Packages

Packages

1. What Is a Package? (beginner)

Package = folder for classes (namespace!). Prevents name clash (com.college.Student vs com.bank.Student!), organizes code, controls access (default = package-only!). Like surname for classes!

2. Code — Create + Use (exam steps!)

// File: com/college/Student.java
package com.college; // FIRST line! (folder path!)
public class Student {
    public void hi() { System.out.println("hi college!"); }
}
// File: Main.java (anywhere, with classpath!)
import com.college.Student; // import (like address!)
public class Main {
    public static void main(String[] args) {
        Student s = new Student(); s.hi();
    }
}

Compile: javac -d . Student.java Main.java (-d builds folders!). Run: java Main.

3. Import Forms

Form	Meaning
import com.college.Student;	one class (preferred!)
import com.college.*;	all college classes
import static java.lang.Math.*;	statics w/o prefix (sqrt(16)!)
no import	java.lang (auto!) + same package (auto!)

4. Traps

• package FIRST line (before import! comments ok above).
• Class file must sit in matching folder (com/college/Student.class!).
• Default (no modifier) = package-private (other packages can't see!).

5. Exam Points

• Create + import program with commands — 5-7 marks, very frequent.
• Import forms + default access — 3 marks, frequent.