小编Min*_*ine的帖子

我一直在阅读关于"Java Transaction"的内容,我对它的含义感到困惑？什么是有用的？

概述:这是我的第一个Websphere 7 Server&JPA 1.0&EJB&Derby Database的教程.

第一:我的数据源名称是EJB3BANK,我的目标数据库是SHOP.

第二:这是persistence.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0"
xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
<persistence-unit name="ShopJPA" transaction-type="JTA">
    <jta-data-source>jdbc/EJB3BANK</jta-data-source>
    <non-jta-data-source>jdbc/EJB3BANK</non-jta-data-source>
    <properties>
        <property name="openjpa.jdbc.Schema" value="SHOP" />
    </properties>
</persistence-unit>
</persistence> 

第三:Item实体Class的部分代码

@Entity
@Table(schema = "SHOP", name = "ITEM")
@NamedQuery(name = "getItem", query = "SELECT i FROM Item i")
public class Item{...}

第四:这里是业务类CartBean,这里是问题的开始

@Stateful
CartBean implements Cart{
....
....
public List<Item> getItems() {      
javax.persistence.Query query = em.createNamedQuery("getItem");//the problem here
return query.getResultList();
}
}

这是错误消息:必须在ConnectionDriverName属性中指定JDBC驱动程序或DataSource类名.如何解决这个问题？

List listOne = new LinkedList<Shxx>();      
List<Shxx> listTwo = new LinkedList<Shxx>();
List listThree = new LinkedList();
List<Shxx> listFour = new LinkedList();

我一直在研究 Java EE 6，我对注释和约束之间的区别感到困惑。它们之间到底有什么区别呢？

我的情况是将一个字符串分成字符串数组,然后将每三个字符转换为一个字符串.(例如"xxxyyy" - > ['xxx','yyy'])

const translate = function (RNA) {
    var arrRna = Array.from(RNA);
    var arr = [];
    for (var key in arrRna) {
        if ((key % 3) == 0) {
            var temp = RNA.slice( key,  (key+3));
            arr.push(temp);
        }

    }
    return arr;
}

console.log(translate('xxxyyyzzz'));

预期结果 : ['xxx','yyy','zzz']

但我想要的结果是: [ 'xxx', 'yyyzzz', 'zzz' ]

此外,我注意到切片方法在第一次迭代中按预期工作,但在此之后,奇怪的结果 - >'yyyzzz'.为什么？？

// The problem in Starter() 
// with any line before x = 5 ; for example System.out.println(" Anything");
// the result "x = 4" 

// but without the result = "x = 9"
// Why??????


    public class Starter extends Thread {

    private int x = 2;

    public static void main(String[] args)
    throws Exception{


        new Starter().wakeItSo();
    }

    Starter() {

        // Next line (with or without it)
        System.out.println("anything");    


        x = 5;
        start();

    }

    public void wakeItSo()
    throws Exception{

        //join();


        x = x …

package pkg_2;

import java.util.*;

class shape{}

class Rect extends shape{}

class circle extends shape{}

class ShadeRect extends Rect{}

public class OnTheRun {

    public static void main(String[] args) throws Throwable {
        ShadeRect sr = new ShadeRect();
        List<? extends shape> list = new LinkedList<ShadeRect>();       
        list.add(0,sr);
    }

}

package pkg_1;

public class ExpOnWaitMethod extends Thread {

    static Double x = new Double(20);


    public static void main(String[] args) {

        ExpOnWaitMethod T1 = new ExpOnWaitMethod();
        ExpOnWaitMethod T2 = new ExpOnWaitMethod();

        T1.start();

        T2.start();

    }

    public void run() {

        Mag mag = new Mag();

        synchronized (x) {

            try {
                for (int i = 1; i < 10; i++) {
                    mag.nop(Thread.currentThread());
                    x = i * 2.0;

                }

            } catch (InterruptedException e) {

                e.printStackTrace();
            }

        }
    }

}

class Mag {
    char ccc = …

2个问题:

1. str字段在A类型的两个实例之间共享[第2行]
2. 根据以下代码有什么影响？

class A implements Runnable {
    String str = "hello"; // line 2.

    public void run(){
        Synchronized(str){
            System.out.println(str+" "+Thread.currentThread().getName());
            Thread.sleep(100);
            System.out.println(str+" "+Thread.currentThread().getName());
            //anything
        }
    }

    public void static main(String[] args){  
        Thread one = new Thread(new A(),"one").start();  
        Thread two = new Thread(new A(),"two").start();  
    }
}