尝试从JDialog框中将项插入数组时出现NullPointerException

时间：2014-11-12 05:19:48

标签： java nullpointerexception instance jdialog

正如它所述，当我尝试通过我的JDialog弹出窗口将一个项目插入一个对象数组时，我得到一个NullPointerException。我重新编写了一个现有应用程序来创建JDialog，它从另一个当前名为Project6()的应用程序类打开。名为JDialog的{​​{1}}类在作为独立GUI运行时（在我将其设为ProcessRec()之前）运行良好。

在这种情况下，我的堆栈跟踪相当无用，因为它只指向尝试将数据插入数组的方法（就像我之前说的那样，之前工作正常）和与它们对应的GUI按钮。

JDialog的构造函数接受一个ProcessRec()对象，它与创建我的对象数组的类（这是我定义的另一个类的对象数组ToolWarehouse()）相匹配。 

ToolItem()

当它自己运行时，public ProcessRec(ToolWarehouse tools) 构造函数params为空（默认）。

当ProcessRec()作为独立的GUI运行以将数据输入到数组中时，我会使用默认构造函数创建一个对象，如下所示：

ProcessRec()

然后我会使用它的方法ToolWareHouse tools = new ToolWarehouse(); 将数据输入到数组中。

现在它是insert()，但我被指示改为：

JDialog

然而，这会导致ToolWarehouse tools; 因为，我猜，编译器指向的是不存在的对象。当我在NullPointerException中创建一个新对象时，正如我在独立时所做的那样，我不再得到ProcessRec()。但是，当我尝试使用exception将数据存储到数组中时，它不起作用并且无法找到数据（尽管我收到提示说插入成功）。

我对类的实例知之甚少，但我假设我的数据未显示的原因是因为它使用的是insert()类的完全不同的实例？格式是：

ToolWarehouse()

接受之前使用的类的相同实例？我可能会离开这里，所以我希望有人可以帮助我理解可能发生的事情和为什么。

如果需要更多信息我道歉，我会添加任何必要的信息。代码有点冗长，我不想占用空间。万分感谢。

编辑：这是public ProcessRec(ToolWarehouse tools) 类，它创建了ProcessRec()框，以及与其对应的一些方法。

JDialog

创建数组的ToolWarehouse类：

public class ProcessRec extends JDialog
{
     //global declarations
     private JButton insertBtn;
     private JButton deleteBtn;
     private JButton displayBtn;
     private JButton hideBtn;
     private JButton clearBtn;

     private JTextField toolFld;
     private JTextField idFld;
     private JTextField priceFld;
     private JTextField qualityFld;
     private JTextField numInStockFld;
     private JTextField messageFld;

     private JLabel messageLbl;

     private Font f1 = new Font("serif", Font.BOLD, 24);
     private Font f2 = new Font("serif", Font.PLAIN, 18);

     private Container c = getContentPane();

     private String input = "";
     private String toolInput = "";

     private int responseCode = 0;
     private int idInput = 0;
     private int qualityInput = 0;
     private int numInStockInput = 0;

     private double priceInput = 0.0;

     private ToolWarehouse tools = new ToolWarehouse();

    //constructor for GUI elements and event listeners
    public ProcessRec(ToolWarehouse tools)
    {
         setTitle("Project1");
         setSize(520,450);
             c.setLayout(new FlowLayout());

             JLabel title = new JLabel("Tiny Tim's Tool Warehouse, Inc.");
         title.setFont(f1);
         c.add(title);

         JTextField toolLbl = new JTextField("Enter tool name:", 15);
         toolLbl.setEditable(false);
         c.add(toolLbl);

         toolFld = new JTextField(25);
         c.add(toolFld);

         JTextField idLbl = new JTextField("Enter ID:", 15);
         idLbl.setEditable(false);
         c.add(idLbl);

         idFld = new JTextField(25);
         c.add(idFld);

         JTextField priceLbl = new JTextField("Base Price:", 15);
         priceLbl.setEditable(false);
         c.add(priceLbl);

         priceFld = new JTextField(25);
         c.add(priceFld);

         JTextField qualityLbl = new JTextField("Enter Quality:", 15);
         qualityLbl.setEditable(false);
         c.add(qualityLbl);

         qualityFld = new JTextField(25);
         c.add(qualityFld);

         JTextField numInStockLbl = new JTextField("Enter Number in Stock:", 15);
         numInStockLbl.setEditable(false);
         c.add(numInStockLbl);

         numInStockFld = new JTextField(25);
         c.add(numInStockFld);

         insertBtn = new JButton("Insert");
         c.add(insertBtn);

         deleteBtn = new JButton("Delete");
         c.add(deleteBtn);

         displayBtn = new JButton("Display");
         c.add(displayBtn);

         hideBtn = new JButton("Hide");
         c.add(hideBtn);

         clearBtn = new JButton("Clear");
         c.add(clearBtn);

         JLabel messageLbl = new JLabel("Messages:");
         messageLbl.setFont(f2);
         c.add(messageLbl);

         messageFld = new JTextField(30);
         c.add(messageFld);

         //button listeners
         insertBtn.addActionListener(new EventListener());
         deleteBtn.addActionListener(new EventListener());
         displayBtn.addActionListener(new EventListener());
         hideBtn.addActionListener(new EventListener());
         clearBtn.addActionListener(new EventListener());

    } //end constructor  

    public String getToolRecords(int index)
    {
            return tools.getRecord(index);
    }

    public int getNumberOfItems()
    {
            return tools.getNumberOfItems();
    }

