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Announcements

This announcement provides information on the built-in data types for variables in Java, naming variables and constants, input and output, and expressions. It also mentions what students should know for the upcoming quiz.

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Announcements

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  1. Announcements • Quiz 1 Next Monday

  2. Built-In (or Primitive) Data Types for Variables • int: Integer Range of Typically –2,147,483,648 to 2,147,483,647 (machine and compiler dependent) • float: Real Number (i.e., integer part, decimal part, and exponent part) Range of Typically (+/-) 10e-45 to 10e38 • double: Larger Real Number ((+/-) 10e-324 to 10e308) • char: Character

  3. Naming Variables in JAVA: Identifiers • Can Use Letters: Remember That JAVA is Case Sensitive (e.g., NumWidgets Is Not the Same as numwidgets) • Can Use Digits 0-9, $, and Underscore • Cannot Start with a Digit • Cannot Contain Spaces or Other Characters • Cannot Use JAVA Keywords

  4. Naming Variables (Cont) • Should Use a Meaningful, Descriptive Name so that Variable’s Use Is Easily Understood: • Examples: counter, second, minute, length, width • Be Consistent with Case; Usually Lower Case with Upper Case for Second Part of Variable Name • Examples: averageRainfall, totalStudentGrades, maxBuildingHeight, minPackageWeight;

  5. Named Constants • Constant: An Identifier that Is Initialized to a Value that Cannot Change • Usually Declared at Top of Program using Keyword final • Standard Naming of Constants Is to Use All Upper Case Letter with or without Underscore between Words • All Constants Should Be Initialized • Syntax: final int MAXHT = 100;

  6. Advantages of Constants • Easier to Understand • Easier to Modify • Example: Compare using Number 100 in Program versus Constant MAXHT

  7. Named Constants public class MyProgram { public static void main( String [ ] args) { final int MAXHT = 100; ... currentHeight > MAXHT ... bridgeHeight == MAXHT ... bridgeHeight + newAddition >= MAXHT ... // used MAXHT 223 times in this program } }

  8. Literal Constants (Values) • Constants Whose values Are Already Known: Characters (Specified Inside Single Quotes): ‘A’ , ‘a’ , ’5’ , ’ ‘ , ’\n’ (newline) , ’\0’ (NULL Character) Integers: 10, 1345, -34 Float or Double: 2.3, -45.18, 10.6e6 String (Specified Inside Double Quotes): “HELLO” , “What a great deal.” , “5”

  9. Input and Output • Also Known as I/O • Output : System.out.println(“Hello World!!”); • Input (Scanner): import java.util.Scanner; Scanner scan = new Scanner(System.in); scan.nextInt(); scan.nextFloat(); scan.nextDouble(); scan.next(); //String to whitespace scan.nextLine(); // String to end of line • All Wait until User Inputs Particular Type

  10. Input and Output Example import java.util.Scanner; public class MyProgram { public static void main( String [ ] args) { Scanner scan = new Scanner(System.in); int numEntered; System.out.print(“Enter an integer:”); /// The following waits until user hits Enter numEntered = scan.nextInt(); System.out.println(“You entered: “ + numEntered); } }

  11. Characters and Strings • Strings in java.lang package • Java.lang imported automatically

  12. JAVA Strings • Declaration: String yourName; • Assigning a Value to a String: yourName = “A. Goose”; • String Constants (Values) Must Be Enclosed in Double Quotes

  13. Input String Example import java.util.Scanner; public class MyProgram { public static void main( String [ ] args) { Scanner scan = new Scanner(System.in); String lastname; System.out.print(“Enter last name:”); lastname = scan.next(); System.out.println(“You entered: “ + lastname); } }

  14. Expressions • Expression: A Sequence of One or More Identifiers and Operators that Evaluates to a Value • Operator: A Symbol Expressing a Way to Modify a Value or Values (e.g., + for Addition) • Operand: A Value Being Modified by an Operator • Example Expressions: 5 currentHeight currentHeight + 10

  15. Arithmetic Expressions • Standard Arithmetic Operations Can Be Performed: Addition, Subtraction, Multiplication, Division • Standard Arithmetic Operators Can Be Used for These Operations: +, -, *, / • Others: % - “Modulo (Mod)” – Remainder after Integer Division -- Decrement (Subtract 1) ++ Increment (Add 1)

  16. Order of Operations • Precedence: Level of Importance of Operations Multiplicative Operators Have Higher Precedence than Additive Operators: *, /, % Higher +, - Lower • Associativity: Order of Operation for Equal Level Precedence Most Operators Have Left-to-Right Associativity Use Parentheses to Force Differing Precedence of Operations

  17. Know for the Quiz • All Terms (Underlined Items) • Variable Declaration, Initialization, and Assignment • Constant Declaration • Expressions • Operators • Input (Scanner) and Output (System.out) • Everything in Homework through Lab 2

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