Variables, Strings, and Debugging

24au ver.

Note: this is for the Autumn 2024 iteration of CSE 121. Looking for a different quarter? Please visit https://courses.cs.washington.edu/courses/cse121/.

Escape Sequences¶

Sequence	Description
`\t`	tab
`\n`	new line
`\"`	quotation mark
`\\`	backslash

Variables¶

containers (or boxes) that store values of a specific data type

Variable Creation	Code Framework	Description	Example
Declaration	`<type> <name>;`	creates a variable but doesn’t give it any value	`int x;`
Initialization	`<name> = <value>;`	stores a value into a variable	`x = 5;`
Declaration + Initialization	`<type> <name> = <value>;`	creates a variable and stores a value in it	`int x = 5;` `int x = 3;` (`x` has the value `3`) `int y = 1 + x * 2;` (`y` has the value `7`)

Variable Naming Rules & Conventions¶

Case-Sensitive
Starts with a letter, $, or _
Can have letters, numbers, $, or _
Generally, $, and _ are not used
Choose descriptive names
Use “camelCasing”

Examples:¶

age
dogName
numOfClasses

Strings¶

(Stores text)

Example

String name = "T. Swift";
System.out.println(name.length()); //string name has a length of 8

Indexing of String name:¶

char	T	.		S	w	i	f	t
index	0	1	2	3	4	5	6	7

String Methods¶

Method	Returns
`charAt(i)`	a character in this String at index `i`
`contains(str)`	`true` if this String contains `str` inside it, `false` otherwise
`endsWith(str)`, `startsWith(str)`	`true` if this String ends/starts with `str`, `false` otherwise
`equals(str)`	`true` if this String is the same as `str`, `false` otherwise
`equalsIgnoreCase(str)`	`true` if this String is the same as `str` ignoring capitalization, `false` otherwise
`indexOf(str)`	the index in this String where `str` begins, `-1` if not found
`length()`	the number of characters in this String
`replace(str, newStr)`	a new String with all `str` in this String replaced with `newStr`
`substring(i)`	characters in this String from index `i` (inclusive) to end (exclusive)
`substring(i, j)`	characters in this String from index `i` (inclusive) to `j` (exclusive)
`toLowerCase()`, `toUpperCase()`	a new String of this String with all lowercased or uppercased characters

Type Casting¶

(Assigning a value of one type to another data type)

Type Casting Framework¶

<type1> <name> = (<type2>) <value>;

double num = 5.2;
int myInt1 = num; // Compiler error. Incompatible types: possible lossy conversion from double to int
int myInt2 = (int) num; // Resolve incompatible types with casting; myInt2 has the value 5