Java Assignment Help

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(this.nameField);
this.add(this.majorField);
this.add(this.opBox);
this.add(processButton);
this.setPreferredSize(new Dimension(300, 180));
// add action listener
this.processButton.addActionListener(handler);
}

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,

"This student has been added into the database!");
}
private void delete() {
empty!");
return;
}
if (!students.containsKey(ID)) {
"Student ID(" + ID + ") does not exist!");
return;
}
/* delete from the database */
this.students.remove(ID);
"This student has been deleted from the database!");
}
private void find() {
empty!");
return;
}
return;
}
/* display the student information */
Student student = students.get(ID);
JOptionPane.showMessageDialog(this, student.toString());
}
private void update() {
empty!");
return;
}

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"});
grades, "Choose grade:", JOptionPane.QUESTION_MESSAGE);
String grade = (String) grades.getSelectedItem();
/* credits */
JComboBox<Integer> credits = new JComboBox<Integer>(
new Integer[] {3, 6});
credits, "Choose credits:", JOptionPane.QUESTION_MESSAGE);
Integer credit = (Integer) credits.getSelectedItem();
/* add to the student */
student.courseCompleted(grade, credit);
"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();
}
}

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