Question

我正在NSGA-II算法中实现非支配排序子程序。以下是代码的初始部分：

 public ArrayList<ArrayList<AttStrategy>> nondominatedSorting     
   (ArrayList<AttStrategy> StrategyPopulation, double max_rho_mal, double p_max) {

    int i = 0, p, q;
    int [] domination_count = new int[StrategyPopulation.size()];

    ArrayList<AttStrategy> dominated_strategies = new ArrayList<>();
    ArrayList<AttStrategy> dominating_strategies = new ArrayList<>();
    ArrayList<ArrayList<AttStrategy>> dominated_strategies_list = new ArrayList<>();
    ArrayList<ArrayList<AttStrategy>> pareto_strategies = new ArrayList<>();

    while(i < StrategyPopulation.size()) {
        int j = 0;
        domination_count[StrategyPopulation.get(i).getId()] = 0;
        dominated_strategies.clear();
        for (j = i+1; j < StrategyPopulation.size(); j++){
            if (constraintDominated(StrategyPopulation.get(i), StrategyPopulation.get(j), max_rho_mal, p_max))
                dominated_strategies.add(StrategyPopulation.get(j));
            else if (constraintDominated(StrategyPopulation.get(j), StrategyPopulation.get(i), max_rho_mal, p_max))
                domination_count[StrategyPopulation.get(i).getId()] += 1;
        }
        if (domination_count[StrategyPopulation.get(i).getId()] == 0) {
            dominating_strategies.add(StrategyPopulation.get(i));
        }
        dominated_strategies_list.add(StrategyPopulation.get(i).getId(), dominated_strategies);

        //values getting stored in the arraylist
        System.out.println("Size of  " + StrategyPopulation.get(i).getId() + ":  " + dominated_strategies_list.get(i).size());
        i = i + 1;
    } //while-loop ends
    //values getting reset to 0.
    System.out.println("********Outside the loop*********");    
    for(i = 0; i < dominated_strategies_list.size(); i++){
        System.out.println("Size of  " + i + ":  " + dominated_strategies_list.get(i).size());
    }
    //.............................................
}

我遇到的问题是2-D arraylist dominated_strategies_list 。这个arraylist正在while循环中填充，但是一旦在循环外部使用它，所有值都将重置为0.但是，其他arraylists和在循环内更新的数组会将它们的值保留在循环之外。因此，我不能在子例程的后面部分使用这个arraylist（ dominated_strategies_list ）。我在哪里弄错了？建议一些可能的解决方案。

Answer 1

您的问题是，您只有一个dominated_strategies列表，您可以重复填写并清除。

该行

dominated_strategies_list.add(StrategyPopulation.get(i).getId(), dominated_strategies);

只会将此单个列表的引用添加到dominated_strategies_list，它不会复制dominated_strategies列表，因此在下一轮循环中，dominated_strategies.clear();会丢弃您之前的结果

解决方案是替换

dominated_strategies.clear();

与

dominated_strategies = new ArrayList<>();

Answer 2

在每次迭代中，您都要清除引用的ArrayList，而不是尝试创建新的ArrayList。

以下是展示错误和解决方案的代码的简化示例。

public static void main(String[] args){        
    //Initialize stuff
    ArrayList<Integer> dom_strat = new ArrayList<>();
    ArrayList<ArrayList<Integer>> dom_list = new ArrayList<>();
    dom_strat.add(5);
    dom_strat.add(3);

    //Add arrayList
    dom_list.add(dom_strat);

    //Print
    System.out.println("Before clear");
    for(ArrayList<Integer> aList:dom_list){
        for(Integer i: aList){
            System.out.println(i);
        }
    }
    //Clear referenced arrayList dom_list
    dom_strat.clear();
    //Print
    System.out.println("After clear");
    for(ArrayList<Integer> aList:dom_list){
        for(Integer i: aList){
            System.out.println(i);
        }
    }


     //Initialize again and apply the fix
    dom_strat = new ArrayList<>();
    dom_list = new ArrayList<>();
    dom_strat.add(5);
    dom_strat.add(3);

    //Add arrayList 
    dom_list.add(dom_strat);

    //Instead of clear, create a new arrayList
     dom_strat = new ArrayList<>();

     //Print
    System.out.println("After applying the fix");
    for(ArrayList<Integer> aList:dom_list){
        for(Integer i: aList){
            System.out.println(i);
        }
    }
}

2-d arraylist在while循环外重置为0

2 个答案: