AP CSA Unit 1

Chapter 5: Introduction to Java

• Java Overview: Java is a high-level, object-oriented programming language. It is widely used for building cross-platform applications.

• Basic Structure of a Java Program:

  • Every Java program begins with a class.

  • A main method (public static void main(String[] args)) is the entry point of the program.

• Syntax and Semantics: Java code must follow strict rules (syntax) to run correctly. Semantics refers to the meaning behind the syntax.

• Compilation: Java code is first compiled into bytecode by the Java compiler. This bytecode is then executed by the Java Virtual Machine (JVM).

Chapter 6: Small Java Programs

• Writing Simple Programs: Programs can consist of simple tasks like printing messages or performing calculations.

  • Example:

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    public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, world!"); } }

• Syntax for Methods:

  • Methods in Java consist of a header (name, parameters, return type) and a body (the code to be executed).

  • Example:

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    public static void greet() { System.out.println("Welcome!"); }

• Comments: Java supports single-line (//) and multi-line (/* */) comments.

Chapter 7: How to Run the Example Programs

• Running Programs in an IDE or Terminal:

  • Use an Integrated Development Environment (IDE) like BlueJ, IntelliJ IDEA, or Eclipse to write, compile, and run Java programs.

  • Alternatively, you can use the command line to compile and run Java programs:

    • To compile: javac ProgramName.java

    • To run: java ProgramName

• Common Errors: Syntax errors (like missing semicolons) and runtime errors (such as dividing by zero) are common issues while running programs.

Chapter 8: Primitive Data

• Primitive Data Types:

  • int: Integer values (e.g., int age = 25;)

  • double: Floating-point numbers (e.g., double price = 19.99;)

  • boolean: True or false values (e.g., boolean isActive = true;)

  • char: Single characters (e.g., char grade = 'A';)

• Literals: The values assigned to variables (e.g., 25, 19.99, 'A').

• Arithmetic Operations: Basic math operations like +, -, *, /, and % (modulus).

• Type Casting: Converting one data type to another (e.g., casting a double to an int).

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  int num = (int) 4.99; // num becomes 4

Chapter 9: Variables and the Assignment Statement

• Variable Declaration: A variable must be declared with a type before it is used.

  • Example: int x;

• Assignment: After declaring a variable, you assign a value to it using the assignment operator =.

  • Example: x = 10;

• Constants: Declared with the final keyword. Constants cannot be changed after they are initialized.

  • Example: final int MAX_AGE = 100;

• Scope of Variables: The region in the code where a variable is accessible. Variables declared inside methods are local and can only be used within that method.

Chapter 10: Expressions and Arithmetic Operators

• Expressions: A combination of variables, literals, and operators that are evaluated to produce a value.

  • Example: int result = 3 + 4 * 2; (Java follows operator precedence).

• Arithmetic Operators:

  • + (addition)

  • - (subtraction)

  • * (multiplication)

  • / (division, returns quotient for integers)

  • % (modulus, returns the remainder)

• Increment/Decrement Operators:

  • ++: Increments a value by 1 (x++ or ++x).

  • --: Decrements a value by 1 (x-- or --x).

• Order of Operations: Follows PEMDAS (Parentheses, Exponents, Multiplication and Division, Addition and Subtraction).