JavaFX 8如何在几乎空的Application类中启动JavaFX Application线程？ [英] How does JavaFX 8 start the JavaFX Application thread in a nearly empty Application class?

问题描述

让我们说，我们有以下类：

Lets say, we have the following class:

import javafx.application.Application;
import javafx.stage.Stage;

public class Test extends Application
{
    public Test()
    {
        System.out.println("Constructor");
    }

    @Override
    public void start(Stage primaryStage) throws Exception
    {
        System.out.println("start");
    }

    public static void main(String... args)
    {
        System.out.println("main");
    }
}

它来自应用但它不使用任何方法。通常你通过在main中调用 launch（args）来启动一个JavaFX应用程序。

It's derived from Application but it doesn't use any of its methods. Usually you start a JavaFX application by calling launch(args) in the main.

当我启动这个程序时只有输出是main，所以不调用构造函数和start，但程序不会因为运行JavaFX Application线程而终止。但是它来自哪里？

When I start this program the only output is "main", so the constructor and start aren't called, but the program doesn't terminate because there is a JavaFX Application thread running. But where does it come from?

我做了一些调试，发现线程是在main方法运行之前从主线程启动的。堆栈跟踪以 NativeMethodAccessorImpl 开始。

I did some debugging and found out that the thread is started from the main thread before the main method runs. The stack trace starts with NativeMethodAccessorImpl.

为了更加奇怪：当我从另一个类启动main方法时，JavaFX应用程序线程未启动：

To get even weirder: when I start the main method from a different class, the JavaFX Application thread isn't started:

public class Test2
{
    public static void main(String[] args)
    {
        Test.main(args);
    }
}

那么这是什么样的黑魔法？

So what kind of black magic is this?

推荐答案

Java使用不同的方法启动这两个应用程序。

Java uses different approaches to launch the two applications.

尝试运行以下代码：

public class Test3 {

    public static void main(String[] args) {

        Class<?> actualMainClassTest = LauncherHelper.checkAndLoadMain(true, 1, Test.class.getName());
        Class<?> actualMainClassTest2 = LauncherHelper.checkAndLoadMain(true, 1, Test2.class.getName());

        System.out.println("Actual loaded main class for Test: " + actualMainClassTest.getName());
        System.out.println("Actual loaded main class for Test2: " + actualMainClassTest2.getName());
    }
}

输出

• Test的实际加载主类：sun.launcher.LauncherHelper $ FXHelper


• Test2的实际加载主类：Test2

您可以看到 Test2 类的实际加载主类是 Test2 ，但加载的主要类
测试是 sun.launcher.LauncherHelper $ FXHelper 。

You can see that the actual loaded main class for the Test2 class is Test2, but the loaded main class for Test is sun.launcher.LauncherHelper$FXHelper.

这是因为Java启动程序检查要启动的主类是否是 javafx.application的子类。应用。
如果是，它会加载 sun.launcher.LauncherHelper $ FXHelper 的主方法，它会调用JavaFX应用程序的启动程序方法
（ com.sun.javafx.application.LauncherImpl＃launchApplication ）。

This happens because the Java launcher checks if the main class to be launched is a subclass of javafx.application.Application. If it is, it loads the main method of sun.launcher.LauncherHelper$FXHelper instead, which invokes a launcher method for JavaFX applications (com.sun.javafx.application.LauncherImpl#launchApplication).

此方法负责启动JavaFX应用程序。 在启动应用程序后调用＃main ：

This method is responsible for launching the JavaFX application. Test#main is called after the application is launched:

当测试#main 由Test2调用，不使用FX启动器，因为Test2不是 javafx.application.Application 的子类。

When Test#main is called by Test2, the FX launcher is not used because Test2 is not a subclass of javafx.application.Application.

这篇关于JavaFX 8如何在几乎空的Application类中启动JavaFX Application线程？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！