CIS 1100 JavaDocs

Welcome to CIS 1100’s JavaDocs! This will serve as a means to document what functions are fair game for student usage to better assist with homework and exam prep. As always, please direct all questions to Ed and/or Office Hours!

Notes before reading the docs:

Functions are the ones that end with parentheses (), while static values such as Integer.MAX_VALUE, Math.PI etc. are constants with some value.
All headers have a JavaDocs reference link if anyone wants to explore more. They will have more functions and values, but we have this doc to highlight the most common ones used in this class.
Files In.java and PennDraw.java have their own reference pages linked in the headers.
Each function call / value has a description with some examples of usage and common errors. They are not exhaustive but just highlight common usecases.

Double

public static double MAX_VALUE;

Definition: Maximum value a double can store

Use Case:

double x = Double.MAX_VALUE;
double y = Double.max_value; // Error (it's case sensitive)

public static double MIN_VALUE;

Definition: Minimum value a double can store

Use Case:

double x = Double.MIN_VALUE;
double y = Double.min_value; // Error (it's case sensitive)

public static double POSITIVE_INFINITY;

Definition: Representation of positive infinity (\(\infty\)) in Java

Use Case:

double x = Double.POSITIVE_INFINITY;
double y = Double.positive_infinity; // Error (case sensitive)

public static double NEGATIVE_INFINITY;

Definition: Representation of negative infinity (\(-\infty\)) in Java

Use Case:

double x = Double.NEGATIVE_INFINITY;
double y = Double.negative_infinity; // Error (case sensitive)

public double parseDouble() {...}

Definition: parseDouble() reads a string and returns a number if it contains one, else throws a NumberFormatException if string has no number, or NullPointerException if the string is null

Use Case:

double x = Double.parseDouble("1100"); // returns 1100.0
double y = Double.parseDouble("cis1100"); // NumberFormatException
String s; // s is null
double z = Double.parseDouble(s); // NullPointerException

Integer

public int parseInt() {...}

Definition: parseInt() reads a String and returns a number if it contains one, else throws a NumberFormatException

Use Case:

int x = Integer.parseInt("-1100"); // returns -1100
int y = Integer.parseInt("cis1100"); // NumberFormatException
String s; // s is null
int y = Integer.parseInt(s); // NumberFormatException
// (NOT a NullPointerException as seen in Double.parseDouble() with a null string)

public static int MAX_VALUE;

Definition: Maximum value an int can store (\(2^{31} - 1\))

Use Case:

int x = Integer.MAX_VALUE;
int y = Integer.max_value; // Error (it's case sensitive)

public static int MIN_VALUE;

Definiton: Minimum value an int can store (\(-2^{31}\))

Use Case:

int x = Integer.MIN_VALUE;
int y = Integer.min_value; // Error (it's case sensitive)

Math

public static double abs(double/int a) {...}

Definition: Takes in a double or int as argument, and returns absolute value of respective type

Use Case:

double x = Math.abs(-3); // returns 3
double y = Math.abs(-245.34); // returns 245.34
int x = Math.abs(-2.3); // Error (type mismatch)

public static double ceil(double a) {...}

Definition: Returns the smallest double value \(\geq a\) which is an integer

Use Case:

double x = Math.ceil(-5.5); // returns -5.0
double y = Math.ceil(3.2); // returns 4.0
double z = Math.ceil(2); // returns 2.0
int p = Math.ceil(2.4); // Error (assigning double to int)

public static double floor(double a) {...}

Definition: Returns the largest double value \(\leq a\) which is an integer

Use Case:

double x = Math.floor(-5.5); // returns -6.0
double y = Math.floor(3.2); // returns 3.0
double z = Math.floor(2); // returns 2.0
int p = Math.floor(2.4); // Error (assigning double to int)

public static double max(double/int a, double/int b) {...}

Definition: Returns the larger of 2 values. (In case of doubles, +0 > -0)

Use Case:

double a = 7;
double b = 3;
double maxVal = Math.max(a, b); // returns 7

public static double min(double/int a, double/int b) {...}

Definition: Returns the smaller of 2 values. (In case of doubles, -0 < +0)

Use Case:

double a = 7;
double b = 3;
double minVal = Math.min(a, b); // returns 3

public static double random() {...}

Definition: Generates a pseudo-random double [0, 1) (1 isn’t a possible result, 0 is).

