Java

In Java you will often see errors about null pointer exceptions, and it is difficult to find such errors, simply summarize.· Causes of NULL pointer exceptions:1, the string variable is not initialized. String Str. You create a null pointer exception

Request.setcharacterencoding ("Utf-8"); Response.setcontenttype ("Text/html;charset=utf-8");This is the code that sets the character encoding in the servlet, but usually there is more than one servlet, so we need to write the above code in every

Annotations are currently very popular, and many mainstream frameworks support annotations, and when you write your own code, you try to use annotations as much as possible, but the code is more concise.The syntax of annotations is simple, except

1) refer to the first group by \1public static void Main (string[] args) {String content= "hello world!"; String regextstr= ".*?"; Pattern pattern=pattern.compile (Regextstr, pattern.case_insensitive); Matcher Matcher =pattern.matcher (content), if

Using the class's static fields and constructors, we can track the number of objects created by a class. Write a class that can query it at any time "how many objects have you created?" ”。Package JXL;Class sum{public static int a=0;int C1;public sum

20161020 Problem Resolution Please click on the "Java Daily topic" 20161021 "below today's question. PackageOct2016; Public classQues1021 { Public Static voidMain (string[] args) {Ques1021 ques1021=NewQues1021 (); QUES1021.METHOD01 ("Test", 0);

Class Mytestclass {public int Value;public boolean equals (Mytestclass obj) {return obj. Value ==this. Value;}Public mytestclass (int initvalue) {Value = InitValue;}}This is the constructor of the class, or the constructor, which is called

From:http://outofmemory.cn/c/java-outofmemoryerrorJava.lang.OutOfMemoryError This error I believe most developers have encountered, the cause of this error is mostly due to the following reasons: The JVM memory is too small, the program is not tight,

Original address: http://blog.csdn.net/xiaanming/article/details/17483273Previously did not understand what called the callback, every day listen to people say add a callback method What, my heart think I grass, what is called callback method ah?

Thinking question 1In the early days we often defined variables like thisint value=100;The preceding example defines the variableMyclass.obj=new MyClass ();Are the variables defined in these two ways the same?Not the same. The former defines the

Java concurrency tool class ForkJoin task decomposition, tool class forkjoinIntroduction to the Fork/Join framework Step 1: Split the task. First, we need a fork class to split large tasks into subtasks. It is possible that the subtasks are still

Java concurrency deadlock instance, java dead instance 1 package com.thread.test.thread; 2 3 /** 4 * Created by windwant on 2016/6/3. 5 */ 6 public class MyTestDeadLock { 7 public void run() { 8 MyThread mt = new MyThread(); 9

HashMap specifies the initial capacity. For JDK computing of different versions, hashmapjdk The constructor of the specified initial capacity of HashMap: public HashMap(int initialCapacity, float loadFactor) The initial capacity is based on the

Difference between Vector and ArrayList in Java, vectorarraylist First, we can see that both of these classes implement the List interface, and the List interface has three implementation classes: ArrayList, Vector, and sorted List. List is used to

Java heap, Java Features: The memory area shared by the thread created when the VM is started. The memory area is allocated to all instance objects and array objects. Main area of GC spam Mobile Phone Manager management, GC heap The

For how to upload files under the Struts2 framework, the struts2 framework Struts2 configuration process (1) Add a jar package to the Project   (2) filter configuration in web. xml   struts2

Java object creation process, java object Creation 1. jvm finds the class file path. 2. The jvm loads the class file, performs static initialization, and creates a class object. 3. allocate memory space for the objects to be created. 4. clears

[Java daily question] 20161021, java20161021 20161020 for problem resolution, click "Java daily question" 20161021 below today's question to view Package Oct2016; public class Ques1021 {public static void main (String [] args) {Ques1021 ques1021 =

CountDownLatch multi-function synchronization tool, countdownlatch 1 package com. thread. test. thread; 2 3 import java. util. random; 4 import java. util. concurrent. *; 5 6/** 7 * CountDownLatch 8 * the synchronization policy allows one or more

Conversion between List and Json, and between ListJson List and Json conversion require six jar packages. If you do not reference these jar packages, you need to write a large amount of code, here, the conversion using the jar package is recorded