Inspect one character
char stores one UTF-16 code unit. Character provides utility methods such as isDigit, isLetter, and case conversion.
Industry: checking input characters, parsing codes, and text transformations.
Week 12–15 · Interactive lecture companion
From Java basics
to real-world apps.
Explore how Java handles text, validates input, persists data, serializes objects, and builds desktop interfaces. Learn by changing values, running mini-simulations, and connecting each concept to software used in the IT industry.
Learning approach: try first, observe the result, then read the explanation. Examples are teaching simulations; browser demos do not execute Java code.
String input = "Build";
StringBuilder app = new StringBuilder(input);
app.append(" something");
System.out.println(app);03Learning modules
10+Interactive experiments
06Swing components
0%Knowledge check score
Module 01 · Text processing
Strings, Characters & Regular Expressions
Applications receive text constantly: names, search queries, form fields, log messages, and identifiers. Correct text handling improves reliability, usability, and security.
Immutable text
A String cannot be changed after creation. Methods such as concat return a result; they do not mutate the original object.
Industry: safer sharing of text values, configuration, and identifiers.
Build text efficiently
StringBuilder is mutable. Its append, insert, delete, and reverse methods update a character sequence.
Industry: building reports, CSV output, and repeated string changes.
Experiment A — String vs StringBuilder
Change the starting text and append a phrase. Watch which value changes.
Original / result
Original: Java
StringBuilder: Java
Concept:
s.concat("!") returns a new String. If its return value is not assigned, s remains unchanged. sb.append("!") changes the builder.String s = "Java";
s.concat("!"); // s is still "Java"
s = s.concat("!"); // now s is "Java!"
StringBuilder sb = new StringBuilder("Java");
sb.append("!"); // sb now contains "Java!"
Experiment B — Character inspector
Enter one character to explore common Character checks.
Letter: true · Digit: false · Uppercase: true
Character.isLetter(c)
Character.isDigit(c)
Character.isUpperCase(c)
Character.toLowerCase(c)
Java char represents a UTF-16 code unit, not every possible Unicode symbol as one unit. Some symbols require a surrogate pair.
Experiment C — Split into tokens
Tokenization divides a string into smaller pieces. Common use: parsing CSV-like input, tags, or delimited records. Production CSV needs a CSV parser when quoting/escaping rules apply.
applebananaorange
String[] tokens = text.split(",");
for (String token : tokens) {
System.out.println(token);
}
Experiment D — Regex pattern tester
Regex describes a pattern. Try the supplied pattern and input; the demo uses browser regex syntax to illustrate the idea.
Ready to test.
Important: client-side validation improves feedback but is not a security boundary. Validate on the server too. A regex email check only checks a format, not whether an address exists.
Method quick reference
length()
number of UTF-16 code units
charAt(i)
unit at index i
substring(a,b)
from a up to, not including, b
indexOf(x)
first matching index or -1
equals(x)
content equality
compareTo(x)
lexicographic comparison
For Java strings, use
equals() to compare content; == checks whether references point to the same object.Module 02 · Persistence
Files, Streams & Object Serialization
Programs need durable storage so data survives after the application closes. RAM is volatile; files and other storage are designed for persistence.
01 · In-memoryData lives in variables/RAM while the program runs. Closing the process usually loses it.
02 · File I/ORead bytes or characters from a source, or write data to a destination. Choose text or binary APIs appropriately.
03 · Persistent workflowSave records, logs, exports, and settings. Handle errors, permissions, encoding, and resource cleanup.
Experiment E — Stream simulator
Simulate writing and reading a text file. The browser keeps this demo in page memory only; it does not write to your computer.
File state
No file written yet.
Activity log
Waiting for an action…
try (BufferedWriter writer =
Files.newBufferedWriter(path)) {
writer.write(content);
}
Use try-with-resources in modern Java to close streams reliably, including when an exception occurs.
Java I/O toolbox
Choose a task to see an appropriate family of APIs.
Text files
FileReader, FileWriter, BufferedReader, and BufferedWriter work with character data. Set an explicit charset for predictable text encoding.
Package guide:
java.io contains classic stream and reader/writer APIs. java.nio.file provides Path, Files, and directory/file operations.Experiment F — File metadata
Explore the kind of metadata a file utility might show. Values below are illustrative, not actual files on your device.
No metadata loaded.
Path path = Paths.get("data.txt");
long size = Files.size(path);
FileTime created = (FileTime)
Files.getAttribute(path, "creationTime");
Real metadata calls can throw I/O or permission exceptions. Check the exact API and platform behavior.
