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String Operations in JAVA Overview

Learn about string manipulation, methods, objects, and comparisons in Java programming. Arrays, file handling, and input failure handling are also covered. Includes code examples for practice.

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String Operations in JAVA Overview

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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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