Java将ArrayList <Integer>添加到ArrayList <ArrayList <Integer >>替换ArrayLists的ArrayList的所有元素

Question

我为长标题道歉,如果你能想到更好的标题,请告诉我!

我正在做的是尝试创建ArrayLists的ArrayList并逐个添加ArrayLists.AL<AL<I>>我拥有的两个被称为三角形和正方形,我AL<I>s通过addToList()方法添加 - 将被AL<I>调用的temp 添加到适当的AL<AL<I>>.temp似乎没有问题,但是在我运行整个方法figurateNumbers()之后,我AL<AL<I>>s只包含[98,70],这是要添加的最后一个临时值.代码如下:

import java.util.ArrayList;
import java.util.Iterator;

    public class problem
    {
        public static ArrayList<ArrayList<Integer>> triangle = new ArrayList<ArrayList<Integer>>();
        public static ArrayList<ArrayList<Integer>> square = new ArrayList<ArrayList<Integer>>();
        public static ArrayList<Integer> temp = new ArrayList<Integer>();

        public static void figurateNumbers() 
        //Inserts into individual arraylists, numbers, all figurate numbers square : octagonal
        {
            for (int ii = 1; ii < 141; ii++) 
            {
                if ((ii * ii >= 1000) & (ii * ii < 10000))
                    addToList(ii * ii , square);
                if (((ii * ii + ii) / 2 >= 1000) & ((ii * ii + ii) / 2 < 10000))
                    addToList((ii * ii + ii) / 2 , triangle);
            }
}


    public static void addToList(int num, ArrayList<ArrayList<Integer>> list)
    //Splits the two parts of the number and inserts the arraylist into the proper arraylist
    {
        temp.clear();
        int numInt_one = Integer.parseInt(String.valueOf(num).substring(0,2));  
        int numInt_two = Integer.parseInt(String.valueOf(num).substring(2,4));  
        temp.add(numInt_one);
        temp.add(numInt_two);
        list.add(temp);
    }

    public static void main (String [] args) 
    {
        figurateNumbers();

        System.out.println(triangle.size());
        System.out.println(square.size());
    Iterator<ArrayList<Integer>> it = square.iterator();
    while(it.hasNext())
    {
        ArrayList<Integer> obj = it.next();
        System.out.println(obj);
    }
        System.out.println(triangle.get(25));
        }
}

无论是关于手头的问题还是我对这些数据结构的使用,都会非常感谢任何帮助.

Answer 1

每次在下面调用时,您都不会创建一个新的临时实例,相同的列表将添加到列表中,您要清除它.记住它是添加的列表的引用.

 public static void addToList(int num, ArrayList<ArrayList<Integer>> list)
    //Splits the two parts of the number and inserts the arraylist into the proper arraylist
    {
      //  temp.clear();// this is the issue do below
        ArrayList<Integer> temp = new ArrayList<Integer>();
        int numInt_one = Integer.parseInt(String.valueOf(num).substring(0,2));  
        int numInt_two = Integer.parseInt(String.valueOf(num).substring(2,4));  
        temp.add(numInt_one);
        temp.add(numInt_two);
        list.add(temp);
    }