pdf417 scanner javascript Recipe in Java

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then it works and gives us a value of around 10 50 milliseconds, the difference between the script first executing and the page loading up. Although we have declared createTime as being local to the constructor function scope, it cannot be garbage-collected so long as Robbie the robot is still referenced, because it has been bound up in a closure. The closure works only if the inner function is created inside the outer one. If we refactor my code to predefine the getAge function and share it between all robot instances, like so

We do not add this to the SCM system, and we alter its file permissions to be readable only by the owner. We now want a target to load the named file into a set of properties and deploy to the named server. We do this through the <property file> technique, this time to a <param> element inside the <antcall>:

<map name="images" lazy="true" table="ITEM_IMAGE"> <key column="ITEM_ID"/> <index column="IMAGE_NAME" type="string"/> <element type="string" column="FILENAME" not-null="true"/> </map>

Figure E.3 The Select Installation Directory screen. Unless there is a reason not to do so, accept the defaults here.

There is a fundamental difference in the way you access data in Java and in a relational database. In Java, when you access a user s billing information, you call aUser.getBillingDetails().getAccountNumber() or something similar. This is the most natural way to access object-oriented data, and it s often described as walking the object network. You navigate from one object to another, following pointers between instances. Unfortunately, this isn t an efficient way to retrieve data from an SQL database. The single most important thing you can do to improve the performance of data access code is to minimize the number of requests to the database. The most obvious way to do this is to minimize the number of SQL queries. (Of course, there are other more sophisticated ways that follow as a second step.) Therefore, efficient access to relational data with SQL usually requires joins between the tables of interest. The number of tables included in the join when retrieving data determines the depth of the object network you can navigate in memory. For example, if you need to retrieve a User and aren t interested in the user s billing information, you can write this simple query:

You define a lambda expression using this syntax:

OK, take a breath. That was a lot of code to go through. But if you run the program now, you won t see any difference at all. We still need to connect all of the record editors to the main form. They all connect through the LinkLabel controls on the main form s Administration panel (PanelAdmin). We need to add 12 LinkClicked event handlers to access all of the new and various forms. Go ahead and add them now to the MainForm class.

So does this one:

Different systems group concerns differently, so they define different layers. A typical, proven, high-level application architecture uses three layers: one each for presentation, business logic, and persistence, as shown in figure 1.4. Let s take a closer look at the layers and elements in the diagram:

server to respond and update the UI with the response obtained. Bingo! You just encountered Swing s single-thread rule problem. You are not supposed to update any UI component in a nonevent-dispatching thread. If the thread waiting for the server to respond updates the component while the AWT thread is repainting the UI component, it may result in UI anomalies or even worse a crash. The same kind of problem would occur if you used a callback mechanism using RMI. In that case, the callbacks would be invoked in RMI threads, and updating the state of Swing components from the thread would lead to a violation of the threadsafety rule. As with most multithreading-related problems, these problems are hard to reproduce and therefore hard to fix. Murphy s law seems to work well with the single-thread rule: If you violate the single-thread rule, the problems always seem to occur during the customer demo of your product! 9.1.3 The solution To ensure safe access from a nonevent-dispatching thread, Swing allows a thread to request that the event-dispatching thread carry out the operation on its behalf. With this mechanism, the caller thread makes the request, while the eventdispatching thread carries out the actual operation when processing the request. By requiring that the component s state be accessed and manipulated only from a preassigned thread, and by providing a mechanism for passing the request to the preassigned thread, Swing removes the burden of dealing with thread-safety issues from the Swing component s developers. Threads can pass requests to perform operations to an event-dispatching thread through the use of EventQueue.invokeLater() or EventQueue.invokeAndWait(). (You will see the difference between both shortly.) With either, you pass a Runnable object, and the run() method within it performs the intended operation. Such a solution requires writing a class extending Runnable for each method that needs to be called from a nonAWT thread and using those classes instead of direct calls. This has two problems:

return System.getProperty(sysPropName);