Experiment G — Serialization lifecycle
Serialization converts an object graph into a byte representation. In Java, Serializable marks eligible classes; object streams write/read the representation.
Object exists in memory only.
try (ObjectOutputStream out =
new ObjectOutputStream(
new FileOutputStream("object.ser"))) {
out.writeObject(student);
}
Security note: do not deserialize untrusted data casually. Java native serialization can create security risks; use safer, explicitly designed data formats for many modern systems.
Experiment H — JFileChooser
JFileChooser lets a desktop Java app ask the user to select a file or directory. Simulate the decision flow.
Select a sample file:
No file selected.
Waiting for selection.
JFileChooser chooser = new JFileChooser();
int result = chooser.showOpenDialog(null);
if (result == JFileChooser.APPROVE_OPTION) {
File selected = chooser.getSelectedFile();
}
Real-world design challenge
A desktop inventory tool must save item records, load them on startup, and let a user choose an export destination.
Module 03 · Desktop interfaces
Swing GUI Components
Graphical user interface components turn program logic into controls people can understand and operate. Good UI design makes tasks discoverable, consistent, and efficient.
Continuous values
Select a numeric value within a range. Useful for volume, brightness, zoom, or threshold controls.
Context actions
Offer relevant actions near the selected item, often on right-click. Keep essential actions discoverable elsewhere too.
Window workspace
Support multiple internal windows inside a main window—an MDI-style workspace for specialized desktop tools.
Organize sections
Separate related content, such as Home, Settings, and Help, without opening a new top-level window for every section.
Linear alignment
Arrange components vertically with Y_AXIS or horizontally with X_AXIS.
Design for the user
Match the control to the task, provide feedback, support keyboard use, and avoid hiding critical actions in context menus.
Experiment I — JSlider simulator
Drag the slider to change a simulated system volume. This mimics the interaction; Java Swing code is shown below.
Balanced output
JSlider slider = new JSlider(0, 100, 50);
slider.addChangeListener(e -> {
int value = slider.getValue();
// update volume display
});
Experiment J — JPopupMenu simulator
Right-click the item below (or use the button for touch devices) to open contextual actions.
📄 project.java
Right-click this workspace to open a simulated context menu.
No action selected.
JPopupMenu popup = new JPopupMenu();
popup.add(new JMenuItem("Refresh"));
popup.add(new JMenuItem("Settings"));
// component.setComponentPopupMenu(popup);
Experiment K — JTabbedPane
Click each tab. Tabs organize related views in one container.
Overview
Project status, recent activity, and key actions appear here.
JTabbedPane tabs = new JTabbedPane();
tabs.addTab("Home", homePanel);
tabs.addTab("Settings", settingsPanel);
tabs.addTab("Help", helpPanel);
Experiment L — MDI workspace
Open, minimize, maximize, or close simulated internal windows. This illustrates the role of JDesktopPane and JInternalFrame.
Workspace ready. Create a window.
JDesktopPane desktop = new JDesktopPane();
JInternalFrame frame = new JInternalFrame(
"Inventory", true, true, true, true);
desktop.add(frame);
frame.setVisible(true);
Constructor flags are: resizable, closable, maximizable, iconifiable—in that order.
Experiment M — BoxLayout
Switch between vertical and horizontal arrangement. The browser demo illustrates the layout concept.
Save
Edit
Export
panel.setLayout(new BoxLayout(
panel, BoxLayout.Y_AXIS));
panel.add(new JButton("Save"));
panel.add(new JButton("Edit"));
Which component fits?
Choose a user requirement and match it to a Swing component.
Your match will appear here.
Accuracy note: the lecture introduces Swing APIs. In current industry work, Java Swing remains relevant in existing desktop/enterprise tools, while many new user-facing products may choose web, JavaFX, or other UI frameworks depending on requirements. The right choice depends on deployment, maintenance, accessibility, and team constraints.
Retrieval practice
Knowledge check
Answer each question, then check feedback. The goal is to explain why an approach fits—not just memorize a definition.
0 / 8 answered
About browser inspection tools
This page cannot reliably prevent browser Developer Tools, View Source, or inspection of downloaded HTML and JavaScript. Browser-side code is delivered to the visitor's device, so determined users can inspect or modify it. Avoid putting secrets, credentials, or sensitive data in this file. For protected data or graded assessments, use server-side validation and authorization.