找不到符号 charAt(int)？

Question

有人可以告诉我我做错了什么吗？

我正在尝试访问地图并将以字母 "N" 开头的键放入数组中。但是，我收到一个 Cannot find symbol error referenced to charAt(int)? Intellij 建议我为 chartAt?

创建一个摘要 class

import java.util.Map;
public class RoadNetwork {

    String[] nodeList;

    public void storeNodes(Map<String, Element> result) {

        int counter =0;
        nodeList = new String[result.size()];

        //Cycle through Map to find elements which are Nodes
        for (int i = 0; i < result.size(); i++) {
            //if Node, then add it to array
            if (result.get(i).charAt(0) == "N") {
                nodeList[i] = String.valueOf(result.get(i));
                counter++;
            }
        }
        System.out.println("Nodes Array Length" + counter);
    }
}

Answer 1

似乎有问题

if (result.get(i).charAt(0) == "N") {

可能您想要检索键但是 get() 方法 returns 值，它是类型 Element，没有方法 charAt()。

您可以尝试类似的方法：

for (String key:result.keySet()) {
        //if Node, then add it to array
        if (key.charAt(0) == 'N') { //'N' and not "N"
            nodeList[i] = String.valueOf(result.get(key));
            counter++;
        }
    }

Answer 2

您的地图将键作为字符串，并且您在行中传递了 int if (result.get(i).charAt(0) == "N") { 所以不是传递 result.get(int) 而是传递 result.get(String)

要检查从 N 开始的键，请执行以下操作：

整数计数器=0； nodeList = new String[result.size()];

//Cycle through Map to find elements which are Nodes
int i = 0;
    //if Node, then add it to array
  for(String key : result.keySet())
  {
  if (key.charAt(0) == 'N') {
        nodeList[i] = key;
        counter++;
    }
  }

System.out.println("Nodes Array Length" + counter);

找不到符号 charAt(int)？

Cannot find symbol charAt(int)?

java

arrays

maps

charat