The document outlines a Java program for a graphical user interface (GUI) to manage a student database using a hash map. It includes functionalities for inserting, deleting, finding, and updating student records through various input fields and buttons. The program employs Swing components to create the GUI and handle user interactions for managing student details.

2. Hash Map implementation in Java
This program is showing the concept of a GUI implementation for
student database.
import java.util.HashMap;
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
// the GUI for student database management
public class GUI extends JPanel {
private JTextField idField, nameField, majorField;
private JComboBox<String> opBox; /* the operation */
private JButton processButton;
private HashMap<String, Student> students;
public GUI() {
this.students = new HashMap<String, Student>();
// create the fields and add into the GUI
this.idField = new JTextField();
this.nameField = new JTextField();
this.majorField = new JTextField();
this.opBox = new JComboBox<String>(
new String[] {"Insert", "Delete", "Find", "Update"});
this.processButton = new JButton("Process Request");
JLabel[] labels = {
new JLabel("Id:"), new JLabel("Name: "),
new JLabel("Major:"), new JLabel("Choose Selection: ")
};
this.setLayout(new GridLayout(5, 2));
this.add(labels[0]);
this.add(this.idField);
this.add(labels[1]);
this.add(this.nameField);
this.add(labels[2]);
this.add(this.majorField);
this.add(labels[3]);
this.add(this.opBox);
this.add(processButton);
this.setPreferredSize(new Dimension(300, 180));
// add action listener
this.processButton.addActionListener(handler);
}

3. private ActionListener handler = new ActionListener() {
@Override
public void actionPerformed(ActionEvent ae) {
String op = (String) opBox.getSelectedItem();
// call the corresponding function to handle the operation
if ("Insert".equals(op)) {
insert();
} else if ("Delete".equals(op)) {
delete();
} else if ("Find".equals(op)) {
find();
} else if ("Update".equals(op)) {
update();
}
}
};
/* the four functions to manage student database */
private void insert() {
/* validate the input fields */
String ID = this.idField.getText().trim();
if (ID.length() == 0) {
JOptionPane.showMessageDialog(this, "The ID field is
empty!");
return;
}
if (students.containsKey(ID)) {
JOptionPane.showMessageDialog(this, "Student ID(" + ID +
") already exists!");
return;
}
/* make sure name/major are not empty */
String name = this.nameField.getText().trim();
String major = this.majorField.getText().trim();
if (name.length() == 0) {
JOptionPane.showMessageDialog(this, "The name field is
empty!");
return;
}
if (major.length() == 0) {
JOptionPane.showMessageDialog(this, "The major field is
empty!");
return;
}
/* add into the dababase */
Student student = new Student(name, major);
this.students.put(ID, student);
JOptionPane.showMessageDialog(this,

4. "This student has been added into the database!");
}
private void delete() {
/* validate the input fields */
String ID = this.idField.getText().trim();
if (ID.length() == 0) {
JOptionPane.showMessageDialog(this, "The ID field is
empty!");
return;
}
if (!students.containsKey(ID)) {
JOptionPane.showMessageDialog(this,
"Student ID(" + ID + ") does not exist!");
return;
}
/* delete from the database */
this.students.remove(ID);
JOptionPane.showMessageDialog(this,
"This student has been deleted from the database!");
}
private void find() {
/* validate the input fields */
String ID = this.idField.getText().trim();
if (ID.length() == 0) {
JOptionPane.showMessageDialog(this, "The ID field is
empty!");
return;
}
if (!students.containsKey(ID)) {
JOptionPane.showMessageDialog(this,
"Student ID(" + ID + ") does not exist!");
return;
}
/* display the student information */
Student student = students.get(ID);
JOptionPane.showMessageDialog(this, student.toString());
}
private void update() {
/* validate the input fields */
String ID = this.idField.getText().trim();
if (ID.length() == 0) {
JOptionPane.showMessageDialog(this, "The ID field is
empty!");
return;
}
if (!students.containsKey(ID)) {
JOptionPane.showMessageDialog(this,

5. "Student ID(" + ID + ") does not exist!");
return;
}
/* input the credit and grade for the student */
Student student = students.get(ID);
/* letter grade */
JComboBox<String> grades = new JComboBox<String>(
new String[] {"A", "B", "C", "D", "F"});
JOptionPane.showMessageDialog(this,
grades, "Choose grade:", JOptionPane.QUESTION_MESSAGE);
String grade = (String) grades.getSelectedItem();
/* credits */
JComboBox<Integer> credits = new JComboBox<Integer>(
new Integer[] {3, 6});
JOptionPane.showMessageDialog(this,
credits, "Choose credits:", JOptionPane.QUESTION_MESSAGE);
Integer credit = (Integer) credits.getSelectedItem();
/* add to the student */
student.courseCompleted(grade, credit);
JOptionPane.showMessageDialog(this,
"This student has been updated in the database!");
}
// display in a frame
public void display() {
JFrame frame = new JFrame();
frame.setTitle("Project 4");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setContentPane(this);
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
new GUI().display();
}
}