problems on inheritance in java

I. INTRODUCTIONThe BOM (byte order mark)---the byte sequence mark.Software such as Windows-brought Notepad, when saving a UTF-8 encoded file, inserts three invisible characters (0xEF 0xBB 0xBF, or BOM) where the file begins. It is a string of hidden characters that allows editors such as Notepad to identify whether the file is encoded in UTF-8. Windows uses a BOM to mark the way a text file is encoded.When you save a text file in UTF-8 format using a program such as Notepad, Notepad adds several

the way to communicate between threads through shared memory, so thread synchronization problems follow.2, Reorder:In order to make the operating unit within the processor as fully utilized as possible, the processor may perform a random order optimization of the input code, and the processor will reorganize the results of the sequence execution after the calculation, ensuring that the result is consistent with the sequential execution, but does not

+ */ surveytoken.unbind (); the return(surveyid%2) ==0? " Even ":" Odd ";//Returns the even string if it is an even number, or odd string if it is an odd number * } $SYSTEM.OUT.PRINTLN ("Survey object is empty");Panax Notoginseng return NULL; - } the +}The policy of the routed data source is determined in the overridden method: If the survey ID is even, it is saved to the answer table in the main library Lsn_surveypark, and if it is odd, it is

single.class.Some people say getclass can not do, this can't. It's one thing to write This.getclass. Because the GetClass method is non-static.Is there a difference between a synchronous code block and a sync function? No difference, after the thread comes in, still want to judge the lock, synchronized (Single.class).Now modify the program,The equivalent of the decision to determine the lock before the first step to determine the screening.How do you understand it? The video is designed so that

Understanding from the ground up java-17.4 detailed explanation synchronization (1)-problems caused by competition conditions In this chapter, we will discuss some synchronization topics and problems caused by competition conditions. 1. What are the competitive conditions? When multiple threads or processes read and write a shared data, the result depends on the

(NewString (bytes,0, Len)); - } - inputstream.close (); - response.getwriter (). Write (sb.tostring ()); + } - +}The following methods are available for loading a resource file in a Web project:Request object. Getrealpath ("/web-inf/classes/demo.txt"); A string that returns the absolute path of the file, but removed after the Java Servlet API 2.1 release, deprecatedThe context object. getResourceAsStream ("/web-inf/classes/demo.txt"); /

Polyconstructors {public static void Main (string[] args) { new roundglyph (5);} }Output Result:Glyph () before Draw () Roundglyph.draw (), Radius=0glypy () after draw () roundglyph.roundglyph,radius= 5This begs the question of an initialization order, and for an inherited situation, it is clear that the parent class is initialized first, and then the child class. Coupled with static properties, static blocks, and non-static properties, the order of construction methods.So if there

First, we need to figure out that in Java, references and basic data types are stored in the stack. The objects are stored in the heap.There is only one exception, the string object.For example:String str1= "Test"; String str2= "Test"; String Str3=new string ("Test1"); String Str4=new string ("Test1"); System.out.println (STR1==STR2); System.out.println (STR3==STR4);For STR1 and str2, the object "test" they refer to is neither in the stack nor in the

the same name masking.After-school Practice II:Write a program, the user input two number, to find out its subtraction, and the message box to display the calculation results.1. Source code:mao2015.10.7Two-digit operation in the form of a dialog boxImport Javax.swing.JOptionPane;public class Twonums {public static void Main (string[] args) {TODO auto-generated Method StubString num1,num2;int number1,number2;int add,minus,mul,div;NUM1 = Joptionpane.showinputdialog("Input the first integer please

Java.awt.event.mouseevent;import Java.awt.event.mousemotionadapter;import Java.awt.event.windowadapter;import Java.awt.event.WindowEvent;import javax.swing.jlayeredpane;//applet to implement mouse Move component public class Parentandchild {static point oldpt;static jlayeredpane pane = new JLayeredPane (); static button btn = New button (), btn1 = New button ("giggle");p ublic static void Main (string[] args) {Frame fm = new Frame ("hahaha"), fm.setvisible (True);p ane.setlayout (New FlowLayou

a xbean.jar is the correct version, this time I know it might be a jar package conflict, but at this point on the structure of the Web project is not very clear, why in the test class is not a problem, but why in the Web run when the exception is generated, the reason, here to understand, run under the web time, under the Webroot under the web-inf below the Lib Jar is the project run time used to use the jar, so I went to find, sure enough to find a Xbean.jar and

