java - IndexOutOfBoundsException : Index: 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;
        }
    }

当我运行这个时，我收到此错误

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，但我不知道为什么收到此错误。我花了很多时间在这个问题上但没有解决它，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 的元素(似乎为 0)时，会引发异常。

您可以做的是将 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 .