Java中main函数的执行过程以及在程序中开启断言

%JAVA_HOME%/lib 中存在 tools.jar，无意中发现其中的 javac的代码实现如下：

package com.sun.tools.javac;

import com.sun.tools.javac.util.Version;
import java.io.PrintWriter;
import java.lang.reflect.Method;

@Version("@(#)Main.java\t1.25 06/04/30")
public class Main
{
  public static void main(String[] paramArrayOfString)
    throws Exception
  {
    if ((paramArrayOfString.length > 0) && (paramArrayOfString[0].equals("-Xjdb"))) {
      String[] arrayOfString = new String[paramArrayOfString.length + 2];
      Class localClass = Class.forName("com.sun.tools.example.debug.tty.TTY");
      Method localMethod = localClass.getDeclaredMethod("main", new Class[] { paramArrayOfString.getClass() });
      localMethod.setAccessible(true);
      System.arraycopy(paramArrayOfString, 1, arrayOfString, 3, paramArrayOfString.length - 1);
      arrayOfString[0] = "-connect";
      arrayOfString[1] = "com.sun.jdi.CommandLineLaunch:options=-esa -ea:com.sun.tools...";
      arrayOfString[2] = "com.sun.tools.javac.Main";
      localMethod.invoke(null, new Object[] { arrayOfString });
    } else {
      System.exit(compile(paramArrayOfString));
    }
  }

  public static int compile(String[] paramArrayOfString)
  {
    com.sun.tools.javac.main.Main localMain = new com.sun.tools.javac.main.Main("javac");

    return localMain.compile(paramArrayOfString);
  }

  public static int compile(String[] paramArrayOfString, PrintWriter paramPrintWriter)
  {
    com.sun.tools.javac.main.Main localMain = new com.sun.tools.javac.main.Main("javac", paramPrintWriter);

    return localMain.compile(paramArrayOfString);
  }

  static
  {
    ClassLoader localClassLoader = Main.class.getClassLoader();
    if (localClassLoader != null)
      localClassLoader.setPackageAssertionStatus("com.sun.tools.javac", true);
  }
}

其中通过获取当前类加载器的实例进行指定断言开启

ClassLoader localClassLoader = Main.class.getClassLoader();

if (localClassLoader != null)

localClassLoader.setPackageAssertionStatus("com.sun.tools.javac", true);

并且通过该类的main方法中调用另外一个可以作为入口类的main方法的过程，可以猜想jvm在启动的时候通过指定入口类其调用方式应该也是一致的

Class localClass = Class.forName("com.sun.tools.example.debug.tty.TTY");

Method localMethod = localClass.getDeclaredMethod("main", new Class[] { paramArrayOfString.getClass() });

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