Question

我目前正在开展一个学习项目，我们正在学习使用Arrays of Objects。我一直遇到两个不同的问题，我想谈谈。我正在使用NetBeans IDE以及我在下面提到的所有代码。

首先，在我向数组添加值之后，我尝试使用一个列表按钮，它应该在jtextArea中显示值。弹出没有明显的错误，但是，所有的值都说“null”而不是用户输入的值。由于有5个值，程序显示“null null null null null”。我不确定为什么会这样，任何意见都会受到赞赏。

其次，我试图允许用户根据已存储的5个值之一删除信息。在该程序的情况下，用户必须输入“员工ID”以从程序列表中删除所有所述员工的数据。我在执行此操作时遇到问题，因为您可以在下面的代码中看到。

总结一下：如何更正此随机“空”错误，以便显示插补数据？如何根据idNumber的用户输入有效删除给定索引的值？

要记住的事情： - 我需要使用一个对象数组 - 我对编码很新，所以请原谅我可能的无知 - 任何看似缺失的内容都可能包含在NetBeans代码中，因此可能未包含在内，这是我心中关注的主要代码

以下是代码：

//ArrayList of Objects Declared
ArrayList <employees> list = new ArrayList <employees>();

private void addButtonActionPerformed(java.awt.event.ActionEvent evt) {                                          

        employees e;

        //Declaring Strings
        String idNumber, firstName, lastName, annualSalary, startDate;

        //Reads the input fields
        idNumber = idInput.getText();
        firstName = fNameInput.getText();
        lastName = lNameInput.getText();
        annualSalary = annualInput.getText();
        startDate = startDateInput.getText();

        //Sends input information as a class
        e = new employees(idNumber, firstName, lastName, annualSalary, startDate);

        //If data is missing, the user will receive and error message
        if (idNumber.isEmpty()||firstName.isEmpty()||lastName.isEmpty()||annualSalary.isEmpty()||startDate.isEmpty()){
            infoOutput.setText("Please fill out all catagories!");
        }

        //Otherwise, the information provided will be stored
        else {
        list.add(e);
        infoOutput.setText("");
        infoOutput.setText("Employee data added!");   
        } 
}                                         

private void removeButtonActionPerformed(java.awt.event.ActionEvent evt) {                                             

        //Reset infoOutput
        infoOutput.setText("");

        employees e;

        //Declaring Strings
        String idNumber, firstName, lastName, annualSalary, startDate;

        //Reads the input fields
        idNumber = idInput.getText();
        firstName = fNameInput.getText();
        lastName = lNameInput.getText();
        annualSalary = annualInput.getText();
        startDate = startDateInput.getText();

        //Sends input information as a class
        e = new employees(idNumber, firstName, lastName, annualSalary, startDate);

        //Determines if the requested employee exists in the list
        for (int index = 0; index < list.size(); index++) {

            //If the employee ID is found, their information is removed
            if (list.get(index).toString() == idNumber){
                infoOutput.setText("Employee data removed!");
                list.remove(index);
            }

            //Otherwise, an error message is displayed to the user
            else{
                infoOutput.setText("The employee ID " + idNumber + " was not found!");
            }
        }

}                                            
class employees {
        String idNumber, firstName, lastName, annualSalary, startDate;

        employees(String idNumber, String firstName, String lastName, String annualSalary, String startDate) {

            idNumber = idInput.getText();
            firstName = fNameInput.getText();
            lastName = lNameInput.getText();
            annualSalary = annualInput.getText();
            startDate = startDateInput.getText();
        }
}
private void listButtonActionPerformed(java.awt.event.ActionEvent evt) {                                           

    //Reset temp
    String temp = "";

    //List all of the stored data
    for (int x = 0; x <= list.size()-1; x++) {
        temp = temp + list.get(x).idNumber + " "
                + list.get(x).firstName + " "
                + list.get(x).lastName + " "
                + list.get(x).annualSalary + " "
                + list.get(x).startDate + "\n";
    }
    outputField.setText(temp);
}

感谢您的帮助！

Answer 1

员工的构造函数不初始化实例变量，它初始化参数。例如，将idNumber初始化为

this.idNumber = idNumber;

对剩余的实例变量执行类似的语句。这就是员工类中所有值都为空的原因。

在测试idNumber时，您将使用idNumber比较员工的toString（）。您必须将列表中员工的idNumber与UI中的idNumber进行比较。

if (list.get(index).idNumber.equals(idNumber)) {

最好为员工类中的每个属性创建一个访问者。

Answer 2

以下是我在评论中描述的带有employees方法的getData类。（我还更改了由@downyt更正的构造函数）

class employees {
    String idNumber, firstName, lastName, annualSalary, startDate;
    employees(String idNumber, String firstName, String lastName, String annualSalary, String startDate) {
        this.idNumber = idNumber;
        this.firstName = firstName;
        this.lastName = lastName;
        this.annualSalary = annualSalary;
        this.startDate = startDate;
    }

    String getData(){
        return idNumber + " " + firstName + " " + lastName + " " + annualSalary + " " + startDate;
    }
}

使用此方法，打印代码将更改为类似于此的内容：

for (int x = 0; x < list.size(); x++){
    temp = list.get(x).getData() + "\n";
}
outputField.setText(temp);

如果您愿意，也可以将"\n"放入getData()，将温度更改为

temp += list.get(x).getData();

从Java中的对象数组中删除对象

2 个答案: