java – 未处理的异常类型：processing.org中的InstantiationException

2019年8月6日 173次阅读

我正在尝试从处理中做一个简单的Class.newInstance(),但我失败了:(

EDIT: as below instructed, the reason it didn’t work was that Processing wraps all
code into a class making all declared classes internal classes. The java
language specification states that newInstance() for internal classes
should be passed a reference to the container class, so after changing
the call to newInstance to newInstance(this); it worked as intended.

下面抛出InstantiationException的代码示例.

Docs说有一个公共构造函数,一切都会好的,但唉.

运行处理2.2.1

代码流：它填充了实现接口的所有类的列表.然后我们通过state.runnableTypes并尝试(但失败)实例化该类型的新实例.

请帮忙？

(对于笨重的状态变量道歉,与偶数笨重的ryo单元测试系统有关;))

    State state;
/* It nicely finds the Wtf class and inserts that into its classes array, 
 * but when i try to instantiate a new one, whatever I try, it throws :(
 */
void setup() {
  size(1024, 768, P3D);
  noLoop(); 
//get all the classes
  state = new State();
  Class[] types = this.getClass().getDeclaredClasses();
  state.allTypes = types;

  //enumerate castable types
  for (int i = 0, l = types.length; i<l; i++) { 
    Class c = types[i];
    if ( !c.isInterface() && IMenuRunnable.class.isAssignableFrom(c) ) { 
      println("adding "+c.toString());
      state.runnableTypes.put(c.getSimpleName(), c);
    }
  }

  //loop through the list and create some instances //FIXME: Exception handling ;p
  for ( String s : state.runnableTypes.keySet () ) { 
    Class c = state.runnableTypes.get(s);
    IMenuRunnable u = (IMenuRunnable) c.newInstance(); // ERR: calling Class.newInstance() here throws an error??
    java.lang.reflect.Constructor[] ctors = c.getConstructors();
    for ( java.lang.reflect.Constructor ctor : ctors ) { 
      ctor.setAccessible(true);
      Object o = ctor.newInstance(); // ERR: going via constructor array, same error :(
    }
  }
}




void draw() { 
  background(0);
}




class State {
  Class[] allTypes;
  HashMap<String, Class> runnableTypes = new HashMap<String, Class>();
}



interface IMenuRunnable {
}



public class Wtf implements IMenuRunnable { 
  public Wtf() {
  }
}

最佳答案 首先,您的代码无法编译,因为您需要在try / catch块中包装newInstance(). newInstance()函数可以抛出InstantiationException或IllegalAccessException,因此您必须捕获这些异常.这就是你的错误告诉你的.

如果你发布一个MCVE,你会有更好的运气,比如这个：

void setup() {
  try {
    Class<Wtf> c = Wtf.class;
    IMenuRunnable u = (IMenuRunnable) c.newInstance();
    println(u.toString());
  }
  catch(Exception e) {
    e.printStackTrace();
  }
}

interface IMenuRunnable {}

public class Wtf implements IMenuRunnable{ 
  public Wtf() {
  }
}

但即使你修复了它,你也会得到一个运行时异常,因为在幕后,你在草图中声明的类是sketch类的内部类.你不能像你想要的那样在内部类上使用反射.

因此,您需要更改声明这些类的方式,或者需要更改您进行反射的方式.

要确保Processing不会将这些类转换为草图的内部类,您必须在它们自己的.java选项卡中定义它们.使用类的名称后跟.java,因此Processing知道它是一个Java类,而不是“Processing class”,它被转换为内部类.您的设置如下所示：

使用这种方法,您必须将草图的实例传递给java类,以便访问任何Processing方法.相反,您可能只想改变您的反思方式.由于类是sketch类的内部类,因此必须通过sketch类来获取它们：

void setup() {
  try {

    Class<?> sketchClass = Class.forName("sketch_150702a");
    Class<?> innerClass = Class.forName("sketch_150702a$Wtf");

    java.lang.reflect.Constructor constructor = innerClass.getDeclaredConstructor(sketchClass);

    IMenuRunnable u = (IMenuRunnable)constructor.newInstance(this);
    println(u.toString());
  }
  catch(Exception e) {
    e.printStackTrace();
  }
}

interface IMenuRunnable {
}

public class Wtf implements IMenuRunnable { 
  public Wtf() {
  }
}

或者,您可以将Wtf类声明为static：

void setup() {
  try {
    Class<Wtf> c = Wtf.class;
    IMenuRunnable u = (IMenuRunnable) c.newInstance();
    println(u.toString());
  }
  catch(Exception e) {
    e.printStackTrace();
  }
}

interface IMenuRunnable {}

static public class Wtf implements IMenuRunnable{ 
  public Wtf() {
  }
}

当然,那么您将无法访问草图类的非静态成员,因此您采用哪种方法实际上取决于您需要做什么.

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