java - 搜索具有多种数据类型的 ArrayList

Question

我有一个 ArrayList String，int其中double包含 20 个元素。

我试图将 移至Strings字符串数组、ints移至 int 数组和doubles移至双数组。但我不知道如何，这就是我寻找整数的方法：

    private ArrayList <Object> randomList = new ArrayList <Object>();
    private int [] intArray = new int[10];

    public void example(){
    createArray();
    for(int i = 0; i<randomList.size();i++){
        if(randomList.get(i)instanceof Integer){
            intArray[i]= (Integer) randomList.get(i);
        }
    }
}

我不明白为什么这个 dosnt 起作用，它试图将不是整数的对象添加到我的数组中，导致 outOfBounds 异常，因为它试图添加超过 10 个元素。

Answer 1

您有索引不匹配，仅此而已。尝试类似：

int index = 0;

for(int i = 0; i<randomList.size();i++)
{
        if(randomList.get(i)instanceof Integer)
        {
            intArray[index++]= (Integer) randomList.get(i);
        }
}

您还应该检查特定数组的当前索引是否小于上限，即该数组的初始大小：

if(randomList.get(i) instanceof Integer && index < intArray.length)

Answer 2

您需要为每个输出数组维护一个单独的索引。

Answer 3

Well first of all you should never have allowed all these data types to congregate in on ArrayList of objects. But if you already have them:

for(Object o : randomList)
{
    if(o instanceof Integer)
    {
        //add to inteeger list
    }
    else if(o intenaceof String)
    {
       //add to string list
    }
    //...etc
}

Answer 4

1. Try initializing your array as :

   private int [] intArray = new int[randomList.size()];
   

2. Try another index to assign values to array:

   int count=0;
   for(int i = 0; i<randomList.size();i++){
       if(randomList.get(i)instanceof Integer){
          intArray[count++] = (Integer) randomList.get(i);
       }
   }        
   

3. In the end, you may want to truncate the array fragment which was unused using System.arraycopy as below:

   private int [] finalArray= new int[count;
   System.arraycopy(intArray, 0, finalArray, 0, count);
   

Answer 5

private int [] intArray = new int[10];

Your array has a size of 10, but your list does not have a size limit.

private int [] intArray = new int[randomList.size()];

might work.