().getRealPath("/up");DiskFileItemFactory disk = new DiskFileItemFactory(1024*10,new File("d:/a"));ServletFileUpload up = new ServletFileUpload(disk);try{List//只接收图片*.jpg-iamge/jpege.,bmp/imge/bmp,png,Listnew ArrayListfor(FileItem file :list){if(file.getContentType().contains("image/")){String fileName = file.getName();fileName = fileName.substring(fileName.lastIndexOf("\\")+1);//获取扩展String extName = fileName.substring(fileName.lastIndexOf("."));//.jpg//UUIDString uuid = UUID.randomUUID().toStri

Application Scenario Description:Java Web program, triggering the call C # written in the background EXE program, found in the EXE written files cannot be found. Execute the exe under the cmd command line alone no problem;Problem Lookup:Because EXE gets the file path error caused;Workaround:EXE in the Get program path instead:String pathlog = System.Reflection.Assembly.GetExecutingAssembly (). Location;Pathlog = pathlog.substring (0, Pathlog.lastindexof (@ "\")) + "/log.txt";Appendix:

Today in the use of Android studio to hit the code to find that the console out of Chinese characters, a dozen Chinese characters are all garbled. This special solution.Add the following code under the Java Project Catalog Build.gradle:1. New GradleTasks.withtype (javacompile) { options.encoding = "UTF-8"}2. Old version GradleTasks.withtype (Compile) { options.encoding = "UTF-8"}　Garbled problems in t

to read B.length bytes, and the reality is that the system is often not read so much. A closer look at the Java API description reveals that this method does not guarantee that you can read so many bytes, it can only guarantee to read so many bytes (at least 1). Therefore, if you want a program to read count bytes, it is best to use the following code:Byte[] B = new Byte[count];int readcount = 0; The number of bytes that have been successfully readwh

1. Importing SQL Package errorsWorkaround:Click Project Right-click Properties->java Build path-> libraries->jre System library–> EditSelect Workspace Default Jre->finish2. Import Javax.servlet Package ErrorWorkaround:Properties->java Build path->libraries->add libraries->server Runtime, select Tomcat Server3, run time-out, and even if the context to modify the longer time is the same result, I was in this

(); byte[] bytes4 = S.getbytes ("Utf-16be"); //utf-8 Code Chinese occupies 3 bytes, English occupies 1 bytes for(byteb:bytes4) { //converts bytes to int to be displayed in 16 binary modeSystem.out.print (integer.tohexstring (BAMP;0XFF) + ""); } System.out.println (); /** When your byte sequence is some kind of encoding, this time you want to turn the byte sequence into a * string, also need to use this encoding method, no one will appear garbled*/String str1=NewString

1 Fail-fast IntroductionThe fail-fast mechanism is an error mechanism in the Java Collection (Collection). Fail-fast events can occur when multiple threads operate on the contents of the same collection.For example, when a thread A is traversing a collection through iterator, if the contents of the collection are changed by another thread, thread a accesses the collection and throws an Concurrentmodificationexception exception, resulting in a fail-fas

= M.getgenericparametertypes ();class[] classes = M.getparametertypes ();int i = 0;For (Type c:types) {int index = i++;String arg = Args[index];if (! ( C instanceof Parameterizedtype)) {String jsonstr = json.objtostr (ARG);Arglist.add (Json.strtoobj (Jsonstr,classes[index));continue; } Parameterizedtype pt = (parameterizedtype) C;Objectmapper mapper = new Objectmapper ();class[] genericclazzes = new class[pt.getactualtypearguments (). length];int j = 0;For (Type type:pt.getActualTypeArguments

Coding | solving | problems | Chinese code Message headers (see rfc822,rfc2047) can contain only us-ascii characters. Any part of the message header that contains a US-ASCII character must be encoded so that it contains only us-ascii characters. Therefore, the use of Java mail to send Chinese mail must be encoded, or others receive your mail can only be garbled a bunch. The solution to the