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  Understanding abstract interface in Java

Have you read about an interface declaration as public abstract interface InterfaceName in Java? At the first glance, is it a weird declaration? Why should we declare an interface as abstract? For example, we may see below code in some projects: public abstract interface MyInterface { public void check(); public abstract boolean check(boolean really); } Actually here abstract is redundant, an interface is implicitly abstract, we no need to put an abstract in front of interface. But it do...

   Java,abstract interface     2014-08-18 23:07:27

  Fastjson just fixed a bug which might cause out of memory issue

Fastjson just fixed a bug which might cause service down a few days ago. This bug is caused by some mishandling of special character \x which is an escaped character to indicate hexdecimal number. The impact of this bug would be big if the attacker constructs a malicious data which would cause the service down.  The code which causes the issue is in com.alibaba.fastjson.parser.JSONLexerBase#scanString, when a JSON string is passed in, fastjson would parse the string character by c...

   FASTJSON,ALIBABA,BUG,NEWS     2019-09-07 06:03:49

  Finding selected checkbox items in a JSF dataTable

This is one of those problems that I couldn’t find a complete example for when I needed it, so hopefully this will save somebody else the extra time it took me to piece it together. We frequently need to have data tables in our UI, and allow the user to select a subset of those items for action. In JavaServer Faces, this means having a DataTable, each row having its own checkbox. But when the action is triggered, how to we find which items the user has selected. The first step is to ...

   JavaServer Faces,JSF,Datatable,Checkbox,Example     2012-01-03 03:02:46

  Can a == true && a == false be true in JavaScript?

JavaScript is a weak typed language and it has a loose comparison feature where two objects/values of different type can be compared using == operator. This provides developers great flexibility and confusion at the same time.  Before understanding how == works in JavaScript, can you first answer the question in the post title? Can a == true && a == false be true in JavaScript? Normally, we would think that this expression will always return false since a can be either true or ...

   JAVASCRIPT,COMPARISON,INTERVIEW QUESTION,==     2018-03-25 03:39:43

  Arrays.equals() vs MessageDigest.isEqual()

Both Arrays.equals() and MessageDigest.isEqual() are used to compare the equality of two arrays. They can be interchangeably in many cases. However, they do have some differences which lead to different use cases in real applications. One difference is that the arrays passed to MessageDigest.isEqual() cannot be null while it's ok for Arrays.equals(). The one major difference between these two methods is that Arrays.equals() is not time-constant while MessageDigest.isEqual() is time-constant. Thi...

   Arrays.equal(),MessageDigest.isEqual(),Java,Security     2015-05-14 22:03:29

  A return to good code

Stop doing this:public boolean foo() { if (true) {   return true;   }  else {   return false;   }}It always amazes me when I dig into an open source project, and I see code written by supposed experts, and reviewed by seasoned professionals, and nobody slaps the wrists of the developer who shoves return statements right in the middle of a method.Tell me, how hard is it to do this:public boolean foo() {   boolean flag = true;  ...

   Java,Code,Method,Return,Condition     2011-03-23 01:24:47

  Deep clone of JavaScript object

In JavaScript world, it's frequently seen object clone. Normally when creating a clone of an object, it's only the reference being cloned but not all contents. In some scenarioes, it's desired to clone all the content instead of just the reference such that any change made to the cloned object will not change the original object. Differences between shallow clone and deep clone can be as simple as: Shallow clone : Only the object reference is cloned but not the content Deep clone : Clone all co...

   JAAVSCRIPT,DEEP CLONE,DEEP COPY,SHALLOW CLONE,SHALLOW COPY     2016-10-31 00:27:24

  When will resizing be triggered in Java HashMap?

HashMap is one of the most frequently used collection types in Java, it stores key-value pairs. Ideally it expects to use hash table which expects the data access time complexity to be O(1), however, due to hash conflicts, in reality, it uses linked list or red-black tree to store data which makes the worst case time complexity to be O(logn).  Although collections are using data structures like arrays and linked lists, unlike arrays, they will dynamically resize when there is not enough spa...

   JAVA,RESIZE,HASHMAP,THRESHOLD     2020-05-02 20:41:19

  Add ContextMenu to a customized View in Android

In Android, we may sometimes need to add ContextMenu to a View, it's not so easy to add ContextMenu to a customized View. Here we explain how to add ContextMenu to a customized View. First, we may need to create View.OnCreateContextMenuListener so that the customized view can register for it. Here is the class definition: public class GraphView extends View {     private View.OnCreateContextMenuListener vC = new View.OnCreateContextMenuListener() {       &...

   Android, ContextMenu,Customized view     2012-11-04 07:10:40

  JavaScript finite state machine

Finite state machine is a very useful design model, it can be used to simulate many events in the world. In short, finite state machine has three features: Number of states is finite At any moment, one object can only be in one state In some condition, it will transfer from one state to another state In JavaScript, finite state machine can be applied in many places. For example, one menu element on a webpage. When the mouse hovers on the menu, the menu will show up, while the mouse moves away...

   JavaScript,Finite state machine,State     2013-09-02 11:00:57

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