File Class

The File class in Java (from the java.io package) represents a file or directory path in the file system. It is used to create, delete, inspect, and manage files/directories, but does not read or write file content. This is a high-frequency interview topic, often confused with file I/O streams.

What Is the File Class?

• Represents file or directory metadata
• Works with paths, not content
• Platform-independent (uses OS-specific separators internally)
• Part of java.io package

File file = new File("data.txt");
          

What File Can and Cannot Do

✔ Can Do

• Check existence
• Create/delete files & directories
• Get file properties (name, size, path, permissions)
• List directory contents

❌ Cannot Do

• Read file data
• Write file data

(Use streams/readers/writers for content I/O)

Creating a File Object

1️⃣ Using Relative Path

File f = new File("data.txt");
          

✔ Path relative to current working directory

2️⃣ Using Absolute Path

File f = new File("C:\\files\\data.txt");
          

3️⃣ Using Parent + Child

File f = new File("C:\\files", "data.txt");
          

✔ Cleaner and safer path handling

Commonly Used Methods (Must-Know)

Existence & Type Checks

f.exists();        // true/false
f.isFile();        // file?
f.isDirectory();   // directory?
          

File Information

f.getName();
f.getPath();
f.getAbsolutePath();
f.length();        // size in bytes
f.lastModified();
          

Permissions

f.canRead();
f.canWrite();
f.canExecute();
          

Creating Files and Directories

Create a File

File f = new File("test.txt");
f.createNewFile();   // throws IOException
          

✔ Creates empty file if not exists

❌ Returns false if already exists

Create Directory

File dir = new File("logs");
dir.mkdir();        // single directory
          

Create Directory Tree

File dir = new File("a/b/c");
dir.mkdirs();       // creates parent directories too
          

Deleting Files and Directories

f.delete();
          

⚠ Directory must be empty to delete successfully

Listing Directory Contents

List Names

File dir = new File("C:\\files");
String[] names = dir.list();
          

List Files as File Objects (Preferred)

File[] files = dir.listFiles();
          

✔ Allows further inspection

Renaming / Moving Files

File oldFile = new File("old.txt");
File newFile = new File("new.txt");
oldFile.renameTo(newFile);
          

✔ Also works as move if paths differ

⚠ Behavior may vary across OS

File Separator (Platform-Independent)

File.separator
          

✔ Avoid hardcoding / or \\

File vs Streams (Interview Trap)

File vs Path (Modern Java)

✔ Use Path + Files for new code

✔ Still must know File for interviews

Common Beginner Mistakes

• Assuming File reads/writes content
• Forgetting createNewFile() throws exception
• Deleting non-empty directories
• Hardcoding path separators
• Ignoring return values of mkdir() / delete()

Interview-Ready Answers

Short Answer

The File class represents a file or directory path in Java.

Detailed Answer

In Java, the File class from the java.io package is used to represent file and directory paths. It provides methods to create, delete, and inspect files and directories, but it does not perform actual file reading or writing. For content I/O, streams or NIO APIs are used.

Key Takeaway

File is about paths and metadata, not data.

Use it to manage files and directories, and combine it with streams or NIO for actual I/O operations.