24su ver.
Note: this is for the Summer 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:¶
agedogNamenumOfClasses
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 = (double) num; // Resolve incompatible types with casting; myInt2 has the value 5