IndexOutOfBoundsException：索引：0，大小：0 2D Arraylist

Question

I have this code

    ArrayList<ArrayList<Integer>> Pareto_set_List=new ArrayList<ArrayList<Integer>>();
        for(Optimization_Problem.General_Calculation.Get_Another_Solution=0;Optimization_Problem.General_Calculation.Get_Another_Solution<Input.General_Inputs.Monte_Carlo_Step;Optimization_Problem.General_Calculation.Get_Another_Solution++){
        int Count_Location=0;
            for(Optimization_Problem.General_Calculation.Count_year=0;Optimization_Problem.General_Calculation.Count_year<Input.General_Inputs.Analysis_Period;Optimization_Problem.General_Calculation.Count_year++){
    //Run code Calculation not shown here.
    for(int j=0;j<Input.General_Inputs.Num_Of_Ppes;j++){
                Pareto_set_List.get(Optimization_Problem.General_Calculation.Get_Another_Solution).add(EncodingUtils.getInt(solution.getVariable(j)));
            Count_Location++;}
            double[] objectives = solution.getObjectives();
            //System.out.println("Solution " + (1) + ":");
            Pareto_set_List.get(Optimization_Problem.General_Calculation.Get_Another_Solution).add((int) Math.floor(objectives[0])); Count_Location++;
            Pareto_set_List.get(Optimization_Problem.General_Calculation.Get_Another_Solution).add((int) Math.floor(objectives[1])); Count_Location++;
            Pareto_set_List.get(Optimization_Problem.General_Calculation.Get_Another_Solution).add((int) Math.floor(objectives[2])); Count_Location++;
        }
        }
        Optimization_Problem.General_Calculation.Count_year=0;
        }
    }

当我运行它时，我得到了这个错误

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    at java.util.ArrayList.rangeCheck(Unknown Source)
    at java.util.ArrayList.get(Unknown Source)
    at Implementation_Method.main(Implementation_Method.java:53)

我认为数组列表是动态的，但我不知道为什么会收到此错误。我花了很多时间在没有解决它的情况下，非常感谢任何帮助。 提前致谢。

Answer 1

Pareto_set_List.get(Optimization_Problem.General_Calculation.Get_Another_Solution).add(EncodingUtils.getInt(solution.getVariable(j)));

在此之前，您似乎没有向Pareto_set_List 添加任何ArrayList 实例，因此ArrayList 为空。当您尝试检索位于 Optimization_Problem.General_Calculation.Get_Another_Solution（似乎为 0）的元素时，将引发异常。

您可以将ArrayList 添加到Pareto_set_List，如下所示：

Pareto_set_List.add(new ArrayList<Integer>());

您可以找到有用的信息here 和几个链接here。