java - JComboBox ActionEvent 在 Java 中返回值

Question

我正在尝试将 JComboBox 添加到我的学生计划中，并提供以下选项:新生、大二、大三或大四。选择高级选项时，它应该输出类似“学生已在校学习四年”或初级选项“学生已在校学习三年”的内容。等等...我搜索了论坛并做了一些谷歌搜索，但我无法提供与我在这里尝试做的类似的例子。我将在下面发布代码。任何帮助将不胜感激。谢谢!

学生类(class):

public class Student {
    protected String name;
    protected String address;
    protected double balance;
    protected String major;

    // Constructs fields
    public Student(String name, String address, String major, double balance) {
        this.name = name;
        this.address = address;
        this.major = major;
        this.balance = balance;
    }

    public String setName() {
        return name;
    }

    public String setAddress() {
        return address;
    }

    public double setBalance() {
        return balance;
    }

    public String setMajor() {
        return major;

    }

    public String setStudentInformation() {
        return "\n\tName: " + name + "\n\tAddress: " + address + "\n\tMajor: " + major + "\n\tBalance: " + balance;
    }

    public String toString() {
        return setStudentInformation();
    }
}

经理类:

public class Manager {
    private static Manager thisManager;

    public Student[] students = new Student[50];
    public int studentCounter = 0;

    public GradStudent[] gradStudents = new GradStudent[50];
    public int gradCounter = 0;

    // Private Constructor (Singleton instance method)
    public Manager() {

    }

    // Instance method (Singleton)
    public static Manager instance() {
        if (thisManager == null) {
            return thisManager = new Manager();
        } else {
            return thisManager;
        }
    }

    public Student createStudent(String name, String address, String major,
            double amount) {
        Student c1 = new Student(name, address, major, amount);
        storeStudent(c1);
        return c1;
    }

    private void storeStudent(Student c1) {
        students[studentCounter++] = c1;
    }

    public GradStudent createGradStudent(String name, String address,
            String major, double amount) {
        GradStudent e1 = new GradStudent(name, address, major, amount);
        storeGradStudent(e1);
        return e1;
    }

    private void storeGradStudent(GradStudent g1) {
        gradStudents[gradCounter++] = g1;
    }

    public String listStudents() {
        String temp = "\n\nStudent List\n";

        for (int i = 0; i < studentCounter; i++) {
            temp += "Student: " + students[i].setName() + "\n";
        }

        return temp;
    }

    public String listGrads() {
        String temp = "\n\nGraduate Student List\n";

        for (int i = 0; i < gradCounter; i++) {
            temp += "Graduate Student: " + gradStudents[i].setName() + "\n";
        }

        return temp;
    }

    public String aveBalance() {
        String temp = "\n\nStudent Average Balance: ";
        double sum = 0;

        for (int i = 0; i < studentCounter; i++) {
            sum += students[i].setBalance();
        }

        for (int i = 0; i < gradCounter; i++) {
            sum += gradStudents[i].setBalance();
        }

        return temp + sum / (studentCounter + gradCounter) + "\n";
    }

    public String listCsci() {
        String temp = "\n\nComputer Science Student List\n";

        for (int i = 0; i < studentCounter; i++) {
            if (students[i].setMajor().equals("Computer Science")) {
                temp += "Student: " + students[i].setName() + "\n";
            }
        }

        for (int i = 0; i < gradCounter; i++) {
            if (gradStudents[i].setMajor().equals("Computer Science")) {
                temp += "Graduate Student: " + gradStudents[i].setName() + "\n";
            }
        }

        return temp;
    }
}

GUI 类:

import javax.swing.*;

import java.awt.event.*;
import java.awt.*;
import java.util.Enumeration;

public class GUI extends JFrame implements ActionListener {
    // RadioButtons & ButtonGroup
    private JRadioButton jrbStudent = new JRadioButton("Student");
    private JRadioButton jrbGraduate = new JRadioButton("Graduate Student");
    private ButtonGroup group = new ButtonGroup();

    // JTextFields
    private JTextField name = new JTextField(20);
    private JTextField address = new JTextField(20);
    private JTextField balance = new JTextField(20);
    private JTextField major = new JTextField(20);

    // Submit Button
    private JButton jbtSubmit = new JButton("Submit");

    // echoStudent output area
    private JTextArea echoStudent = new JTextArea(5, 20);

    // Specific Buttons
    private JButton printStudentNames = new JButton("Print Student's Names");
    private JButton printGradStudentNames = new JButton(
            "Print Graduate Student's Names");
    private JButton calcBalance = new JButton(
            "Calculate Average Balance of All Students");
    private JButton compSciMajor = new JButton(
            "Displays Computer Science Major Students");

