tricky question, As I said method overriding is a good topic to ask trick questions in Java. Anyway, you can not override a private or static method in Java, if you create a similar method with same return type and same method arguments in child class then it will hide the superclass method, this is known as method hiding.

Similarly, you cannot override a private method in sub class because it’s not accessible there, what you do is create another private method with the same name in the child class. See Can you override a private method in Java or more details

Question: What do the expression 1.0 / 0.0 will return? will it throw Exception? any compile time error?

Answer: This is another tricky question from Double class. Though Java developer knows about the double primitive type and Double class, while doing floating point arithmetic they don’t pay enough attention to Double.INFINITY , NaN, and -0.0 and other rules that govern the arithmetic calculations involving them. The simple answer to this question is that it will not throw ArithmeticExcpetion and return Double.INFINITY.

Also, note that the comparison x == Double.NaN always evaluates to false, even if x itself is a NaN. To test if x is a NaN, one should use the method call Double.isNaN(x) to check if given number is NaN or not. If you know SQL, this is very close to NULL there.

Overloading vs Overriding

  • Main difference comes from the fact that method overloading is resolved during compile time, while method overriding is resolved at runtime
  • Also rules of overriding or overloading a method are different in Java.
    • a private, static and final method cannot be overriding in Java but you can still overload them
    • overriding both name and signature of the method must remain same, but in for overloading method, the signature must be different
    • call to overloaded methods are resolved using static binding while the call to overridden method is resolved using dynamic binding in Java.
  • Java programmer to declare method with same name but different behavior. Method overloading and method overriding is based on Polymorphism in Java.
  • In case of method overloading, method with same name co-exists in same class but they must have different method signature, while in case of method overriding, method with same name is declared in derived class or sub class
  • If you have two methods with same name in one Java class with different method signature than its called overloaded method in Java. You can also overload constructor in Java
  • Since return type is not part of method signature simply changing return type will result in duplicate method and you will get compile time error in Java.
  • you can also overload private and final method in Java but you can not override them
  • When you override a method in Java its signature remains exactly same including return type. Rules of override:
    • Method signature must be same including return type, number of method parameters, type of parameters and order of parameters . Be advised: as of Java 5, you’re allowed to change the return type in the overriding method as long as the new return type is a subtype of the declared return type of the overridden (super class) method
    • Overriding method can not throw higher Exception than original or overridden method. means if original method throws IOException than overriding method can not throw super class of IOException e.g. Exception but it can throw any sub class of IOException or simply does not throw any Exception. This rule only applies to checked Exception in Java, overridden method is free to throw any unchecked Exception.
    • Overriding method can not reduce accessibility of overridden method , means if original or overridden method is public than overriding method can not make it protected.
  • Another important point is that you can not override static method in Java because they are associated with Class rather than object and resolved and bonded during compile time and that’s the reason you cannot override main method in Java
  • From Java 5 onwards you can use annotation in Java to declare overridden method just like we did with @override. ** @override annotation allows compiler** , IDE like NetBeans and Eclipse to cross verify or check if this method is really overrides super class method or not.

Static vs. Dynamic binding

  • private, final and static methods and variables uses static binding and bonded by compiler while virtual methods are bonded during runtime based upon runtime object.
  • Here is sample of static binding 
    public class StaticBindingTest {
    public static void main(String args[])  {
     Collection c = new HashSet();
     StaticBindingTest et = new StaticBindingTest();
     et.sort(c);
        }
   
  //overloaded method takes Collection argument
  public Collection sort(Collection c){
      System.out.println("Inside Collection sort method");
      return c;
  }

 //another overloaded method which takes HashSet argument which is sub class
  public Collection sort(HashSet hs){
      System.out.println("Inside HashSet sort method");
      return hs;
  }
    }
Output: Inside Collection sort method

    because it was bonded on compile time based on type of variable (Static binding) which was collection.

  • Here is sample of dynamic binding ```java public class DynamicBindingTest { public static void main(String args[]) { Vehicle vehicle = new Car(); //here Type is vehicle but object will be Car vehicle.start(); //Car’s start called because start() is overridden method } }

class Vehicle { public void start() { System.out.println(“Inside start method of Vehicle”); } }

class Car extends Vehicle { @Override public void start() { System.out.println(“Inside start method of Car”); } }

Output: Inside start method of Car


In summary, bottom line is static binding is a compile time operation while dynamic binding is a runtime. one uses Type and other uses Object to bind. static, private and final methods and variables are resolved using static binding which makes there execution fast because no time is wasted to find correct method during runtime.

