COMP 250 Midterm 1 Crib Sheet

Cheat Sheet > COMP 250 Midterm 1 Crib Sheet

McGill University COMP 250 Java Syntax Reminders - Java is compiled and interpreted: Java source code → compiler → bytecode → interpreter (JVM) → output - Have to typecast when converting integers into chars → Ex: char first = ‘a’; char second = (char) (first + 1); - When converting to an integer, rounding will always go towar ...[Show More]

McGill University
COMP 250
Java Syntax

Reminders

- Java is compiled and interpreted: Java source code → compiler → bytecode → interpreter (JVM) → output

- Have to typecast when converting integers into chars → Ex: char first = ‘a’; char second = (char) (first + 1);

- When converting to an integer, rounding will always go towards zero

- To convert an int/double to a String, just concatenate the number with an empty string → ex: String s = “” + 4;

- To convert from a String to an int/double, use Integer.parseInt()/Double.parseDouble() → int x = Integer.parseInt(“54”);

- Doubles are approximate and should not be compared using == → instead do Math.abs(x - y) < 0.01

- When making 2D arrays, numbering is as follows → ex: new int[3][2] = {{0, 0}, {0, 0}, {0, 0}}

- If you don’t specify the length of the inner lists, you will get a list of null values → ex: new int[3][ ] = {null, null, null}

- Enhanced for loop: int[ ] numbers = {1, 2, 3, 4, 5}; for (int element: numbers) { System.out.println(element); }

- Default value for booleans is false

Order of operations:

1. Parentheses

2. Not (!)

3. Typecasting

4. Arithmetic → mult/div first, then add/subtract

5. Comparison → >, <, ≤, ≥ first, then ==, !=

6. Boolean → &&, ||

Errors/exceptions

- Compile-time errors → syntax errors which cause the code to not compile (ex: missing semicolon)

- Run-time errors → code doesn’t run (an exception is raised)

- Throwing: throw new ExceptionName(“message”) → message is optional

- Examples of exceptions: ArrayIndexOutOfBoundsException, IllegalArgumentException, NegativeArraySizeException

- Try/Catch blocks can catch specific exceptions using their names, or all exceptions using Exception

- Ex: try { // code } catch(Exception e) { // code to run if exception occurs }

- e.printStackTrace(): prints the info about the exception that occurred in your catch block

- Can also just print the name of the exception using print → ex: System.out.println(e)

- When a try block is in your program, you can use a finally block, which will always execute no matter what (even if there is

a return statement in the try/catch blocks)