core java for impatient

child class is placed in the parent class object, and only methods of the parent class can be called. 1 Employee empl = new Manager () 2 Empl.setbonus (100); // compile error, no Setbonus method in parent class 3 4 // You can convert a parent class reference to a subclass reference 5 if (empl instanceof Manager) { Span style= "color: #008080;" >6 Manager Mgr = (manager) Empl; 7 Mgr.setbonus (100 8 } When a method is declared final, the subclass cannot overwrite it. Final does

Java core programming-IO stream Overview (-), javaio 1. Four most critical parent classes of java io streams ~ InputStream (input byte stream) ~ OutputStream (output byte stream) ~ Reader (input stream) ~ Writer (output streams) All the above four classes are public abstract class classes. InputStream and OutputStream are transmitted in byte (byte. Reader

Basic data typesJava is the language of a strong data classThere are 8 basic data types, including:Integer 4 types Int (4 bytes) short (2 bytes) long (8 bytes) byte (1 bytes)The range and machine-independent lengths of integers in Java are certain, and do not cause integer overflow across platformsFloat type two double floatThe length of the double is twice times the length of the float, the double value but the part is used double, at the time of pre

pointer exception when the value is unboxing if the key does not exist get returns nullint count = Counts.getordefault ("A", 0);//Recommended UseThe counter, when present, adds one:Counts.merge (Word, 1, integer::sum);If the word key does not exist before, connect Word with 1, or use the Integer::sum function to add 1 to the previous valueP243 Map Method! I didn't read it.1 // Iteration Map 2 for (map.entry entry:counts.entrySet ()) {3 String k = entry.getkey (); 4 Integer V = entry.getval

The theoretical knowledge is boring, but these are basic skills and may be forgotten after learning. However, when used, we will find that the previous learning is very meaningful, and the learning thread is like this. 1. how to Create a lock? Lock lock = new ReentrantLock (); 2. How to Use the Lock? See the Lock document. The format is as follows: class X {private final ReentrantLock lock = new ReentrantLock ();//... public void m () {lock. lock (); // block until condition holds try {//... met

In Java, every variable, constant is a type.variables :Example: int i;Double A;1 The variable name must be a sequence of alphanumeric characters beginning with a letter. But unlike most programming languages, the range of letters and numbers in Java is larger, and the letters include ' a ' ~ ' Z ', ' a ' ~ ' Z ', ' _ ' or any Unicode character that represents a letter in any language, such as Chinese: decla

. String---> Byte streamCombines the functions of both bufferedwriter/outputstreamwriter2. can automatically refreshNew PrintWriter (os,true);UDP User Data Message Protocol-------------------------------------------1) Consider the efficiency of data transmission, reliability is not guaranteed2) Not necessarily a one-to-many communication, such as broadcasting3) non-connected, unreliable transmission modeDatagramsocket responsible for sending and receiving data such as the PostmanDatagrampacket d

Source of information: Software talent net Author: bristling super2002 I wrote an article on the Java implementation of the mail sent, when I wrote the message to send the function is very simple, can not bring attachments, can not have template. Later, a lot of friends asked me, there is no more perfect version, the existing mail sent me to write the design idea is convenient to send the attachment, you can send HTML pages including built-in pictures

;} Public String GetPassword () {return password;} public void SetPassword (String password) {this.password = password;} Public String Login () {string-sql = "SELECT * from Tb_user where t_username= '" + getusername () + "' and T_userpassword = '" +g Etpassword () + "'"; ResultSet RS = dao.executequery (sql), try {if (Rs.next ()) {return ' Loginin ';} return "Loginout";} catch (SQLException e) {//TODO auto-generated catch Blocke.printstacktrace (); return "Loginout";}} Public String Regist () {s

throws interrupterexception{ Sleep (delay);}10.synchronized keywords Public synchronized Voi Method () { method body}Equivalent to Public void method () { this. Intrinsiclock.lock (); Try { method body }finally{ this. Intrinsiclock.unlock ( ); }}11. Use Object Lock public class bank{ public void transfer (int from, int to, int mount) { synchronized -=amount; Accounts[to] +=amount; } System.out.println (...); private double [] Account; p