Change Possible Values

Let’s say we wanted to generate \([3,\ldots,6]\) inclusive, as integers, we would do the following:

int x = (int) (3 + Math.random() * 4)

More generally for range \([\texttt{low},\ldots,\texttt{high}]\):

int range = low + (int) (Math.random() * (high - low + 1))

Other Use Cases:

double x = Math.random(); // can store in variable
if (Math.random() > 0.5) { ... } // or, can call it directly

boolean b = Math.random() < 1; // ALWAYS true

public static double PI;

Definition: Stores the value of \(\pi\)

Use Case:

double pi = Math.PI;
double x = Math.pi; // Error (case sensitive)

public static double pow(double base, double exponent) {...}

Definition: Returns \(\texttt{base}^{\texttt{exponent}}\).

Note Inefficiency - squaring and cubing should instead be \(x * x\) and \(x * x * x\), as Math.pow() is inefficient for low powers.

Use Case:

double x = Math.pow(-3, 3); // returns -27.0
double y = Math.pow(2, 2); // returns 4.0
double z = Math.pow(4, -1); // returns 0.25

public static double sqrt(double a) {...}

Definition: Returns \(\sqrt a\)

Note: Math.sqrt() of a negative number just gives you NaN (Not a Number).

Use Case:

double x = Math.sqrt(25); // returns 5.0
double y = Math.sqrt(2); // returns 1.4142135623730951
double z = Math.sqrt(-4); // returns NaN

String

public char charAt(int index) {...}

Definition: charAt returns the character at the specified index of the Stringvariable. Make sure the index is within the bounds of the String!

Use Case:

String s = "CIS1100";
s.charAt(0); // returns 'C'
s.charAt(7); // throws IndexOutOfBoundsException

public boolean equals(Object anObject) {...}

Definition: equals will compare the String with another String passed into the function and check for equality. Make sure to use .equals() rather than comparing two strings with ==.

Use Case:

String s = "CIS1100";
s.equals("CIS1100"); // returns true
s.equals("CIS1200"); // returns false

public int indexOf(int ch) {...}

Definition: indexOf will return the first index that the character (represented as an integer) ch appears at in the String. If the character does not appear in the String, then indexOf returns -1.

Use Case:

String s = "CIS1100";
s.indexOf('C'); // returns 0
s.indexOf('2'); // returns -1

public int length() {...}

Definition: length returns the length of this String.

Use Case:

String s = "CIS1100";
s.length(); // returns 7

public String substring(int beginIndex) {...}

Definition: substring(int beginIndex) will return a substring of this String that begins at the index beginIndex and ends at the end of the String. substring() is overloaded.

public String substring(int beginIndex, int endIndex) {...}

Definition: substring(int beginIndex, int endIndex) returns a substring of this String that begins at the index beginIndex and ends at the index endIndex - 1 inclusive (that is, endIndex is not included).

In both cases, if beginIndex or endIndex are out of bounds of the String’s length, or if beginIndex > endIndex, substring() will throw an IndexOutOfBoundsException.

Use Case:

String s = "CIS1100";
s.substring(3);     // returns "1100"
s.substring(2, 5);  // returns "S11"
s.substring(-4);    // throws IndexOutOfBoundsException
s.substring(2, 10); // throws IndexOutOfBoundsException
s.substring(5, 2);  // throws IndexOutOfBoundsException

public String toLowerCase() {...}

Definition: toLowerCase() converts all the characters in the String to lowercase characters. Doesn’t change non-letter characters, such as numbers and punctuation.

Use Case:

String s = "CIS1100";
s.toLowerCase(); // returns "cis1100"
System.out.println(s) // prints "CIS1100" becuase strings are immutable
s = s.toLowerCase();
System.out.println(s); // now prints "cis1100"

public String toUpperCase() {...}

Definition: toUpperCase() converts all the characters in the String to uppercase characters. Again, doesn’t change non-letter characters, such as numbers and punctuation.

Use Case:

String s = "cis1100";
s.toUpperCase(); // returns "CIS1100"
System.out.println(s) // prints "cis1100" becuase strings are immutable
s = s.toUpperCase();
System.out.println(s); // now prints "CIS1100"