Question

我正在编写一个程序，用户在JTextField中输入一堆值，然后是另一个JTextField，然后是另一个，等等。即每个JTextField应包含自己的一组值，我需要一个包含这些值的ArrayLists的ArrayList 。

我的问题是它输出的Arraylist包含一组ArrayLists，所有的值都为null。

我稍后也会添加第三个维度，但如果我可以使用它，这应该相对容易。

以下是我尝试使用的方法的简化测试版本：

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

public class Test {
    public static void main(String args[]) {

    ArrayList<Float> temp = new ArrayList<>();                                  //holds each float parsed from an ArrayList of strings
    ArrayList<ArrayList<Float>> output = new ArrayList<>();                     //holds each set of floats
    ArrayList<String> items;                                                    //the string before its parsed into floats

    String s = "1,2,3,4,5,6";                                                   //testing values

    for (int i = 0; i <= 10; i++) {                                             //10 is a random testing number
        //In the real version s changes here
        items = new ArrayList<String>(Arrays.asList(s.split("\\s*,\\s*"))); //split strings by comma accounting for the possibility of a space

        for (String b : items) {                                                //parse each number in the form of a string into a float, round it, and add it to temp
            temp.add((float)((long)Math.round(Float.valueOf(b)*10000))/10000);  
        } //End parsing loop

        output.add(temp);                                                       //put temp in output
        temp.clear();                                                           //clear temp
    } //End primary loop

    System.out.println(output);                                                 //output: [[], [], [], [], [], [], [], [], [], [], []]
}

}

Answer 1

这是因为你不断清除临时arraylist。

在for循环中创建ArrayList<Float> temp = new ArrayList<>();并且不要清除它。

for (int i = 0; i <= 10; i++) {                                             //10 is a random testing number
    //In the real version s changes here
    items = new ArrayList<String>(Arrays.asList(s.split("\\s*,\\s*"))); //split strings by comma accounting for the possibility of a space

    // create this inside so you have a new one for each inner list
    ArrayList<Float> temp = new ArrayList<>(); 
    for (String b : items) {                                                //parse each number in the form of a string into a float, round it, and add it to temp
        temp.add((float)((long)Math.round(Float.valueOf(b)*10000))/10000);  
    } //End parsing loop

    output.add(temp);  

    // don't clear
    //temp.clear();                                                           //clear temp
} //End primary loop

将一组字符串转换为已解析的浮点数的多维数组

1 个答案: