Java Quick Reference
These are the library classes and methods that may appear on the AP Computer Science A Exam. You get this sheet on exam day, so focus on knowing how to use the methods rather than memorizing them.
String Class
String(String str)Constructs a new String object that represents the same sequence of characters as str
int length()Returns the number of characters in a String object
String substring(int from, int to)Returns the substring beginning at index from and ending at index to - 1
String substring(int from)Returns substring(from, length())
int indexOf(String str)Returns the index of the first occurrence of str; returns -1 if not found
boolean equals(Object other)Returns true if this corresponds to the same sequence of characters as other; returns false otherwise
int compareTo(String other)Returns a value < 0 if this is less than other; returns zero if this is equal to other; returns a value > 0 if this is greater than other. Strings are ordered based upon the alphabet.
String[] split(String del)Returns a String array where each element is a substring of this String, which has been split around matches of the given expression del
Integer Class
Integer.MIN_VALUEThe minimum value represented by an int or Integer
Integer.MAX_VALUEThe maximum value represented by an int or Integer
static int parseInt(String s)Returns the String argument as an int
Double Class
static double parseDouble(String s)Returns the String argument as a double
Math Class
static int abs(int x)Returns the absolute value of an int value
static double abs(double x)Returns the absolute value of a double value
static double pow(double base, double exponent)Returns the value of the first parameter raised to the power of the second parameter
static double sqrt(double x)Returns the nonnegative square root of a double value
static double random()Returns a double value greater than or equal to 0.0 and less than 1.0
ArrayList Class
int size()Returns the number of elements in the list
boolean add(E obj)Appends obj to end of list; returns true
void add(int index, E obj)Inserts obj at position index (0 <= index <= size), moving elements at position index and higher to the right (adds 1 to their indices) and adds 1 to size
E get(int index)Returns the element at position index in the list
E set(int index, E obj)Replaces the element at position index with obj; returns the element formerly at position index
E remove(int index)Removes element from position index, moving elements at position index + 1 and higher to the left (subtracts 1 from their indices) and subtracts 1 from size; returns the element formerly at position index
File Class
File(String pathname)The File constructor that accepts a String pathname
Scanner Class
Scanner(File f)The Scanner constructor that accepts a File for reading
int nextInt()Returns the next int read from the file or input source if available. If the next int does not exist or is out of range, it will result in an InputMismatchException.
double nextDouble()Returns the next double read from the file or input source. If the next double does not exist, it will result in an InputMismatchException.
boolean nextBoolean()Returns the next boolean read from the file or input source. If the next boolean does not exist, it will result in an InputMismatchException.
String nextLine()Returns the next line of text as a String read from the file or input source; can return the empty string if called immediately after another Scanner method that is reading from the file or input source
String next()Returns the next String read from the file or input source
boolean hasNext()Returns true if there is a next item to read in the file or input source; false otherwise
void close()Closes this scanner
Object Class
boolean equals(Object other)String toString()