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Know for Quiz 2 • Everything through Exam 1 • 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 • 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 Find a character or substring in String Convert to lower or upper case 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 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 String Methods • charAt(int index): return char at named index (starting at 0) • equals(String str): return boolean • indexOf(char): return int of first occurrence of char (index starts at 0) • indexOf(String substr): return int of first occurrence of String substr • length(): return int length of String • substring(int start, int end): return String between start and end • toLowerCase(), toUpperCase(): convert String 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 compareString = myString.toLowerCase(); System.out.println("String is: " + compareString); System.out.println("Char S is at location: " + myString.indexOf('S')); System.out.println("substring og is at location: " + myString.indexOf("og")); System.out.println("Length of string is: " + myString.length()); System.out.println("substring between location 3 and 5 is: " + myString.substring(3,5)); Output: String is: my dog sandy Char S is at location: 7 Substring og is at location: 4 Length of string is: 12 Substring between location 3 and 5 is: Do 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 } } More on Input • • • • • Input Failure Common *MUST* Be Part of Test Plan Pages 310-313 in Anderson Check Input for Type Desired If not, Notify User, and Get Rid of Line 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); } 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; Disk string firstname; Input Files import java.io.*; import java.util.Scanner; class FileInput { public static void main(String [ ] args) throws IOException { File ifile = new File("data.txt"); Scanner scan = new Scanner(ifile); while (scan.hasNextInt()) { i = scan.nextInt(); } } 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 } import java.util.Scanner; import java.io.*; mydata.txt file class FormatFileData { public static void main(String [ ] args) throws IOException { int loops, integer, i; float decimal; String name; 5 8 9.3 Jon 6 14.335 Bill 0 35.67e9 Mary -23 -4.55 Smith -3 -4e3 xyz 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 Know for Quiz 2 • Everything through Exam 1 • Loops: while, for, do-while • switch-case Statement