java - 尝试为 hashmap 赋值时出现空指针异常

Question

package com.assignment;

import java.util.ArrayList;
import java.util.HashMap;



public class Interview {

private HashMap<String,Integer> stateCounts = null;
private HashMap<String,String> stateNames;
private ArrayList<InputData> inputList = null;


public void loadStateNames(String stateKey,String stateName)
{
    stateNames.put(stateKey, stateName);
}


public static void main(String Args[])
{
    Interview interview = new Interview();
    interview.loadStateNames("NY", "New York");
}
}

当我尝试将字符串传递给 loadStateNames 时。我得到一个空指针异常。无法找出导致此错误的原因。

Exception in thread "main" java.lang.NullPointerException
at com.assignment.Interview.loadStateNames(Interview.java:41)
at com.assignment.Interview.main(Interview.java:57)

Answer 1

您尚未初始化 map ，请将其更改为::

private HashMap<String,String> stateNames = new HashMap<String,String>();