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Transcript

  • 1. Primitive Data Types
    • Represent single values
    • Practically unlimited access
    • Integers types:
      • 2010
      • -40
    • Floating point (decimals) numbers types:
      • Big integers
      • Decimals: 3.14159
      • Scientific notation: 6.03e23
    • Boolean type: true or false
    • Character type: ‘c’
    • Strings : “Vote for Pedro”
  • 2. Variables
    • To store or remember data Java uses variables .
    • Variables contain primitive values or object references.
    • To be used, variables have to be declared and set
    • Declaring a variable:
      • Announces is existence to the rest of the block
      • Sets aside a section of memory big enough to store the value
      • Determines what kind of value can be stored in the variable
      • Determines how the number is to be interpreted
  • 3. Variables
    • Variable names should be describe the value they hold
    • Names with multiple words:
      • Lower case first word, capitalize subsequent words
      • Separate words with underscore.
    • Declaring a variable:
      • Type name followed by the name and optional initialization
        • int studentAge = 18;
        • double pi = 3.14159;
        • boolean isValid = false;
        • char marks_the_spot = ‘x’;
        • String vote4 = “Pedro”;
  • 4. Variable Scope
    • Variables are known inside the block in which they are declared.
      • class Foo {
      • int x = 0;
      • void someMethod() {
      • int y;
      • y = x + 1;
      • }
      • void anotherMethod() {
      • x = y + 1;
      • }
      • }
  • 5. Integers
    • Integers are 32 bits long
    • -2,147,483,648 <= int <= 2,147,483,647
    • Example declarations and values
    • int m;
    • m = 0;
    • int n = 23;
    • int o = -40;
  • 6. Floating Point
    • The type is called double
    • 64 bits long
      • Some bits used for the exponent, some for the mantissa
    • +/- 1.7 x 10 ± 308 with 15 significant digits
    • double pi;
    • pi = 3.14159;
    • double x = 10.0;
    • double y = 6.02e23;
    • double z = -40;
  • 7. Boolean
    • A boolean value represents true or false
    • A boolean also can be used to represent any value with two states, such as a light bulb being on or off.
    • The reserved words true and false are the only valid values for a boolean type
    • boolean done = false;
    • boolean isMale = true;
  • 8. Characters
    • A char variable stores the numeric representation of a character
    • The Unicode character set lists the characters and their corresponding numeric representation
      • The Unicode character set uses sixteen bits per character, allowing for 65,536 unique symbols and characters from many world languages
    • Character literals are delimited by single quotes:
    • 'a' 'X' '7' '$' ',' ' ‘
    • char marksTheSpot = ‘X';
  • 9. Escape Sequences
    • The unicode set recognizes ‘characters’ that are not printable
    • These unprintable characters are referred to with escape sequences
    Escape Sequence  Unprintable character backspace tab newline carriage return
  • 10. Escape sequences
    • Printing unprintable characters moves the terminal window cursor
      • Printing a backspace character moves the cursor backwards on the same line
      • Printing a carriage return moves the cursor to the front of the current line
      • Printing a new line drops the cursor to the beginning of the next line
      • Print a tab moves the cursor to ahead to the next tab stop
  • 11. Escape sequences
    • Special characters must be escaped when using them as just a character
      • char singleQuote = ‘’’;
      • char doubleQuote = ‘”’;
      • char backslash = ‘;
    • In other words, the back-slash tells Java to ignore the normal meaning of the very next character
  • 12. Character Strings
    • A character string is a sequence of characters delimited by double-quotes:
      • “ To be, or not to be”
      • (Actually, character strings are not a primitive data type, but an object .)
      • String eagles;
      • eagles = “Hell, no!!”;
      • String ssn = “147431904”;
  • 13. Escape Sequences
    • What if we wanted to print a double quote character? System.out.println (&quot;I said &quot;Hello&quot;.&quot;);
    • An escape sequence is a series of characters that represents a special character
    • An escape sequence begins with a backslash character ( ), which indicates that the character(s) that follow should be treated in a special way:
    • System.out.println (&quot;I said &quot;Hello&quot;.&quot;);
  • 14. Constants
    • A constant is a variable that can only be assigned a value once.
    • The final modifier to declares a constant
      • final int MIN_HEIGHT = 60;
      • final int MAX_HEIGHT;
      • MAX_HEIGHT = 74;
    • Constants:
      • give names to otherwise unclear literal values
      • facilitate updates of values used throughout a program
      • prevent inadvertent attempts to change a value
  • 15. Assignment
    • An assignment statement changes the value of a variable
    • The assignment operator is the = sign
    total = 55;
    • The expression on the right is evaluated and the result is stored in the variable on the left
    • The value that was in total is overwritten (and lost)
    • You can only assign a value to a variable that is consistent with the variable's declared type
  • 16. Keyboard input
    • Reads typing from the console
      • Terminal window or DOS window
    • Based on the concept of the token
      • Tokens are string or printable characters separated by delimiters
      • E.g., “Vote for Pedro” has three tokens separated by a white-space delimiter.
      • E.g., “09/15/2010” has three tokens separated by a slash delimiter
  • 17. Reading Streams
    • The scanner object extracts tokens from the input stream.
    • Input stream can be the keyboard, a file, or a socket.
    • For example, creating the scanner
      • // Create a variable of type Scanner
      • // Connect the scanner to the keyboard
      • Scanner scan = new Scanner(System.in);
    • Read the scanner
        • String data = scan.nextLine();
  • 18. Reading Streams
    • Read the scanner, again
          • // get the next token, hope it’s an integer
          • int i = scan.nextInt();