java - 难以理解嵌入在数据类结构中的对象数组

Question

我正在尝试创建一个静态的嵌套数据结构。嵌套项之一是对象数组。我似乎无法将新对象分配给该数组。对于以太坊中的广大大师来说，这很可能是微不足道的。

/////////////////////////////////////////////////////
class test
/////////////////////////////////////////////////////
{

 //===========================================
 public static class DataClass
 //===========================================
  { 
    static String thing = new String("thing 1");
  
    public static class InnerClass
    { 
      static String thing = new String("thing 2");
      
      public class this_thingy
      {
        String thing;
        String other;
        void init() { thing="thing 3"; other="other"; }
      } 
      public static this_thingy[] classArray = new this_thingy[3];
      
    }

  }//DataClass

 //===========================================
  public static void main( String[] args )
 //===========================================
  {
    System.out.println( DataClass.InnerClass.thing );
    
    System.out.println( DataClass.InnerClass.classArray[0].thing );
    System.out.println( DataClass.InnerClass.classArray[0].other );
  }//main

}//test


/*
null
Exception in thread "main" java.lang.NullPointerException: Cannot load from object array because "test$DataClass$InnerClass_3.InnerClass_3a" is null
        at test.main(test.java:31)
*/

Answer 1

您需要初始化数组的每个元素。

public static class this_thingy{
    String thing;
    String other;
    void init() { thing="thing 3"; other="other"; }
} 
public static this_thingy[] classArray = new this_thingy[3];
static {
   for(int i = 0; i < classArray.length; i++){
      (classArray[i] = new this_thingy()).init();
   }
}