AP CSA EXAM PREP

Introduction

• Host: Harley, a former computer science teacher with experience in teaching AP Computer Science A (AP CSA).
• Objective: Provide a comprehensive review of AP CSA material in one go, using a code editor for live examples.

Unit 1: Introduction to Java

• Hello World Example: First program usually taught.

• System.out.println vs. System.out.print:

  • println adds a new line after printing, while print does not.
  • Example: System.out.print("Hello"); System.out.print("World"); results in HelloWorld on the same line, whereas System.out.println will result in:
  • Hello
  • World

• Syntax Errors: Mistakes in the format/structure of code (e.g., typos).

• Logic Errors: Code runs but does not produce the expected result.

• Comments: Use // for single-line comments; /* ... */ for multi-line comments. Comments do not affect code execution.

• String Literal: Text enclosed in quotes.

• Main Method: public static void main(String[] args), the entry point of any Java application.

  • Code execution begins from the main method.

• Variables:

  • Three parts: type, name, value.
  • Example: int x = 5;
  • Must match variable type with assigned value (e.g., no int x = "5";).
  • Common variable types include: int, double, boolean, String.

Unit 2: Classes and Objects

• Classes and Objects: Classes define data types; objects are instances of classes.
• Attributes (instance variables) store object characteristics; methods define behaviors.
• Example of a class definition:

  public class Person {
      private String name;  
      private int age;  
      // Constructor  
      public Person(String name, int age) {
          this.name = name;
          this.age = age;
      }
      // Method  
      public void sayHi() {
          System.out.println("Hello, my name is " + name);
      }
  }

• Constructors: Initialize new objects and set initial attribute values.
• Accessing Attributes: Public variables can be accessed outside the class; private variables cannot.

Unit 3: If Statements

• If Statements: Control structures to execute code based on conditions.
  • Syntax:

  if (condition) {
      // code to execute if condition is true
  } else {
      // code to execute if condition is false
  }

• Boolean Expressions: == for equality, != for inequality.
• Common pitfalls include confusing single (=) and double (==) equals signs when comparing values.

Unit 4: Loops

• While Loop: Repeats code as long as a condition is true.
  • Syntax:

  while (condition) {
      // code
  }

• For Loop: Commonly used to iterate over an array or range.
  • Syntax:

  for (int i = 0; i < limit; i++) {
      // code
  }

• Nested loops are allowed, but avoid infinite loops by ensuring the loop condition eventually becomes false.

Unit 5: More on Classes

• Similar structure to Unit 2. Focus on writing methods and using getters and setters for private variables.
• Getters and Setters: Methods to retrieve and update private attributes.
  • Syntax example for getter:

  public String getName() {
      return name;
  }

Unit 6: Arrays

• Arrays: Fixed-size data structure to store multiple values of the same type.
  • Example: int[] scores = {90, 80, 70};
  • Access elements using index: scores[0] gives 90.
  • Length: scores.length gives the number of items in the array.

Unit 7: ArrayLists

• ArrayLists: Dynamic arrays that can grow in size.
  • Use ArrayList<Type> for declaration, add items using add(), access using get(index).
  • Syntax example:

  ArrayList<String> fruits = new ArrayList<>();
  fruits.add("Apple");

Unit 8: 2D Arrays

• 2D Arrays: Arrays of arrays. Typically used for matrices.
  • Example: int[][] matrix = {{1, 2}, {3, 4}};
  • Accessing: matrix[0][1] gives 2.

Unit 9: Inheritance

• Basic principle of inheritance in classes. Subclasses inherit attributes and methods from parent classes.
• Keywords: extends to denote inheritance.
• Example:

  public class Car extends Vehicle {
      // Car-specific properties and methods
  }

Unit 10: Recursion

• Recursion: Method calls itself to solve problems.
• Base case: Condition under which the recursion stops.
• Example: Calculating factorial using recursion.
  • factorial(n) calls factorial(n-1) until base case is reached.