Question

我目前正在尝试将现有的Processing项目集成到Eclipse中。有两个类，TagCloud和Tag，前者是后者的控制器。在TagCloud中，我有以下代码片段：

for (int i = 0; i < NUM_RELATIONS; i++) {
          println("i: " + i);
          tags.get(i).refTagsMap(tagsMap);
          tags.get(i).setLinks();
          //Randomly assign a location to  the first tag.
          System.out.println("Tag from map: " + tags.get(i));
          for(int j = 0; j < tags.size(); j++)
              System.out.println(j + " " + tags.get(j));
          tags.get(i).drawTag();
        }

        for(int i = 0; i < NUM_RELATIONS; i++) {
          println("Drawing tags for tag: " + i); 
          tags.get(i).drawLinks();
        }

tags是Tag对象的ArrayList，tagsMap是HashMap（String，Tag）类型的HashMap。但是，代码在tags.get(i).drawTag()方法中断，并显示以下异常。

Exception in thread "main" java.lang.RuntimeException: java.lang.NullPointerException
    at processing.core.PApplet.runSketch(PApplet.java:10713)
    at processing.core.PApplet.main(PApplet.java:10525)
    at TagCloud.main(TagCloud.java:97)
Caused by: java.lang.NullPointerException
    at processing.core.PApplet.noFill(PApplet.java:14574)
    at Tag.drawTag(Tag.java:65)
    at TagCloud.<init>(TagCloud.java:87)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
    at java.lang.Class.newInstance(Class.java:438)
    at processing.core.PApplet.runSketch(PApplet.java:10711)
    ... 2 more

以下是drawTag()和drawLink方法

public void drawTag() {
  parent.noFill();
  parent.stroke(255);
  parent.strokeWeight(3);    
  float x = location.x;
  float y = location.y;
  //Create the rectangle frame
  frame = parent.createShape(parent.RECT, x, y, 100, 80);
  //Add it to the canvas
  parent.shape(frame);

  //Write the text
  parent.text(topic, x + 15, y + 25);
}


public void drawLinks() {
    System.out.println();
    parent.stroke(255);
    parent.strokeWeight(1);
    for(int i = 0; i < linkKeys.size(); i++)
    {
      Tag linkedTag = links.get(linkKeys.get(i));
      System.out.println(linkedTag);
      int x = (int)linkedTag.getLocation().x;
      int y = (int)linkedTag.getLocation().y;
      PShape line = parent.createShape(parent.LINE, location.x, location.y, x, y);
      //Add the shape to the 
      parent.shape(line);
      linkLines.add(line);
    }
  }
}

parent是在Tag的构造函数中传递的PApplet。

Answer 1

所以我发现了错误。在我的TagsCloud对象的构造函数中，我正在初始化Tag对象并尝试将一个ref传递给TagsCloud对象。但是，TagsCloud构造函数尚未完成执行，因此TagsCloud对象尚未完全初始化，因此NullPointerException

将Processing集成到Eclipse中时出现NullPointerException

1 个答案: