Lesson 3-1: Java Basics 2

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Whitespace:

• Whitespace contains blanks, tabs, and newline characters

• Seperates individual words and symbols

• There will always be whitespace

• Whitespace makes code cleaner/easier to read

Errors:

• Syntax are the rules of a coding language that must be followed

• Semantics represent the meaning of the code

• Three types of errors:

  • Complier errors:

    • Will stop compiliation

    • Typically are syntax errors

  • Runtime errors:

    • Terminates the program when trying to run

    • Stack Trace: error message that contains statements/methods that were active when the error occured

    • Typically a semantics error

  • Logical errors:

    • Will continue to run, but incorrectly

    • Caused due to a semantic error

    • Usually no error messages

• Debugging is to find and fix errors in a program

Comments:

• Java contains three types of comments

• Line comments:

  • Is a single line
  • Starts with //

//This is a comment

• Block comments:

  • Can span multiple lines

/*
* Line 1
* Line 2
*/

• Javadoc comments:

  • Used by a tool called javadoc
  • Auto creates formatted html files with code description

/**
* Line 1
* Line 2
**/

Variables and Constants:

• Place in memory that stores a value/data

• Use camel casing when naming

  • Ex. itemCost

• Assign variables using the ’=’ operator

  • Can create and assign variables in the same line

• Variables have scope, which represents where it can be accesed in a program

  • A method can’t see variables delcared inside of another

• To make a variable a constant, add the keyword final before the variable type:

  • This makes the value of the variable unmodifiable

final int myNum = 59;

Primitive Types:

• List of all primitive types:

  • Integer based values:

• Byte (8-bits): Stores whole numbers from -128 to 127

• Short (16-bits): Stores whole numbers from -32,768 to 32,767

• Int (32-bits): Stores whole numbers from -2,147,483,648 to 2,147,483,647

• Long (64-bits): Stores whole numbers from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

  • Real number values (floating point):

• Float (32-bits): Stores fractional numbers with 6 to 7 decimals

• Double (64-bits): Stores fractional numbers with 15 to 16 decimals

  • Logical values:

• Boolean: Stores true/false

  • individual values:

• Char: Stores a single character

Default Types (Numerical Types):

• Values are given default types:

  • Number literal == int

  • Floating point == double

• You can append a special letter to a value to change its default type:

  • Long = 10L or 10l

  • Float = 10.0F or 10.0f

  • Double = 10D or 10d or 10.0

• Multiple type allow more control over the size of the data in a program

Char:

• Represents an individual character

• Characters don’t follow a sematically logical order (Ex. 1,2,3)

  • Due to this, character sets have been created

    • Java uses the UNICODE character set which includes:

      • Contains 65,536 characters

      • ACII (numbers, letters, punctuation, space, extra special characters)

      • Symbols and letters from other languages

• To assign a char, use single quotes ”:

char let = 'B';

Escape Sequences:

• Used to assign values such as ’ or ”

• Always contains two characters:

  • The first is always the ""

  • The second is the actual character

char quote = '\'';
char tab = '\t';
char newLine = '\n';
char carrigeReturn = '\r';
char backslash = '\\';
char doubleQuote = '\"';

Boolean:

• Can only show true/false

boolean yes = true;
boolean no = false;

Arithmetic Expressions and Operators:

• Math equations

• Must only return one value

• Arithmetic operators:

  • All are binary operators (Can be applied to two numbers)

  • Addition == ’+’

  • Subtraction == ’-’

  • Multiplication == ’*’

  • Division == ’/’

  • Remainder/Modulus == ’%’