String Objects in JAVA: Methods and Usage

1. (Dreaded) Quiz 2 • Next Monday

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 • Find a character or substring in String • Convert to lower or upper case

3. Objects • Objects: Types of Variables Made from Built-In Types • Variables Can be Declared as an Object Type • Objects Usually Have Methods/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 Inside of Parenthesis • 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 • 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

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. 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

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 • If not, Notify User, and Get Rid of Line • Use scan.hasNextInt(), scan.hasNextDouble(), scan.hasNextFloat()

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. Know for Quiz 2 • Everything through Exam 1 • Loops: while, for, do-while • switch-case Statement • String Methods • Input Failure Methods