Simple File Encryption in Java: Explanation & Practice

Encrypt file contents using Caesar cipher

Problem summary

Read a file, encrypt using Caesar cipher (shift each letter by 3), write to output.

Starter code

import java.io.*;

public class Main {
    public static void main(String[] args) {
        int shift = 3;
        // Read input.txt
        // Encrypt with Caesar cipher
        // Write to encrypted.txt
        // Print: Encryption complete
    }
}

Expected output and test cases

File encrypted
```
Encryption complete
```
Simple shift
```
ABC -> DEF
```
Wrap around
```
XYZ -> ABC
```

Hints

Handle uppercase and lowercase separately
Wrap around at Z/z
Non-letters stay unchanged

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