//Action Listener 
private class EventListener implements ActionListener
{
    public void actionPerformed(ActionEvent ev)
    {
            if (ev.getSource() == insertBtn)
            {
                toolInput = toolFld.getText();

                input = idFld.getText();
                idInput = Integer.parseInt(input);

                input = priceFld.getText();
                priceInput = Double.parseDouble(input);

                input = qualityFld.getText();
                qualityInput = Integer.parseInt(input);

                input = numInStockFld.getText();
                numInStockInput = Integer.parseInt(input);

                responseCode = tools.insert(qualityInput, toolInput, idInput, numInStockInput,
                                                    priceInput);

                if (responseCode == 1)
                {
                    messageFld.setText(idInput + " - Successful insertion");
                }
                else if (responseCode == 0)
                {
                    messageFld.setText(idInput + " - Array is full");
                }
                else if (responseCode == -1)
                {
                    messageFld.setText(idInput + " - Duplicate/Invalid ID");
                }

                if (tools.getNumberOfItems() < 10)
                {   
                    JOptionPane.showMessageDialog(null, "Tool Name: " + toolInput  
                                + "\nTool ID: " + idInput + "\nTool Base Price: " + "$" + priceInput
                                + "\nQuality: " + qualityInput + "\nNumber In Stock: " 
                                + numInStockInput, "Insert Review", JOptionPane.INFORMATION_MESSAGE);
                }
                else if (tools.getNumberOfItems() == 10)
                {
                    JOptionPane.showMessageDialog(null, "The array is full, please delete an entry",
                                                  "Insert Review", JOptionPane.INFORMATION_MESSAGE);
                }

            }//end insert button

            else if (ev.getSource() == deleteBtn)
            {
                input = idFld.getText();
                idInput = Integer.parseInt(input);

                responseCode = tools.delete(idInput);

                if (responseCode == 1)
                {
                    messageFld.setText(idInput + " - Successful deletion");
                }
                else if (responseCode == -1)
                {
                    messageFld.setText(idInput + " - ID not found");
                }

            }//end delete button

            else if (ev.getSource() == displayBtn)
            {
                tools.display();
            }

            else if (ev.getSource() == hideBtn)
            {
                //setState(JFrame.ICONIFIED);
            }

            else if (ev.getSource() == clearBtn)
            {
                qualityFld.setText(null);
                toolFld.setText(null);
                idFld.setText(null);
                numInStockFld.setText(null);
                priceFld.setText(null);

                messageFld.setText(null);

                repaint();

            }//end clear button

    }//end actionPerformed

}//end ActionListener

}//end Project1

我正在处理的当前部分，它从public class ToolWarehouse { //Global declarations private int numberOfItems = 0; private int index = 0; private int returnCode = 0; protected ToolItem[] toolArray = new ToolItem[10]; public ToolWarehouse() { numberOfItems = 0; //creating the array of ToolItems for (int i = 0; i < toolArray.length; i++) { toolArray[i] = new ToolItem(); System.out.println(toolArray[i]); } }//end constructor public int searchArray(int id) { for (index = 0; index < toolArray.length; index++) { if (toolArray[index].getToolID() == id) { System.out.println("ID found at location " + index); return index; } } return -1; }//end searchArray public int insert(int quality, String name, int id, int numInStock, double price) { returnCode = searchArray(id); if (numberOfItems == 10) { System.out.println("Array is full"); return 0; } else if (returnCode == -1) { boolean oK = toolArray[numberOfItems].assign(quality, name, id, numInStock, price); if (oK == true) { System.out.println("Successful insertion"); numberOfItems++; return 1; } } return -1; }//end insert public int delete(int ID) { returnCode = searchArray(ID); if (returnCode != -1) { toolArray[returnCode] = new ToolItem(); for (index = returnCode; index < numberOfItems; index++) { toolArray[index] = toolArray[index + 1]; } numberOfItems--; System.out.println("Successful deletion"); return 1; } else System.out.println("ID not found"); return -1; }//end delete public void display() { for (index = 0; index < numberOfItems; index++) { toolArray[index].calcAdjustedPrice(); toolArray[index].display(); } }//end display public String getRecord(int index) { return "Tool Name: " + toolArray[index].getName() + "| Tool ID: " + toolArray[index].getToolID() + "| Tool Quality: " + toolArray[index].getQuality() + "| Number in Stock: " + toolArray[index].getNumberInStock() + "| Tool Price: " + toolArray[index].getPrice(); }//end getRecord public int getNumberOfItems() { return numberOfItems; } }//end ToolWarehouse 类调用insert()，但不正确插入到我正在处理的数组中使用默认构造函数创建ToolWarehouse()类的对象时（即使我的println调试语句指示它）：

ToolWarehouse()

1 个答案:

答案 0 :(得分：1)

实际上，在尝试使用对象之前，必须确保对象已初始化。你把

ToolWarehouse tools;

作为类变量，在对话框中你可以说

tools = new ToolWareHouse();

创建对象并开始使用它。但也许更好的方法是直接将其初始化为类变量。例如写

ToolWarehouse tools = new ToolWareHouse();

在班级的顶部。 （所以它是一个类变量，并且在整个班级中都是已知的）

您没有向我们展示太多代码，因此很难说出确切的问题是什么。但正如你所说，你没有初始化你的对象，所以当你试图将它传递给另一个方法＆amp;时，你必须得到一个nullPointerException。用它。

相关问题
最新问题