    // ScrollPane
    private JScrollPane scrollPane = new JScrollPane(echoStudent);

    // Fill and create JComboBox
    private String[] studentYear = { "Freshman", "Sophomore", "Junior", "Senior" };
    private JComboBox<String> jcbo = new JComboBox<String>(studentYear);



    public GUI() {
        super("College Student Information Interface");

        // Creates Panels
        JPanel bottomPanel = new JPanel();
        JPanel topLeftPanel = new JPanel();
        JPanel topRightPanel = new JPanel();

        // Adds Labels, Fields, and Buttons to the topRightPanel
        topRightPanel.setLayout(new GridLayout(7, 2, 5, 5));
        topRightPanel.add(new JLabel("Name:"));
        topRightPanel.add(name);
        topRightPanel.add(new JLabel("Address:"));
        topRightPanel.add(address);
        topRightPanel.add(new JLabel("Major:"));
        topRightPanel.add(major);
        topRightPanel.add(new JLabel("Balance:"));
        topRightPanel.add(balance);
        topRightPanel.add(new JLabel("Submit:"));
        topRightPanel.add(jbtSubmit);
        topRightPanel.add(printStudentNames);
        topRightPanel.add(printGradStudentNames);
        topRightPanel.add(calcBalance);
        topRightPanel.add(compSciMajor);

        // Handles the radioButton group and adds ActionListeners
        jrbStudent.setSelected(true);
        group.add(jrbStudent);
        group.add(jrbGraduate);
        jrbStudent.addActionListener(this);
        jrbGraduate.addActionListener(this);

        // topLeftPanel includes student type with student/gradStudent radio
        // buttons & freshman/sophomore/junior/senior in a combo box
        topLeftPanel.setBorder(BorderFactory
                .createTitledBorder("Which Type of Student Are You?"));
        topLeftPanel.add(jrbStudent);
        topLeftPanel.add(jrbGraduate);
        topLeftPanel.add(jcbo);

        // Adds topLeftPanel and topRightPanel to bottomPanel
        bottomPanel.add(topLeftPanel);
        bottomPanel.add(topRightPanel);

        // Places bottomPanel and scrollPane
        getContentPane().add(BorderLayout.NORTH, bottomPanel);
        getContentPane().add(BorderLayout.CENTER, scrollPane);

        // Adds ActionListeners to the buttons
        jbtSubmit.addActionListener(this);
        printStudentNames.addActionListener(this);
        printGradStudentNames.addActionListener(this);
        calcBalance.addActionListener(this);
        compSciMajor.addActionListener(this);
        echoStudent.setEditable(false);

        // Interface Settings
        setSize(1200, 700);
        setVisible(true);

    }

    // ActionEvent methods to handle interface events
    public void actionPerformed(ActionEvent event) {
        if (event.getSource() == jbtSubmit) {
            if (jrbStudent.isSelected()) {
                Student s1 = Manager.instance().createStudent(name.getText(),
                        address.getText(), major.getText(),
                        Double.parseDouble(balance.getText()));
                echoStudent.append("\n\nCreated Student: " + s1.toString());
            }

            else if (jrbGraduate.isSelected()) {
                GradStudent g1 = Manager.instance().createGradStudent(
                        name.getText(), address.getText(), major.getText(),
                        Double.parseDouble(balance.getText()));
                echoStudent.append("\n\nCreated Graduate Student: "
                        + g1.toString());

            }
        } else if (event.getSource() == printStudentNames) {
            echoStudent.append(Manager.instance().listStudents());
        } else if (event.getSource() == printGradStudentNames) {
            echoStudent.append(Manager.instance().listGrads());
        } else if (event.getSource() == calcBalance) {
            echoStudent.append(Manager.instance().aveBalance());
        } else if (event.getSource() == compSciMajor) {
            echoStudent.append(Manager.instance().listCsci());
        } else if (event.getSource() == jcbo) {

        }
    }

    public static void main(String[] args) {
        new GUI();

    }

}

Answer 1

你可以这样实现。 首先，在 GUI() 构造函数中将 actionListener 添加到 JComboBox jcbo。

jcbo.addActionListener (new ActionListener () {
public void actionPerformed(ActionEvent e) {
String selected=""+jcbo.getSelectedItem();
if(selected.equals("Senior"))
   System.out.println("Student has been in school for four years")
else if(selected.equals("Junior"))
   System.out.println("Student has been in school for three years");
    }
});

像这样，您可以对所有选项执行此操作。代码本身是不言自明的。 即使是这样。我给你一个简短的解释。 当选择 JComboBox 项目时，将执行上述代码。如果选择的是

1. Senior :- Prints Student has been in school for four years.
2. Junior :- Prints Student has been in school for three years.

我想这会对你有帮助。