# Static in Java
- static keyword can not be applied on top level class. Making a top level class static in Java will result in compile time error.
-  Beware that if your static initialize block throws Exception than you may **get java.lang.NoClassDefFoundError** when you try to access the class which failed to load.
-  **Static method can not be overridden** in Java as they belong to class and not to object
```java
 public class TradingSystem {

    public static void main(String[] args) {
        TradingSystem system = new DirectMarketAccess();
        DirectMarketAccess dma = new DirectMarketAccess();
        
        // static method of Instrument class will be called,

        // even though object is of sub-class DirectMarketAccess
        system.printCategory();
        
        //static method of EquityInstrument class will be called
        dma.printCategory();
    }

    public static void printCategory(){
        System.out.println("inside super class static method");
    }
}

class DirectMarketAccess extends TradingSystem{
    public static void printCategory(){
        System.out.println("inside sub class static method");
    }
}

Output:
inside super class static method
inside sub class static method
  • This shows that static method can not be overridden in Java and concept of method overloading doesn’t apply to static methods. Instead declaring same static method on Child class is known as method hiding in Java
  • Consider making a static variable final in Java to make it constant and avoid changing it from anywhere in the code
  • when to use Singleton vs Static Class in Java for those purpose,answer is that if its completely stateless and it work on provided data then you can go for static class otherwise Singleton pattern is a better choice.

    When to make a method static in Java

  • Method doesn’t depends on object’s state, in other words doesn’t depend on any member variable and everything they need is passes as parameter to them
  • Utility methods are good candidate of making static in Java because then they can directly be accessed using class name without even creating any instance. Classic example is java.lang.Math
  • Static method in Java is very popular to implement Factory design pattern. Since Generics also provides type inference during method invocation, use of static factory method to create object is popular Java idiom.

Phone

  • Key to success in telephonic is to the point and concise answer.

Difference between String, StringBuffer and StringBuilder in Java

  • String is immutable while both StringBuffer and StringBuilder is mutable, which means any change e.g. converting String to upper case or trimming white space will produce another instance rather than changing the same instance. On later two, StringBuffer is synchronized while StringBuilder is not, in fact its a ditto replacement of StringBuffer added in Java 1.5.

    Difference between extends Thread vs implements Runnable in Java?

  • Difference comes from the fact that you can only extend one class in Java, which means if you extend Thread class you lose your opportunity to extend another class, on the other hand if you implement Runnable, you can still extend another class.

Difference between Runnable and Callable interface in Java?

  • Runnable was the only way to implement a task in Java which can be executed in parallel before JDK 1.5 adds Callable. Just like Runnable, Callable also defines a single call() method but unlike run() it can return values and throw exceptions.

Difference between ArrayList and LinkedList in Java?

  • In short, ArrayList is backed by array in Java, while LinkedList is just collection of nodes, similar to linked list data structure. ArrayList also provides random search if you know the index, while LinkedList only allows sequential search. On other hand, adding and removing element from middle is efficient in LinkedList as compared to ArrayList because it only require to modify links and no other element is rearranged.

What is difference between wait and notify in Java?

  • Both wait and notify methods are used for inter thread communication, where wait is used to pause the thread on a condition and notify is used to send notification to waiting threads. Both must be called from synchronized context e.g. synchronized method or block.

Difference between HashMap and Hashtable in Java?

  • Though both HashMap and Hashtable are based upon hash table data structure, there are subtle difference between them. HashMap is non synchronized while Hashtable is synchronized and because of that HashMap is faster than Hashtable, as there is no cost of synchronization associated with it. One more minor difference is that HashMap allows a null key but Hashtable doesn’t.

Check a number is prime or not

