Java - 打印字符串数组的数组列表

Question

我对 Java 很陌生，有一个问题。这是家庭作业，所以我不喜欢任何直接的答案。谢谢!

我正在研究玩扑克的遗传算法。我想创建一个字符串数组的 arrayList。字符串数组将保存一轮中每手可能的牌局。为了确保它正常工作，我现在想做的是运行我的方法并打印出结果。这是我的练习课(这只是作业的一小部分):::

import java.util.ArrayList;
import java.util.Arrays;


public class Play 
{

    GeneticAlg start;
    ArrayList<Object> pop;

    public static void main(String[] args) 
    {
        GeneticAlg start = new GeneticAlg();
        ArrayList<String[]> pop = start.initializePopulation();

        for(String[] arr: pop)
        {
            System.out.println(Arrays.toString(arr));
        }

    }

}

import java.util.ArrayList;
import java.util.Random;


public class GeneticAlg 
{
    ArrayList<String[]> population;
    int[] populationScores;
    String[] chromosome;
    int generation;
    int index;

    public GeneticAlg()
    {

    }

    public ArrayList<String[]> initializePopulation()
    {
        ArrayList<String[]> population = new ArrayList<String[]>();

        for (int i = 0; i < 20; i++)
        {
            Random generator = new Random();
            String[] choices = {"bet","raise","call","check"};
            chromosome = new String[33];

            for (int j = 0; j < 33; j++)
            {
                if (j < 6) //first and second round possible hands)
                {
                    index = generator.nextInt((choices.length)-1); 
                    chromosome[j] += choices[index];
                }

                else //third, fourth, and fifth round possible hands)
                {   
                    index = generator.nextInt(choices.length);
                    chromosome[j] += choices[index];
                }
            }

            population.add(chromosome); 
        }

        return population;
    }

}

现在，它正在打印数组，但每个条目如下所示:

[nullcall, nullraise, nullbet, nullraise, nullcall, nullraise,....

我希望它只返回前面没有空的移动。任何建议表示赞赏。谢谢!

预计到达时间:我修复了两行连接错误，但它仍然在每个命令前面打印“null”。有什么建议吗？

修复错误后的代码:

import java.util.ArrayList;
import java.util.Arrays;


public class Play 
{

    GeneticAlg start;
    ArrayList<Object> pop;

    public static void main(String[] args) 
    {
        GeneticAlg start = new GeneticAlg();
        ArrayList<String[]> pop = start.initializePopulation();

        for(String[] arr: pop)
        {
            System.out.println(Arrays.toString(arr));
        }

    }

}

import java.util.ArrayList;
import java.util.Random;


public class GeneticAlg 
{
    ArrayList<Object> population;
    String[] choices;
    int[] populationScores;
    String[] chromosome;
    int generation;
    int index;

    public GeneticAlg()
    {

    }

    public ArrayList<Object> initializePopulation()
    {
        population = new ArrayList<Object>();

        for (int i = 0; i < 20; i++)
        {
            Random generator = new Random();

            for (int j = 0; j < 24; j++)
            {
                if (j < 6) //first and second round possible hands)
                {
                    choices[0]= "bet";
                    choices[1]= "raise";
                    choices[3]= "call";

                    index = generator.nextInt(choices.length); 
                    chromosome[j] = choices[index];
                }

                else //third, fourth, and fifth round possible hands)
                {
                    choices[4] = "check";

                    index = generator.nextInt(choices.length);
                    chromosome[j] = choices[index];
                }
            }

            population.add(chromosome); 
        }

        return population;
    }

}

Answer 1

对象数组(例如Stirng)在开始时用null值填充，所以这样做

chromosome[j] += choices[index];

与

相同

chromosome[j]  = chromosome[j] + choices[index];

与

相同

chromosome[j]  = null + choices[index];

因此，您将 null 与 choices[index]; 连接起来，例如为您提供 nullbet。

要解决这个问题，只需使用 = 而不是 +=。