我知道这里有很多关于 Java 中 NoSuchElementException 的线程,但我仍然无法弄清楚这里发生了什么
我正在尝试为传递依赖项 Kata 18 提出一个解决方案,该解决方案发布在http://codekata.pragprog.com/2007/01/kata_eighteen_t.html
dependencies_for 方法应该接受一个 char 项目并计算该项目的所有依赖项。当我尝试将元素添加到 finalDependencies ArrayList 时发生异常
这是我的 NullPointerException 发生的地方。我已经跟踪了所有这些数据结构,它们都没有 Null 值。我不明白是什么导致了我的异常。请看我的代码:
public class Test_Dependencies
{
public static void main(String[] args) {
Dependencies Dep = new Dependencies();
Dep.add_direct('A', "B C");
Dep.add_direct('B', "C D");
Dep.dependencies_for('A');
}
}
public class Dependencies {
HashMap dependenciesList;
public Dependencies()
{
HashMap<Character, ArrayList> dependenciesList = new HashMap<Character, ArrayList>();
}
public void add_direct(char mainItem, String dependentItems)
{
// code that works here
}
public String dependencies_for(char item)
{
ArrayList finalDependencies = new ArrayList<Character>();
Character key = new Character(item);
//get initial dependencies for the item and add them
ArrayList processingDependencies = dependenciesList.get(key);
Iterator itr = processingDependencies.iterator();
while(itr.hasNext())
{
if(finalDependencies.contains(itr.next()) == false && itr.next() != key)
{
// NoSuchElement exception here
finalDependencies.add(itr.next());
// look again at each item in dependenciesList. If it is in the list then add it to processingDependencies
if(dependenciesList.containsKey(itr.next()) && !processingDependencies.contains(itr.next()))
{
processingDependencies.add(itr.next());
}
}
}
// turn finalDependencies into a string
itr = finalDependencies.iterator();
String allDependencies = "";
while(itr.hasNext())
{
allDependencies = allDependencies + " " + itr.next();
}
return allDependencies;
}
}
我有点困惑,因为 processingDependencies 和 finalDependencies ArrayLists 不为空。并且 processingDependencies arraylist 包含一个项目