Java classes that model real app data

Turn a note into a small, immutable data model with a clear public interface.

1. Model a note

public final class Note {
    private final String title;

    public Note(String title) {
        if (title == null) throw new IllegalArgumentException("title is required");
        this.title = title;
    }

    public String getTitle() { return title; }
}

2. Construct an instance

Note note = new Note("Learn Android");
System.out.println(note.getTitle());

Private state and a small public interface make an object easier to reason about. A final class prevents subclassing; a final field cannot be reassigned after initialization. This works well here because String is immutable too.

Expected output

The Java program prints Learn Android. Creating a note with null throws the explicit validation error.

Troubleshooting

Put the public class in Note.java. A constructor has no return type and must have the same name as its class.

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