在下面的代码中,我尝试将用户的输入作为字符串读取,然后将所述输入存储到 ArrayList 中。我创建了一个单独的方法,该方法应该从 main 中获取用户输入并将其操作到 ArrayList 中。我的问题是,当我尝试将输入数据从我的主方法传递到同一类的单独方法时,我的代码抛出了 NullPointerException。
我收到的错误消息:
SummationPuzzle.convertStr(SummationPuzzle.java:22) 处 SummationPuzzle.main(SummationPuzzle.java:96) 处的线程“主”java.lang.NullPointerException 中的异常
import java.util.*;
public class SummationPuzzle
{
public static ArrayList<Character> fsList;
public static ArrayList<Character> lastW;
public static ArrayList<Character> finaList;
/**
* Reads in 3 words entered by user and converts the first two string into a single <Character> ArrayList
* takes the third string entered and converts it into it's own <Character>ArrayList
* @param firstW
* @param secondW
* @param thirdW
*/
public static void convertStr(String firstW, String secondW, String thirdW)
{
String combined = new String(firstW + secondW);
for(int i = 0; i< combined.length(); i++)
{
fsList.add(combined.charAt(i));
for(int j = 0; j< thirdW.length(); j++)
{
lastW.add(thirdW.charAt(j));
}
}
removeDuplicate(fsList, lastW);
//feeds the resulting lists into the removeDuplicate method
}
/**
* Combines two <Character> ArrayList into a one <Character> ArrayList with single instances of the char
* @param fsList
* @param lastW
*/
public static void removeDuplicate(ArrayList<Character> fsList, ArrayList<Character> lastW)
{
ArrayList<Character> tempList = new ArrayList<Character>();
tempList.addAll(fsList);
tempList.addAll(lastW);
for(char dupLetter : tempList)
{
if(!finaList.contains(dupLetter))
{
finaList.add(dupLetter);
}
}
System.out.println(finaList + "This is the list with duplicates removed");
assignNum(finaList, lastW);
//feeds results into the assignNum method
}
/**
* Assigns a random number to the char that resides at each address in the <Character> ArrayList
* if the First char in the lastW ArrayList is present in the finaList <Character> ArrayList then the program
* assigns that character the value of "1"
* @param finaList
* @param lastW
*/
public static void assignNum(ArrayList<Character> finaList, ArrayList<Character> lastW)
{
char[] assignLetter= new char[finaList.size()];
Random r = new Random();
for(int i = 0; i< assignLetter.length; i++)
{
assignLetter[i] = finaList.get(i);
assignLetter[i] = (char)r.nextInt(assignLetter.length);
System.out.println((long)assignLetter[i]);
if(lastW.get(0).equals(assignLetter[i]))
{
assignLetter[i] = 1;
}
}
System.out.println(assignLetter.toString() + "This is the list with numbers assigned");
}
//main method
public static void main(String[] args)
{
//Receive user input
Scanner userIn = new Scanner(System.in);
System.out.println("Please enter your first word");
String firstW = userIn.next().trim();
System.out.println("Please enter your Second word");
String secondW = userIn.next().trim();
System.out.println("Please enter your Third word");
String thirdW = userIn.next().trim();
//print the summation puzzle
System.out.println(firstW+ " + " + secondW + " = "+ thirdW);
convertStr(firstW, secondW, thirdW);
}
}