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Packages

Packages in Java

A package is an encapsulation mechanism used to group related classes and interfaces into a single unit.

Examples

  • All database-related classes are grouped under java.sql.
  • All file I/O-related classes are grouped under java.io.
Screenshot demonstrating packages
Figure: package concept illustration

Advantages of Packages

  • Resolve name conflicts (unique identification).
  • Improve modularity and maintainability.
  • Provide security for components.
Use the reverse domain name convention for package names (e.g. com.example.project).
Small screenshot about javac
Figure: javac output example

Naming Convention — Example

com.icicibank.loan.housing.Account
  • com.icicibank — reversed domain
  • loan — module
  • housing — sub-module
  • Account — class
Package folder structure screenshot
Figure: package folder structure created with javac -d .

Example Program

package com.code.java;

public class Test {
    public static void main(String[] args) {
        System.out.print("hello");
    }
}

Compilation

Normal compilation:

javac Test.java

Using -d to generate package folders:

javac -d . Test.java
If the specified destination directory does not exist, compilation will fail with a "directory not found" error.
Final screenshot
Figure: additional screenshot

Important Rules / Conclusion

  • Only one package statement is allowed at the top of a source file.
  • The package statement (if present) must be the first non-comment line.
  • Valid file order: package → imports → class/interface/enum.

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