  • We learned numbers are prime if the only divisors they have are 1 and itself. Trivially, we can check every integer from 1 to itself (exclusive) and test whether it divides evenly. Check the source code of ** PrimeTester.java**
    • naive approach: We learned numbers are prime if the only divisors they have are 1 and itself. Trivially, we can check every integer from 1 to itself (exclusive) and test whether it divides evenly. 
       for(int i=2;2*i<=n;i++){
       if(n%i==0)
    • power of 2 approach: further enhance, as if 2 divides some interger n, then (n/2) divides n as well so we’ll times of 2. Please be advised in for loop, should use 2*i<=n, rather than “<n”, otherwise, 4 will be return as ture mistakely 
       for(int i=2;2*i<=n;i++){
       if(n%i==0)
    • isPrimeSquare approach: we notice that you really only have to go up to the square root of n, because if you list out all of the factors of a number, the square root will always be in the middle Finally, we know 2 is the “oddest” prime - it happens to be the only even prime number. Because of this, we need only check 2 separately, then traverse odd numbers up to the square root of n. In the end, our code will resemble this: 
       // check if n is a multiple of 2
 if(n>2&&n%2==0)
       return false;		
   // if not, then just check the odds
   for(int i=3;i*i<=n;i+=2){
       if(n%i==0)

      Difference between abstract class and interface?

  • From Java 8 onwards difference between abstract class and interface in Java has minimized, now even interface can have implementation in terms of default and static method. BTW, in Java you can still extend just one class but can extend multiple inheritance. Abstract class is used to provide default implementation with just something left to customize, while interface is used heavily in API to define contract of a class.

How to Swap Two Numbers without Temp or Third variable in Java

Swapping two numbers without using temp variable in Java

int a = 10;
int b = 20;
System.out.println("value of a and b before swapping, a: " + a +" b: " + b);

//swapping value of two numbers without using temp variable
a = a+ b; //now a is 30 and b is 20
b = a -b; //now a is 30 but b is 10 (original value of a)
a = a -b; //now a is 20 and b is 10, numbers are swapped

System.out.println("value of a and b after swapping, a: " + a +" b: " + b);
Output:
value of a and b before swapping, a: 10 b: 20
value of a and b after swapping, a: 20 b: 10

Swapping two numbers without using temp variable in Java with bitwise operator

int a = 2; //0010 in binary
int b = 4; //0100 in binary
System.out.println("value of a and b before swapping, a: " + a +" b: " + b);
// 6  is     0110
//swapping value of two numbers without using temp variable and XOR bitwise operator     
a = a^b; //now a is 6 (0110) and b is 4(0100)
b = a^b; //now a is 6 but b is 2 (0010) (original value of a)
a = a^b; //now a is 4 and b is 2, numbers are swapped

System.out.println("value of a and b after swapping using XOR bitwise operation, a: " + a +" b: " + b);
value of a and b before swapping, a: 2 b: 4
value of a and b after swapping using XOR bitwise operation, a: 4 b: 2

Swapping two numbers without using temp variable in Java with division and multiplication

  • There is another, third way of swapping two numbers without using third variable, which involves multiplication and division operator. ```java int a = 6; int b = 3; System.out.println(“value of a and b before swapping, a: “ + a +” b: “ + b);

//swapping value of two numbers without using temp variable using multiplication and division a = a*b; //now a is 18 and b is 3 b = a/b; //now a is 18 but b is 6 (original value of a) a = a/b; //now a is 3 and b is 6, numbers are swapped

System.out.println(“value of a and b after swapping using multiplication and division, a: “ + a +” b: “ + b); Output: value of a and b before swapping, a: 6 b: 3 value of a and b after swapping using multiplication and division, a: 3 b: 6 ```

  • That’s all on 3 ways to swap two variables without using third variable in Java. Its good to know multiple ways of swapping two variables without using temp or third variable to handle any follow-up question. Swapping numbers using bitwise operator is the fastest among three, because it involves bitwise operation. It’s also great way to show your knowledge of bitwise operator in Java and impress interviewer, which then may ask some question on bitwise operation. A nice trick to drive interview on your expert area.

Bitwise operator

  • ”~” inverts a bit pattern; it can be applied to any of the integral types, making every “0” a “1” and every “1” a “0”.
  • The bitwise & operator performs a bitwise AND operation.
  • The bitwise ^ operator performs a bitwise exclusive OR operation.
