Java 反射 : Code runs fine in Debugger but not in "normal" running mode

Question

我正在尝试从方法数组中调用静态方法。这在调试器中工作得很好，但在正常运行模式下却不行。这是为什么？

下面的代码注释中有更多描述..

为了更容易重现而编辑，只需在调试器与正常模式下运行此类:

public class Stackoverflowquestion {

public static class Backautomat {
    private String aktuellBackendeBrotsorte = "Butterbrot";
    //Test für Statische Methoden: Brauche ich dazu auch eine Instanz für Invoke? 
    public static String getBezeichnung(){
        return "Bezeichnung: Bester-Backautomat-Ever";
    }
    //Test für Methoden ohne Parameterliste
    public boolean backautomat_starten(){
        return true;
    }
}

public static void main(String[] args) throws IllegalAccessException, IllegalArgumentException, InvocationTargetException {
    //Get all methods of class
    Method[] backaudomadMethoden = Backautomat.class.getMethods();
    //Get first Method of class -> I know this one is static -> see in source "Backautomat"
    Method backMethod =  backaudomadMethoden[0];
    //Printing out Method Name: In Debugger this returns the static method name: getBezeichnung(),
    //In "normal" running mode (Run -> Run as -> Java Application) it prints out the second method: backautomat_starten()
    System.out.println(backMethod.getName());
    //Invocation is successfull in debugger
    //Invocation throws exception running in "normal" mode
    System.out.println(String.valueOf(backMethod.invoke(null)));

}

EDIT 异常如下所示:

backautomat_starten Exception in thread "main" java.lang.NullPointerException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.relfection.easy.example.Stackoverflowquestion.main(Stackoverflowquestion.java:31)

Answer 1

考虑 documentation of Class.getMethods() :

…

The elements in the returned array are not sorted and are not in any particular order.

这意味着当前 JRE 的任意方面都可能具有改变结果的副作用，包括在调试器中运行。

因此，如果数组中的第一个方法不是您期望的方法，那么当尝试像 static 方法一样运行实例方法时，获得与预期不同的名称并产生异常，是以下症状同样错误的假设。