; } Private Statictarget) {T ret= (T) proxy.newproxyinstance (qrpcfactory.class. getClassLoader (),NewClass[] {target, irpccontext.class},NewInvocationhandler () {Qmodel Modelanno= Target.getannotation (Qmodel.class); Private ShortModel =Modelanno.value (); PrivateRpccontext CTX; @Override PublicObject Invoke (Object proxy, Method method, object[] args)throwsThrowable {if(Method.getname (). Equals ("SetContext")) { This. CTX = (rpccontext) args[0]; System.out.println ("SetContext

It can be mixed, without conflict. Ehcacheall the Cache interfaces are implemented. Ehcache . Each cache has a name and attributes, and contains Element. Ehcache in the Cache equivalent to a piece of cache area in another cache system. ElementElement is stored in Cache the atomic units in the. It has a key, a value , and a record of access. Element is either placed in the cache or removed from the cache . They may also be removed due to expiration, which relies on configuration. References:Sou

The core of the future model is the removal of the wait time for the main function and the time period that would otherwise have to wait for processing other business logic (according to Java Program Performance optimization).The future mode is somewhat similar to a commodity order. When you shop online, after you submit your order, you don't have to wait at home at the time of receipt to do something else.

This paper briefly introduces the core application of JCE framework. Javax.crypto.Cipher This class provides password functionality for encryption and decryption. It forms the core of the Java cryptographic Extension (JCE) framework. To create the Cipher object, the application invokes the Cipher getInstance method and passes the name of the requested transformat

when serializing.5) class used for serialization of objects: ObjectOutputStreamWriteObject (Object obj): ① serializes the given object. ② then writes.6) The class used by the deserialization of the object: ObjectInputStreamObject ReadObject (): Restores the read sequence of bytes to an object Case Study:650) this.width=650; "title=" Clipboard-28.png "src=" http://s3.51cto.com/wyfs02/M02/71/1C/ Wkiom1xfz9tyhdsfaanxrtvuejw190.jpg "alt=" Wkiom1xfz9tyhdsfaanxrtvuejw190.jpg "/>650) this.width=

List 13.1 Linklist/linkedlisttest.javaLinklist of Java ContainersPackage Linklist;import Java.util.linkedlist;import Java.util.list;import Java.util.listiterator;public class Linklisttest{public static void Main (String args[]) {list Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced. Java Core Technology Vo

routine to review the concepts that we have described earlierPackage pair3; Public classpairtest3{ Public Static void Main(string[] args) {Manager CEO =NewManager ("Gus greedy.",800000,2003, A, the); Manager CFO =NewManager ("Sid Sneaky",600000,2003, A, the); PairNewPair1000000); Cfo.setbonus (500000); Manager[] Managers = {CEO, CFO}; pairNewPair out. println ("First:"+ Result.getfirst (). GetName () +", Second:"+ Result.getsecond (). GetName ()); Maxminbonus (managers, result); Syste

Next how to ImplementFirst step: First, the service class, call method to convert to digital, easy to transferThe second step: Extract meta-information, extraction and three ways, three kinds have advantages, the best way is the first1. Processing when compiling Java2. Program start-up processing, preprocessing3. Call processing, lazy processingStep Three: Encoding interpretationFourth Step: Request methodFifth Step: Distributed supportThe first step:@Target (Elementtype.type) @Retention (retent

=str.tostring ();8 System.out.println ("After insertion:" +STR2);Output Result: 12Hello world!After insertion: Hello world!!Note : StringBuffer and StringBuilder function the same, but StringBuffer is thread-safe, and StringBuilder does not implement thread-safe functionality, so performance is slightly higher. Therefore, in general, if you need to create a variable-content string object, you should consider using the StringBuilder class as a priority.Second,"= =" and equals () What is the diffe

constructor with reflection----> Create ObjectPackage classinstance;//uses reflection to call the constructor--Create object import java.lang.reflect.constructor;class Peson {public Peson () { System.out.println ("parameterless constructor");} Public Peson (String name) {System.out.println ("parameterized constructor" + name);} Private Peson (String name, int age) {System.out.println ("parameterized constructor" + name + "," + Age);}} public class Cteateobject {public static void main (string[]