Java Programming Labs

Your Task: Create a Drawable interface and implement it in Circle and Rectangle classes to demonstrate abstraction and polymorphism.

Detailed Requirements:
1. Create interface "Drawable" with two abstract methods:
   � void draw(); - prints shape being drawn
   � double getArea(); - returns calculated area

2. Create class "Circle" implementing Drawable:
   � Field: double radius
   � Constructor taking radius
   � Implement draw() to print "Drawing Circle"
   � Implement getArea() returning Math.PI * radius * radius

3. Create class "Rectangle" implementing Drawable:
   � Fields: double width, height
   � Implement both interface methods

4. Demonstrate polymorphism using Drawable array/references.

Interface Concepts:
� Interface = contract (what methods a class MUST have)
� implements keyword to use interface
� All interface methods are implicitly public abstract
� A class can implement multiple interfaces

Expected Output:
Drawing Circle with radius 5.0 Area: 78.54 Drawing Rectangle 4.0 x 6.0 Area: 24.0

Your Task: Write data to a file and read it back using Java's I/O classes with proper exception handling and resource management.

Detailed Requirements:
1. Import required classes:
   import java.io.*; (FileWriter, BufferedReader, FileReader, IOException)

2. Write to file using FileWriter:
   � Use try-with-resources: try (FileWriter writer = new FileWriter("data.txt")) { }
   � Write multiple lines using writer.write()

3. Read from file using BufferedReader:
   � try (BufferedReader reader = new BufferedReader(new FileReader("data.txt"))) { }
   � Read line by line with reader.readLine()

4. Handle IOException with catch block.

Key Concepts:
� try-with-resources - automatically closes file (Java 7+)
� FileWriter - writes characters to file
� BufferedReader - efficient reading with buffer
� Always handle IOException for file operations

Expected Output:
Writing to file... File written successfully! Reading from file: Line 1: Hello, Java! Line 2: File I/O is easy. Line 3: Keep learning!

Your Task: Master essential String methods by processing and transforming text data using Java's built-in String methods.

Detailed Requirements:
1. Basic String operations:
   � length() - get string length
   � toUpperCase() / toLowerCase() - change case
   � trim() - remove leading/trailing whitespace

2. Searching and extracting:
   � charAt(index) - get character at position
   � indexOf("text") - find position of substring
   � substring(start, end) - extract portion

3. Comparison and checking:
   � equals() - compare strings (NOT ==)
   � contains() - check if contains substring
   � startsWith() / endsWith()

4. Transformation:
   � replace(old, new) - replace occurrences
   � split(delimiter) - split into array

Expected Output:
Original: " Hello, Java World! " Trimmed: "Hello, Java World!" Length: 18 Uppercase: "HELLO, JAVA WORLD!" Contains "Java": true Index of "World": 12 Substring(7,11): "Java" Replace: "Hello, Python World!" Split by comma: ["Hello", " Java World!"]