A package in Java is used to organize related classes, interfaces, and other types. Packages help organize large programs, avoid naming conflicts, and control access.
A package groups related Java classes and interfaces under a common name.
For example, a school management application might contain:
student package for student-related classes.teacher package for teacher-related classes.fees package for fee management.package student;
public class Student {
public void display() {
System.out.println("Student details");
}
}The package declaration identifies the package to which the class belongs.
| Type | Description | Examples |
|---|---|---|
| Built-in packages | Provided by the Java platform. | java.util, java.io |
| User-defined packages | Created by developers to organize application code. | student, school |
Create a Java file named Student.java
inside a folder named student.
File: student/Student.java
package student;
public class Student {
public void show() {
System.out.println("Welcome to Java Packages");
}
}The package declaration must appear before the class declaration, except for comments and annotations allowed before it.
Example folder structure:
MyProject/
└── student/
└── Student.javaYou can import a public class from another package and create its object.
File: student/Student.java
package student;
public class Student {
public void show() {
System.out.println("Student class called");
}
}File: Main.java
import student.Student;
class Main {
public static void main(String[] args) {
Student s1 = new Student();
s1.show();
}
}Student class calledThe Main class imports Student using its package name and then creates an object.
The import keyword allows you to refer
to accessible types by their simple names rather
than writing their fully qualified names each time.
import java.util.Scanner;
class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.print("Enter your name: ");
String name = sc.nextLine();
System.out.println("Hello " + name);
sc.close();
}
}Enter your name: Rahul
Hello Rahul
Here, Scanner belongs to the
java.util package.
You can import multiple classes from the same package using separate import statements.
import java.util.Scanner;
import java.util.ArrayList;
class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
ArrayList names = new ArrayList<>();
names.add("Rahul");
names.add("Priya");
System.out.println(names);
sc.close();
}
} [Rahul, Priya]
Both Scanner and ArrayList are in the
java.util package.
You can use a wildcard import to make accessible types in a package available by their simple names.
import java.util.*;
class Main {
public static void main(String[] args) {
ArrayList fruits = new ArrayList<>();
fruits.add("Apple");
fruits.add("Mango");
fruits.add("Banana");
System.out.println(fruits);
}
} [Apple, Mango, Banana]
The * wildcard imports accessible
types declared in that package. It does not
automatically import classes from its subpackages.
| Package | Purpose | Common Types |
|---|---|---|
java.lang |
Core language classes. | String, Math, System |
java.util |
Collections and utilities. | Scanner, ArrayList, HashMap |
java.io |
Traditional input/output. | File, FileReader, BufferedReader |
java.nio.file |
Modern file and path operations. | Path, Files |
java.time |
Date and time operations. | LocalDate, LocalTime |
java.net |
Networking. | URL, Socket |
java.lang are automatically
available by simple name in ordinary Java source
files. Other packages generally need imports or
fully qualified names.
A fully qualified class name includes the package name followed by the class name. You can use it without an import statement.
class Main {
public static void main(String[] args) {
java.util.ArrayList names =
new java.util.ArrayList<>();
names.add("Rahul");
names.add("Amit");
System.out.println(names);
}
} [Rahul, Amit]
The fully qualified name is
java.util.ArrayList.
A project can contain multiple packages to organize its classes by responsibility.
SchoolProject/
├── Main.java
├── student/
│ └── Student.java
├── teacher/
│ └── Teacher.java
└── fees/
└── FeeManager.java
Each class can declare its corresponding package.
For example, Student.java begins with
package student;.
A typical source file places its package declaration first, followed by imports and then its type declarations.
Suppose your project contains these files:
MyProject/
├── Main.java
└── student/
└── Student.java
The Student.java file contains
package student;, and Main.java imports
student.Student.
Step 1: Open a terminal in MyProject.
Step 2: Compile both source files.
javac -d . Main.java student/Student.java
The -d . option tells the compiler
to place generated class files in the current
directory structure according to their packages.
Step 3: Run the Main class.
java MainStudent class calledImporting a class does not grant additional access to private or package-private members. Access still depends on Java's access rules.
student
and add a Student class with a display() method.
java.util to accept a student's name.
java.util
to store five student names.
java.time.LocalDate.
student and
teacher packages in one project.
1. Which keyword declares a package in Java?
2. Which package contains the Scanner class?
3. What does the import keyword help you do?