  • The bitwise operator performs a bitwise inclusive OR operation.

How to check if linked list contains loop in Java?

  • Algorithm to find if linked list contains loops or cycles. Two pointers, fast and slow is used while iterating over linked list. Fast pointer moves two nodes in each iteration, while slow pointer moves to one node. If linked list contains loop or cycle than both fast and slow pointer will meet at some point during iteration. If they don’t meet and fast or slow will point to null, then linked list is not cyclic and it doesn’t contain any loop.
    1. Use two pointers fast and slow
    2. Move fast two nodes and slow one node in each iteration
    3. If fast and slow meet then linked list contains cycle
    4. if fast points to null or fast.next points to null then linked list is not cyclic
  • This algorithm is also known as Floyd’s cycle finding algorithm and popularly known as tortoise and hare algorithm to find cycles in linked list. Sample can be found via “LoopInList.java”

Reference

  • http://www.java67.com/2012/09/top-10-tricky-java-interview-questions-answers.html
  • http://javarevisited.blogspot.in/2012/03/what-is-static-and-dynamic-binding-in.html
  • http://www.java67.com/2015/03/top-40-core-java-interview-questions-answers-telephonic-round.html
  • http://www.mkyong.com/java/how-to-determine-a-prime-number-in-java/
  • http://javarevisited.blogspot.in/2013/02/swap-two-numbers-without-third-temp-variable-java-program-example-tutorial.html
  • http://docs.oracle.com/javase/tutorial/java/nutsandbolts/op3.html
  • http://javarevisited.blogspot.in/2013/05/find-if-linked-list-contains-loops-cycle-cyclic-circular-check.html

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2018

Seconds

less than 1 minute read

nano seconds

Citrix receiver

less than 1 minute read

“Cannot connect to remote desktop” with Citrix Receiver

Guice

7 minute read

A new type of Juice Put simply, Guice alleviates the need for factories and the use of new in your Java code. Think of Guice’s @Inject as the new new. You wi...

YAML

less than 1 minute read

Key points All YAML files (regardless of their association with Ansible or not) can optionally begin with — and end with …. This is part of the YAML format a...

Mockito

less than 1 minute read

Feature

Protobuf

5 minute read

What are protocol buffers?

Sudo in a Nutshell

6 minute read

Sudo in a Nutshell Sudo (su “do”) allows a system administrator to give certain users (or groups of users) the ability to run some (or all) commands as root...

Zoo-keeper

15 minute read

ZK Motto the motto “ZooKeeper: Because Coordinating Distributed Systems is a Zoo.”

Cucumber

28 minute read

Acceptance testing vs unit test It’s sometimes said that unit tests ensure you build the thing right, whereas acceptance tests ensure you build the right thi...

Scala

less than 1 minute read

Scala String

akka framework of scala

27 minute read

philosophy The actor model adopts the philosophy that everything is an actor. This is similar to the everything is an object philosophy used by some object-o...

Apache Camel

8 minute read

Camel’s message model In Camel, there are two abstractions for modeling messages, both of which we’ll cover in this section. org.apache.camel.Message—The ...

JXM

less than 1 minute read

Exporting your beans to JMX The core class in Spring’s JMX framework is the MBeanExporter. This class is responsible for taking your Spring beans and registe...

Solace MQ

1 minute read

Solace PubSub+ It is a message broker that lets you establish event-driven interactions between applications and microservices across hybrid cloud environmen...

Apigee

4 minute read

App deployment, configuration management and orchestration - all from one system. Ansible is powerful IT automation that you can learn quickly.

Ansible

11 minute read

Ansible: What Is It Good For? Ansible is often described as a configuration management tool, and is typically mentioned in the same breath as Chef, Puppet, a...

flexbox

4 minute read

How Flexbox works — explained with big, colorful, animated gifs

KDB

18 minute read

KDB However kdb+ evaluates expressions right-to-left. There are no precedence rules. The reason commonly given for this behaviour is that it is a much simple...

Portactor

1 minute read

Better to use smart wait

Agile and SCRUM

less than 1 minute read

Key concept In Scrum, a team is cross functional, meaning everyone is needed to take a feature from idea to implementation.

rxjs pipe in depth

6 minute read

https://stormforger.com/blog/2016/07/08/types-of-performance-testing/

Strategy-Of-Openshift-Releases

less than 1 minute read

Release & Testing Strategy There are various methods for safely releasing changes to Production. Each team must select what is appropriate for their own ...

