Quiz: Java Basics

Notes.txt

Non-numerical math values in java:
  n/0.0 = Infinity where n is a positive number
  n/0.0 = -Infinity where n is a negative number 
  0/0.0 = NaN (can also do 0.0/0.0)
  note the 0.0 is a decimal and not an integer

Operators:
  + adds the numbers
  - subtracts the numbers
  * multiplies the numbers
  / divides the numbers (if both numbers used are both integers, drop the decimal once done dividing)
  % divides the numbers and returns the remainder

BEDMAS:
  You should know these but here they are
  B - brackets
  E - exponents
  D - division
  M - multiplication
  A - addition
  S - subtraction
  
  division and multiplication can be switched around
  addition and subtraction can be switched around
  

Math Class:

  double Math.E() returns Euler's number (e)
  double Math.PI() returns PI

  t Math.abs(n) returns the absolute value of n with the same type specified in the paramater (int/long/float/double)
  double Math.pow(n1, n2) returns n1 raised to the power of n2 
  double Math.random() returns a random number between 0 and 1 (0 inclided 1 is not)
  double Math.sqrt(n) returns the square root of n
  double Math.exp(n) returns e to the power n
  double Math.log(n) returns the logarithm of n to base e
  double Math.log10(n) returns the logarithm of n to base 10
  double Math.sin(n) returns the sine of n
  double Math.cos(n) returns the cosine of n
  double Math.tan(n) returns the tangent of n
  double Math.toRadians(n) returns n (angle in degrees) converted to radians
  double Math.toDegrees(n) returns n (angle in radians) converted to degrees
  t Math.max(n, m) returns the larger value of n and m with the same type specified in the paramater (int/long/float/double)
  t Math.min(n, m) returns the smaller value of n and m with the same type specified in the paramater (int/long/float/double)
  double Math.floor(n) Returns the closest integer-valued double which is equal to or less than n
  double Math.ceil(n) Returns the closest integer-valued double which is equal to or greater than n
  double Math.rint(n) Returns the closest integer-valued double to n
  long Math.round(n) Returns the long which is closest in value to the double n
  int Math.round(n) Returns the int which is closest in value to the float n

Naming conventions:
  1) under 256 characters
  2) only letters, digits and underscores (_)
  3) can’t start with a digit
  4) no spaces
  5) no reserved keywords


Most of these are based off memory so there might be some slight inaccuracy, others were found through googling

Note that most of these you won't need to know their use, just need to know the keywords
Reserved keywords:

  Data types:
    boolean - stores true or false
    byte - stores whole numbers from -128 to 127
    char - stores a single character/ASCII values
    int - stores whole numbers from -2,147,483,648 to 2,147,483,647
    long - stores whole numbers from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
    short - stores whole numbers from -32,768 to 32,767
    float - stores fractional numbers, sufficient for storing 6 to 7 decimal digits
    double - stores fractional numbers, sufficient for storing 15 decimal digits

  Access Control:
    private - can only be accessed in the class
    protected - can only be accessed in the class or a subclass
    public - can be accessed anywhere

  Modifiers:
    abstract -  a non-access modifier, used for classes and methods
    final - a non-access modifier used for classes, attributes and methods (not changeable)
    finally - executes no matter if the try-except failed or passed
    native - specifies that a method is not implemented in the same java source file
    private - can only be accessed in the class
    protected - can only be accessed in the class or a subclass
    public - can be accessed anywhere
    static - is a non-access modifier used for methods and attributes
    transient - specifies that an attribute is not part of an object's persistent state
    synchronized - specifies that methods can only be accessed by one thread at a time
    volatile - attribute is not cached thread-locally
    strictfp - restrict the precision and rounding of floating-point calculations

  Catch-Exception:
    try - tries to execute some code
    catch - catches the exception raised in try (if applicable)
    finally - executes no matter if the try-except failed or passed
    throw - throw an error
    throws - what error may be thrown

  Loops or decision-makes:
    break - exits the loop
    case - used in a switch-case statement to specify a case
    continue - stops the current iteration of the loop and moves on to the next
    default - the default block of code in a switch statement, if it's the last statement, it doesn't need a break
    do - used together with while to create a do-while loop (please don't do this, just make a while loop normally)
    while - similar to if, however, continually executes the code until the boolean is false
    for - can be used to perform a task a specific number of times or be used to loop through an array (in python we say list instead of list)
    switch - the expression is compared with the values of each case, if none match, then the default is used, if there isn't a default, nothing happens
    if - used to check a condition, if true execute the code once
    else - if the condition in the if statement is false, the code is executed

  Class functions:
    abstract - a non-access modifier, used for classes and methods
    assert - for debugging
    class - used to create a class
    extends - extends a class (indicates that a class is inherited from another class)
    enum - declares an enumerated type
    implements - is used to implement an interface
    import - used to import a package, class or interface
    instanceof - checks whether an object is an instance of a specific class or an interface
    new - creates new objects
    package - creates a package
    return - what a function returns
    interface - used to declare a special type of class that only contains abstract methods
    this - the way you reference the class object
    throws - what error may be thrown
    void - specifies that a method should not have a return value
    super - refers to superclass (parent) objects

  Assigned values:
    true - self-explanatory
    false - self-explanatory
    null - self-explanatory

  Outdated keywords:
    const - use final instead 
    goto - not in use, and has no function

Casting: 
  Automatic type conversion can happen if both types are compatible and the target type is larger than the source type
  Example:
  	byte i = 50;
	  // No casting needed for below conversion
	  short j = i;
	  int k = j;
	  long l = k;
	  float m = l;
	  double n = m;
  
  It can also happen if a decimal value is added/subtracted/multiplied/divided to an integer value

  When you are assigning a larger type to a smaller type, then explicit casting is required
  Example:
    double d = 75.0;
		// Explicit casting is needed for below conversion
		float f = (float) d;
		long l = (long) f;
		int i  = (int) l;
		short s = (short) i;
		byte b = (byte) s;

  
		

Generating random numbers:
  (int) (Math.random() * ((max/increment) + 1)) * increment + min