AP CSA Full Review of Units 1-10 (2025)

Unit 1: Primitive Types

Note: variable long doesn’t show up in the exam

Casting

Unit 2: Using Objects

What are Objects and Classes

String Methods

Strings are not primitive types, but are composed of characters (char), which is a primitive type.

Essential Methods for the AP Exam
- int length()int length(): Returns the total number of characters in the string.
- String substring(int from, int to)String substring(int from, int to): Returns a new string starting at index from and ending just before index to (index to is exclusive). Length of result is (to−from)(to−from).
- String substring(int from)String substring(int from): Returns a new string starting at index from and going to the end of the string.
- int indexOf(String str)int indexOf(String str): Returns the index of the first occurrence of str within the string; returns −1−1 if not found.
- boolean equals(String other)boolean equals(String other): Checks if two strings contain the same characters in the same order.
- int compareTo(String other)int compareTo(String other): Compares strings lexicographically (alphabetically). Returns 00 if they are equal, a negative integer if the string is less than other, and a positive integer if it is greater.
Important Rules to Know
- Indexing: Java strings use zero-based indexing. The first character is at index 00, and the last character is at index length()−1length()−1.
- Bounds: Accessing an index less than 00 or greater than or equal to length()length() will throw a StringIndexOutOfBoundsException.
- Concatenation: You can use the ++ operator to join strings or a string and a primitive (the primitive will be converted to a string).

Wrapper Class

Math Class

The Math class provides static methods for common mathematical calculations. Since these are static, you call them directly using the class name.

static int abs(int x)static int abs(int x) / static double abs(double x)static double abs(double x): Returns the absolute value of a number (e.g., Math.abs(−5)Math.abs(−5) is 55).
static double pow(double base, double exponent)static double pow(double base, double exponent): Raises a base to a specific exponent. Crucially, this always returns a doubledouble.
static double random()static double random(): Returns a random doubledouble in the range [0.0,1.0)[0.0,1.0). To generate a random integer between minmin and maxmax, use: (int)(Math.random()∗(max−min+1))+min(int)(Math.random()∗(max−min+1))+min.
static double sqrt(double x)static double sqrt(double x): Returns the positive square root of a double value.
static int max(int a, int b)static int max(int a, int b) / static int min(int a, int b)static int min(int a, int b): Returns the larger or smaller of two values. Example: if a=10a=10