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Know for Quiz

Know for Quiz. Everything through Last Week and Lab 7 Loops: while , for , do - while switch - case Statement. Strings Revisited. String Is a Type (Object) in JAVA Automatically imported in java.lang May Initialize or Assign with Double Quoted Values

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Know for Quiz

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  1. Know for Quiz • Everything through Last Week and Lab 7 • Loops: while, for, do-while • switch-case Statement

  2. Strings Revisited • String Is a Type (Object) in JAVA • Automatically imported in java.lang • May Initialize or Assign with Double Quoted Values • Can Add String to String with ‘+’ Operator • CANNOT Compare using Equality Operators (uses .equals() method instead) • Methods Available to • Access single characters • Get length of String • Compare Strings

  3. Objects • Objects: Types of Variables Made from Built-In Types • Variables Can be Declared as an Object Type • Objects Usually Have Functions Tied to Them • Member functions • Public functions • Interface functions • Methods • String Is an Example of an Object Type • StringVariable.length() Returns the Number of Characters in the String

  4. Methods • Also called Procedures, Functions • Have Parenthesis (e.g., method() ) • May be Passed Arguments, or Parameters • Parameters are values to initialize new variables in method • Parameters used to pass information to method

  5. String Methods • charAt(int index): return char at named index (starting at 0) • equals(String str): return boolean • length(): return int length of String

  6. String myString = "My Dog Sandy",compareString; • System.out.println("The fourth character is: " + myString.charAt(3)); • if (myString.equals("my dog sandy")) • System.out.println("Strings are equal"); • else • System.out.println("Strings are not equal"); • compareString = myString + myString; • System.out.println("Added strings are: " + compareString); • Output: • The fourth character is: D • Strings are not equal • Added strings are: My Dog SandyMy Dog Sandy

  7. System.out.println("Length of string is: " + myString.length()); Output: Length of string is: 12

  8. import java.util.Scanner; public class MyProgram { public static void main( String [ ] args) { Scanner scan = new Scanner(System.in); String lastname; boolean instructor = false; System.out.print(“Enter last name:”); lastname = scan.next(); if(lastname.equals(“hanrath”)) instructor = true; // privileged else instructor = false; // not privileged } }

  9. More on Input • Input Failure Common • *MUST* Be Part of Test Plan • Pages 310-313 in Anderson • Check Input for Type Desired • hasNextInt(), hasNextDouble() • If not, Notify User, and Get Rid of Line • Once hasNotXXX() returns true, safe to read in value

  10. Input Failure Example import java.util.*; class InputFailureExample { public static void main(String[] args) { int numE; String garbage; Scanner scan = new Scanner(System.in); System.out.print("Enter Integer: "); while (!scan.hasNextInt()) { garbage = scan.nextLine(); System.out.println("Please try again."); System.out.print("Enter Integer: "); } numE = scan.nextInt(); System.out.println("You entered: " + numE); } }

  11. Arrays • Syntax: typevariableName[] = new type [size]; • Syntax: type [ ] variableName = new type [size]; • Memory Is Set Aside for size Items of type • Each Variable Location in Array Is Accessed by Offsetting into the Array with an Integer Expression • Legitimate Offsets Are 0 to size-1

  12. Array Example int [] values = new int[15]; values[0] = 150; values[1] = 78; values[2] = 16; System.out.println( values[0]); values[3] = values[0] + 6;

  13. Array Example final int ARRAY_SIZE = 100; int offset; int [] numArray = new int [ARRAY_SIZE]; for(offset = 0; offset < ARRAY_SIZE; offset++) { numArray[offset] = 0; } for(offset = 0; offset < numArray.length; offset++) { numArray[offset] = offset; }

  14. Files • Data in Main Memory is “volatile” • File: Place for “permanent” data storage • C: drive, A: drive, Flash drive, etc. Main Memory File main() int num; string firstname; Disk

  15. Output File Streams import java.io.*; class FileOutput { public static void main(String [ ] args) throws IOException { int i; FileOutputStream ofile = new FileOutputStream("data2.txt",false); //true:APP PrintWriter pw = new PrintWriter(ofile); for (i=0;i < 100; i = i + 2) { pw.println(i); } pw.close(); // Writes data to file on disk } }

  16. Input Files import java.io.*; import java.util.Scanner; class FileInput { public static void main(String [ ] args) throws IOException { File ifile = new File("data2.txt"); Scanner scan = new Scanner(ifile); while (scan.hasNextInt()) { i = scan.nextInt(); } } }

  17. mydata.txt file 5 8 9.3 Jon 6 14.335 Bill 0 35.67e9 Mary -23 -4.55 Smith -3 -4e3 xyz import java.util.Scanner; import java.io.*; class FormatFileData { public static void main(String [ ] args) throws IOException { int loops, integer, i; float decimal; String name; File ifile = new File("mydata.txt"); Scanner scan = new Scanner(ifile); loops = scan.nextInt(); for(i= 0 ; i < loops; i++) { integer = scan.nextInt(); decimal = scan.nextFloat(); name= scan.next(); System.out.print(integer + " "); System.out.print(decimal + " "); System.out.print(name + " "); System.out.println(); } } } Output: 8 9.3 Jon 6 14.335 Bill 0 3.567E10 Mary -23 -4.55 Smith -3 –4000.0 xyz

  18. Know for Quiz 2 • Everything through Last Week and Lab 7 • Loops: while, for, do-while • switch-case Statement

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