NodeJs Notes

less than 1 minute read

commands to read files var lineReader = require(‘readline’).createInterface({ input: require(‘fs’).createReadStream(‘C:\dev\node\input\git_reset_files.tx...

Minium Viable Product

less than 1 minute read

https://blog.leanstack.com/minimum-viable-product-mvp-7e280b0b9418

CORS :Cross-Origin Resource Sharing

1 minute read

Cross-Origin Request Sharing - CORS (A.K.A. Cross-Domain AJAX request) is an issue that most web developers might encounter, according to Same-Origin-Policy,...

ngrx

2 minute read

Why @Effects? In a simple ngrx/store project without ngrx/effects there is really no good place to put your async calls. Suppose a user clicks on a button or...

iOS programming

3 minute read

View A view is also a responder (UIView is a subclass of UIResponder). This means that a view is subject to user interactions, such as taps and swipes. Thus,...

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2017

cloud computering

less than 1 minute read

openshift vs openstack The shoft and direct answer is `OpenShift Origin can run on top of OpenStack. They are complementary projects that work well together....

cloud computering

3 minute read

Concepts Cloud computing is the on-demand demand delivery of compute database storage applications and other IT resources through a cloud services platform v...

Redux

less than 1 minute read

whats @Effects You can almost think of your Effects as special kinds of reducer functions that are meant to be a place for you to put your async calls in suc...

reactive programing

less than 1 minute read

The second advantage to a lazy subscription is that the observable doesn’t hold onto data by default. In the previous example, each event generated by the in...

Container

2 minute read

The Docker project was responsible for popularizing container development in Linux systems. The original project defined a command and service (both named do...

promise vs observiable

less than 1 minute read

The drawback of using Promises is that they’re unable to handle data sources that produce more than one value, like mouse movements or sequences of bytes in ...

JDK source

less than 1 minute read

interface RandomAccess Marker interface used by List implementations to indicate that they support fast (generally constant time) random access. The primary ...

SSH SFTP

4 minute read

Secure FTP SFTP over FTP is the equivalant of HTTPS over HTTP, the security version

AWS Tips

less than 1 minute read

After establishing a SSH session, you can install a default web server by executing sudo yum install httpd -y. To start the web server, type sudo service htt...

Oracle

less than 1 minute read

ORA-12899: Value Too Large for Column

Spring notes

28 minute read

Spring Bean Life Cycle Callback Methods

Kindle notes

113 minute read

#《亿级流量网站架构核心技术》目录一览 TCP四层负载均衡 使用Hystrix实现隔离 基于Servlet3实现请求隔离 限流算法 令牌桶算法 漏桶算法 分布式限流 redis+lua实现 Nginx+Lua实现 使用sharding-jdbc分库分表 Disruptor+Redis...

Java Security Notes

8 minute read

Java Security well-behaved: programs should be prevent from consuming too much system resources

R Language

less than 1 minute read

s<-read.csv("C:/Users/xxx/dev/R/IRS/SHH_SCHISHG.csv") # aggregate s2<-table(s$Original.CP) s3<-as.data.frame(s2) # extract by Frequency ordered s3...

SSH and Cryptography

35 minute read

SFTP versus FTPS SS: Secure Shell An increasing number of our customers are looking to move away from standard FTP for transferring data, so we are ofte...

Eclipse notes

less than 1 minute read

How do I remove a plug-in? Run Help > About Eclipse > Installation Details, select the software you no longer want and click Uninstall. (On Macintosh i...

Java JVM

less than 1 minute read

Class loading subsystem

Maven-Notes

27 minute read

Maven philosophy “It is important to note that in the pom.xml file you specify the what and not the how. The pom.xml file can also serve as a documentatio...

Java New IO

less than 1 minute read

Notes JDK 1.0 introduced rudimentary I/O facilities for accessing the file system (to create a directory, remove a file, or perform another task), accessi...

IT-Architect

1 minute read

SOA SOA is a set of design principles for building a suite of interoperable, flexible and reusable services based architecture. top-down and bottom-up a...

Algorithm

14 minute read

This page is about key points about Algorithm

Java-Tricky-Tech-Questions.md

19 minute read

What is the difference between Serializable and Externalizable in Java? In earlier version of Java, reflection was very slow, and so serializaing large ob...

Compare-In-Java

6 minute read

Concepts If you implement Comparable interface and override compareTo() method it must be consistent with equals() method i.e. for equal object by equals(...

