j2se

1. Configure persistence. xml 2. In the j2se environment, only the entitymanager managed by the application can be used and transactions can be manually controlled. Public class testclient {public static void main (string [] ARGs) {entitymanagerfactory EMF = persistence. createentitymanagerfactory ("bookstorepu"); entitymanager em = EMF. createentitymanager (); try {// start em of the transaction. gettransaction (). begin ();/* entity operation * //

Use j2se API to read properties files 1. Use the load () method of Java. util. properties classExample: inputstream in = lnew bufferedinputstream (New fileinputstream (name ));Properties P = new properties ();P. Load (in ); 2. Use the getbundle () method of the Java. util. resourcebundle classExample: resourcebundle RB = resourcebundle. getbundle (name, locale. getdefault ()); 3. Use the constructor of the Java. util. propertyresourcebundle classExamp

();} Synchronized (CHOPSTICKS1) {System.out.println ("Maria successfully grabs two chopsticks, she's going to eat!") ");}}}}}in the example, Danny and Maria grab each chopsticks when the chopsticks will be held in hand, when Danny grabbed chopsticks 1,maria grab chopsticks 2 o'clock, they are waiting for each other to give up chopsticks, do not give, infinite wait, this happened to deadlock. Therefore, use the lock to be cautious, when it comes to synchronization, it is important to consider wh

J2SE Knowledge Points Induction Note (vii)---Java IO Part 2: Get keyboard input and IO Flow system diagram--Reprint Please specify Source: Coder-pigIntroduction to this section:Well, in the previous section we have introduced the use of file and Randomaccessfile classes, and this section we will talk about someCommonly used things, if you learn C + + or C's friends know, get keyboard input is very simple, scanf () and CIN canGet the parameters we've e

string ("World"); String A4=new string ("World"); System.out.println (A1==A2); Output is trueSystem.out.println (A3==A4); Output to False}}To compare reference types with equalsThe Equals method is defined in the base class object, and this method compares the memory address of the object, that is, if the "P1==P2" is replaced with P1.equals (P2) in the previous example, the result is the same.Special circumstances, If a class does not have its own definition of the Equals method, its defa

J2se|window An example uses the j2se5.0 Processbuilder class to perform an external program, which is more convenient than the runtime.exec and can set environment variables. Package Com.kuaff.jdk5package;import Java.io.ioexception;import Java.io.inputstream;import java.util.ArrayList; Import Java.util.list;public class processbuildershow{public static list

J2se| Loop | statement A statement like this before: void Cancelall (Collection c) { for (Iterator i = C.iterator (); I.hasnext ();) { TimerTask TT = (timertask) i.next (); Tt.cancel (); } } You can write this later: void Cancelall (Collection c) { for (Object o:c) ((TimerTask) O). Cancel (); } Sometimes we might write this code: List suits = ...; List ranks = ...; List Sorteddeck = new ArrayList (); for

When a parent class implements the Serializable interface, its sub-classes are automatically serialized.This is verified as follows:Package Serial;Import java. io. Serializable;Public class SuperC implements Serializable {// The parent class

Recently, I encountered a scenario in my graduation project: I need to dynamically package an existing project when running a web project. Because we have encountered similar situations in some projects before, I have positioned the solution to the

Creating a project is the same as creating a Java program. Import Java. AWT. graphics; import javax. swing. jframe; import javax. swing. jpanel; public class simpleswinghelloworld {/***** @ title: Main * @ description: program entry * @ Param ARGs

Benefits of generics JavaIntroducing generics in a language is a major enhancement in functionality. Not only have the language, type system, and compiler greatly changed to support generics, but also the class libraries have been greatly revised.

After reading the I/O chapter, I feel like there are a lot of streams! Messy! There are many examples in this chapter, and the relationship is also very messy. After I have learned this chapter, I basically don't know which stream is used. Next, I

Java embodies a simple programming style everywhere. serialization is one of the most commonly used functions. The design in Java is particularly "simple ". With the help of objectinputstream and objectoutputstream, we can easily implement

Equals MethodThe equals method of the object is defined as: X. equals (y) compares the addresses of two objects in the heap memory, which is equivalent to X = Y. Therefore, false is returned unless X and Y point to the same object;If you want to use

Jdk5.0 advanced SynchronizationSemaphore class (semaphore)That is, you can allocate a license to the thread and specify the number of licenses to synchronize multiple threads.Semaphore S = new semaphore (4); // four licenses can be allocated. When

Java Process ControlControl FlowIf ()If ().... ElseIf ()..... Else if ().... ElseNote: else is only paired with the nearest if () on the same layer above it. switch(){case 'a':……..case 1:……break；default:…………} Note:The data type in switch () is byte

Random File AccessRondomaccessfileClass allows random access to files. This class also supports direct output of various data types.Getfilepoint() To know the pointer position in the file, useSeek() Positioning.Mode ("R": random read; "W": Random

Anything is object (all objects)Abstract: extract useful information from a specific object.An object has its inherent attributes. Its method is the behavior of an object (What can an object do)Objects are simple (simple functions). Multiple objects

Java multi-thread programmingHere we need to recall the process, that is, the running program, a concurrent task in the multitasking operating system (The CPU runs multiple processes on time slice.), Thread. Its essence is the sequential execution

Concurrent processing of shared data Resources that are concurrently accessed by multiple threads are called critical resources.Multiple ThreadsSimultaneously accessing objectsIt is required that an atomic operation be split when the same resource