我正在创建一个证券交易所类型的程序，到目前为止，我的输入已经正常工作，因此它可以正确地接受用户的命令。然而，它对输入的作用并没有按预期工作。我感到困惑的第一件事是为什么在我运行代码时它会抛出 NullPointerException。
基本上，该程序将输入 3 个内容，然后是它们之间的空格。因此，例如，我想以每股 20 美元的价格购买 30 股，我会输入如下输入：
b 30 20
然后它将它分成 3 个部分并将其存储到一个数组中。之后它将比较数组的第一个索引以查看程序应该做什么，在本例中它将购买，因此它将调用购买方法并将份额数量和份额值存储到我的 CircularArrayQueue 中。
它获取存储到节点中的份额值和份额数量，但是当我尝试使用我的 CirularArrayQueue 调用入队方法以将节点存储到队列中时，它给了我一个 NullPointerException。
我遇到的另一个问题是程序的终止。当程序看到输入的第一个索引值为“q”时，程序应该终止。我做了一个while循环，说明当布尔退出为假时它将循环。然后在 while 循环中，我做了一个 if 语句来检查 stockParts[0] 的值是否为“q”。如果是这样，它会将 quit 的值更改为 true 以便它可以结束循环，但由于某种原因它没有终止并且它仍在循环。
几个小时以来，我一直在为这些问题摸不着头脑，但我似乎找不到问题的根源。有人可以帮助我吗？以下是我的主类和 CircularArrayQueue 类的代码：
import java.util.Scanner;
import java.lang.Integer;
public class StockTran {
String command = "";
String[] stockParts = null;
CircleArrayQueue Q;
boolean quit = false;
public StockTran(String inputCommand) {
try {
Scanner conReader = new Scanner(System.in);
this.command = inputCommand.toLowerCase();
this.stockParts = command.split("\\s"); // splits the input into three parts
buyShares(Integer.parseInt(stockParts[1]), Integer.parseInt(stockParts[2])); //testing purpose only
while (quit == false) {
if (this.stockParts[0] == "q") { // ends transaction and terminates program
System.out.println("Share trading successfully cancelled.");
quit = true;
}
if (this.stockParts == null || this.stockParts.length > 3) {
throw new Exception("Bad input.");
}
if (stockParts[0] == "b") { // checks to see if it is a buying of shares
int shares = Integer.parseInt(stockParts[1]); // stores share amount
int value = Integer.parseInt(stockParts[2]); // stores selling value
buyShares(shares, value); // calls buyShares method and adds share to queue
}
else if (stockParts[0] == "s") { // checks to see if it is a selling of shares
int shares = Integer.parseInt(stockParts[1]); // stores share amount
int value = Integer.parseInt(stockParts[2]); // stores selling value
sellShares(shares, value); // calls sellShares method
}
else if (stockParts[0] == "c") { // checks to see if it is capital gain
capitalGain(); // calls capitalGain and calculates net gain
}
System.out.println("Enter your next command or press 'q' to quit: ");
command = conReader.nextLine().toLowerCase();
stockParts = command.split("\\s");
}
} catch (Exception e) {
e.printStackTrace();
}
}
public void buyShares(int shareAmout, int shareValue) { // takes in share total and values for each share
Node temp = new Node(shareAmout, shareValue); // stores values into node
try {
Q.enqueue(temp); // enqueues the node into the CircularArrayQueue
//System.out.println(Q.toString());
} catch (FullQueueException e) {
e.printStackTrace();
}
}
public void sellShares(int shareAmount, int sharePrice) { // ToDo
}
public int capitalGain() { // ToDo
return 0;
}
public static void main(String[] args) {
String inputCommand = "";
Scanner mainReader = new Scanner(System.in);
System.out.println("Enter 'b' to purchase share, 's' to sell share, 'c' for capital gain, or 'Q' to quit: ");
inputCommand = mainReader.nextLine();
StockTran tran = new StockTran(inputCommand);
}
}
public class CircleArrayQueue implements Queue {
protected Node Q[]; // initializes an empty array for any element type
private int MAX_CAP = 0; // initializes the value for the maximum array capacity
private int f, r;
public CircleArrayQueue(int maxCap) {
MAX_CAP = maxCap;
Q = new Node[MAX_CAP]; // sets Q to be a specific maximum size specified
f = 0; // sets front value to be 0
r = 0; // sets rear value to be 0;
}
public int size() {
return (MAX_CAP - f + r) % MAX_CAP; // returns the size of the CircularArrayQueue
}
public boolean isEmpty() { // if front and rear are of equal value, Queue is empty
return f == r;
}
public Node front() throws EmptyQueueException { // method to get the front value of the CircularArrayQueue
if (isEmpty()) throw new EmptyQueueException("Queue is empty.");
return Q[f]; // returns object at front of CircularArrayQueue
}
public Node dequeue() throws EmptyQueueException { // method to remove from the front of the CircularArrayQueue
if (isEmpty()) throw new EmptyQueueException("Queue is empty.");
Node temp = Q[f]; // stores front object in local variable
Q[f] = null; // sets the value to be null in the array
f = (f + 1) % MAX_CAP; // sets the new front value to be this
return temp; // returns the object that was originally in the front
}
public void enqueue(Node element) throws FullQueueException { // method to add to the end of the CircualarArrayQueue
if (size() == MAX_CAP - 1) throw new FullQueueException("Queue has reached maximum capacity.");
Q[r] = element; // stores the new element at the rear of array
r = (r + 1) % MAX_CAP; // sets the new rear value to be the location after element insertion
}
}