Java Collections Misc

3 minute read

Difference between equals and deepEquals of Arrays in Java Arrays.equals() method does not compare recursively if an array contains another array on oth...

HashMap in JDK

4 minute read

Hashmap in JDK Some note worth points about hashmap Lookup process Step# 1: Quickly determine the bucket number in which this element may resid...

Java 8 Tips

66 minute read

This blog is listing key new features introduced in Java 8

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2016

Java GC notes

28 minute read

verbose:gc verbose:gc prints right after each gc collection and prints details about each generation memory details. Here is blog on how to read verbose gc

Hash Code Misc

12 minute read

contract of hashCode : Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consis...

Angulary Misc

2 minute read

Dependency Injection Angular doesn’t automatically know how you want to create instances of your services or the injector to create your service. You must co...

Random number in java

less than 1 minute read

ThreadLocalRandom, SecureRandm, java.util.Random, java.math.Random

Java new features

less than 1 minute read

JDK Versions JDK 1.5 in 2005 JDK 1.6 in 2006 JDK 1.7 in 2011 JDK 1.8 in 2014 Sun之前风光无限，但是在2010年1月27号被Oracle收购。 在被Oracle收购后对外承诺要回到每2年一个realse的节奏。但是20...

Simpler chronicle of CI(Continuous Integration) “乱弹系列”之持续集成工具

less than 1 minute read

引言 有句话说有人的地方就有江湖，同样，有江湖的地方就有恩怨。在软件行业历史长河（虽然相对于其他行业来说，软件行业的历史实在太短了，但是确是充满了智慧的碰撞也是十分的精彩）中有一些恩怨情愁，分分合合的小故事，比如类似的有，从一套代码发展出来后面由于合同到期就分道扬镳，然后各自发展成独门产品的Sybase DB和微...

浅谈软件单元测试中的“断言” (assert)，从石器时代进步到黄金时代。

less than 1 minute read

大家都知道，在软件测试特别是在单元测试时,必用的一个功能就是“断言”（Assert)，可能有些人觉得不就一个Assert语句，没啥花头，也有很多人用起来也是懵懵懂懂，认为只要是Assert开头的方法，拿过来就用。一个偶然的机会跟人聊到此功能，觉得还是有必要在此整理一下如何使用以及对“断言”的理解。希望可以帮助大家...

Head First Blockchina 1

less than 1 minute read

深入浅出区块链系统：第一章. what you should know about blockchain

Kubernetes 与 Docker Swarm的对比

less than 1 minute read

Kubernetes 和Docker Swarm 可能是使用最广泛的工具，用于在集群环境中部署容器。但是这两个工具还是有很大的差别。

http methods

11 minute read

RFC origion http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.2)

Spark-vs-Storm

less than 1 minute read

The stark difference among Spark and Storm. Although both are claimed to process the streaming data in real time. But Spark processes it as micro-batches; wh...

微服务

less than 1 minute read

可以想像一下，之前的传统应用系统，像是一个大办公室里面，有各个部门，销售部，采购部，财务部。办一件事情效率比较高。但是也有一些弊端，首先，各部门都在一个房间里。

kibana, view layer of elasticsearch

less than 1 minute read

What’s Kibana kibana is an open source data visualization plugin for Elasticsearch. It provides visualization capabilities on top of the content indexed on...

kibana, view layer of elasticsearch

less than 1 minute read

What’s Kibana kibana is an open source data visualization plugin for Elasticsearch. It provides visualization capabilities on top of the content indexed on...

iConnect

less than 1 minute read

UI HTML5, AngularJS, BootStrap, REST API, JSON Backend Hadoop core (HDFS), Hive, HBase, MapReduce, Oozie, Pig, Solr

Business Analysis

less than 1 minute read

Purpose of BA 带来一些商业价值（收益） 解决业务痛点

Data Structure

2 minute read

Binary Tree A binary tree is a tree in which no node can have more than two children. A property of a binary tree that is sometimes important is that th...

equity trading

less than 1 minute read

Difference between mutal funds and hedge funds

SQL

less than 1 minute read

Differences between not in, not exists , and left join with null

HTTPS/2

less than 1 minute read

concepts

Github page commands notes

less than 1 minute read

404 error for customized domain (such as godday) 404 There is not a GitHub Pages site here. Go to github master branch for gitpages site, manually add CN...

RenMinBi International

1 minute read

RQFII RQFII stands for Renminbi Qualified Foreign Institutional Investor. RQFII was introduced in 2011 to allow qualified foreign institutional investors to ...

Load Balancing

less than 1 minute read

Concepts LVS means Linux Virtual Server, which is one Linux built-in component.

Python

less than 1 minute read

(‘—–Unexpected error:’, <type ‘exceptions.TypeError’>) datetime.datetime.now()

Setup Git in Mint Linux

less than 1 minute read

How to setup Git in Mint Linux =================================================

Microservices vs. SOA

1 minute read

Microservice Services are organized around capabilities, e.g., user interface front-end, recommendation, logistics, billing, etc. Services are small in ...

Java Class Loader

33 minute read

Codecache The maximum size of the code cache is set via the -XX:ReservedCodeCacheSize=N flag (where N is the default just mentioned for the particular com...

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