Date post: | 19-Jan-2018 |
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COMMON MISTAKES
CSC 111 - JavaProgram Structure String Methods
By: Arwa Alturki 2
Program Structure
• Read and understand the problem• In all programs their should be:– Named class – Main method
import java.util.*;public class Revision{ public static void main (String [] args){ Scanner input = new Scanner(System.in); }}
By: Arwa Alturki 3
Program Structure
• Brackets after both of class and main method
import java.util.*;public class Revision{ public static void main (String [] args){ Scanner input = new Scanner(System.in); }}
import java.util.*;public class Revision; public static void main (String [] args); Scanner input = new Scanner(System.in); }}
✓
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By: Arwa Alturki 4
Variables
• Preserve naming convention• Constant variablepublic class Revision{ public static void main (String [] args){ final double DOLLAR_PRICE = 3.75; }}
public class Revision; public static void main (String [] args); double DOLLAR_PRICE = 3.75; }}
✓
✗?
By: Arwa Alturki 5
Variables
• Casting variable DO NOT change its type
public class Revision{ public static void main (String [] args){ char ch = 'A'; double num = (double) ch + 3.5; System.out.println("The charachter is " + ch); System.out.println("The number is " + num); }}
OUTPUT:The character is AThe number is 68.5
By: Arwa Alturki 6
Variables
• Complete division
public class Revision{ public static void main (String [] args){ int init_price = 150; int sale = 15; double final_price = 150 - (150 * 15 / 100.00); System .out.println("The price is " + final_price); }}
OUTPUT:The price is 127.5 SR
By: Arwa Alturki 7
Variables
• Integer division
public class Revision{ public static void main (String [] args){ int init_price = 150; int sale = 15; double final_price = 150 - (150 * 15 / 100); System .out.println("The price is " + final_price); }}
OUTPUT:The price is 128 SR
By: Arwa Alturki 8
Input
• Display message to the user before reading
import java.util.*;public class Revision{ public static void main (String [] args){ Scanner input = new Scanner(System.in); int ID; String name; System.out.print("Enter your name: "); name = input.next(); System.out.print("Enter your ID: "); ID = input.nextInt(); }}
✓
By: Arwa Alturki 9
Input
• Display message to the user before reading
import java.util.*;public class Revision{ public static void main (String [] args){ Scanner input = new Scanner(System.in); int ID; String name; name = input.next(); System.out.print("Enter your name: "); ID = input.nextInt(); }}
✗?
By: Arwa Alturki 10
Input
• One Scanner object for all readings
import java.util.*;public class Revision{ public static void main (String [] args){ Scanner input = new Scanner(System.in); int ID; String name; System.out.print("Enter your name: "); name = input.next(); System.out.print("Enter your ID: "); ID = input.nextInt(); }}
✓
By: Arwa Alturki 11
Input
• One Scanner object for all readings
import java.util.*;public class Revision{ public static void main (String [] args){ Scanner input1 = new Scanner(System.in); Scanner input2 = new Scanner(System.in); int ID; String name; System.out.print("Enter your name: "); name = input1.next(); System.out.print("Enter your ID: "); ID = input2.nextInt(); }}
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By: Arwa Alturki 12
Input
• Use nextLine method to read a line of strings– next method read until the first space in the line
import java.util.*;public class Revision{ public static void main (String [] args){ Scanner input = new Scanner(System.in); System.out.print("Enter your full name: "); String str = input.nextLine(); }}
By: Arwa Alturki 13
Output
• Use comma (,) NOT plus (+) in printfpublic class Revision{ public static void main (String [] args){ int year = 2014; double days = 365.25; System.out.printf("We are on %d where there are %.2f days", year, days);}}
public class Revision{ public static void main (String [] args){ int year = 2014; double days = 365.25; System.out.printf("We are on %d where there are %.2f days" + year + days);}}
✓
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By: Arwa Alturki 14
String Operations
• Make your solution general as possible as you can– Use the given format
import java.util.*;public class Revision{ public static void main (String [] args){ Scanner input = new Scanner(System.in); System.out.print("Enter the time as hh:mm: "); String str = input.next(); int index = str.indexOf(':'); String h = str.substring(0,index); String m = str.substring(index+1); System.out.print("The hour now is “+h+" and “+m); }}
✓
By: Arwa Alturki 15
String Operations
• Make your solution general as possible as you can– Use the given format
import java.util.*;public class Revision{ public static void main (String [] args){ Scanner input = new Scanner(System.in); System.out.print("Enter the time as hh:mm: "); String str = input.next(); String h = str.substring(0,2); String m = str.substring(3); System.out.print("The hour now is “+h+" and “+m); }}
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By: Arwa Alturki 16
String Operations
• Str.IndexOf(char)
public class Revision{ public static void main (String [] args){ String str = "1:15"; int index = str.indexOf(':'); }}
public class Revision{ public static void main (String [] args){ String str = "1:15"; int index = str.indexOf(:); }}
✓
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By: Arwa Alturki 17
String Operations
• Str.IndexOf(char, index to start from)public class Revision{ public static void main (String [] args){ String str = "1:15:30"; int index1 = str.indexOf(':'); int index2 = str.indexOf(':', index1+1); }}
public class Revision{ public static void main (String [] args){ String str = "1:15:30"; int len = str.length(); int index1 = str.indexOf(':'); int index2 = str.indexOf(':', len); }}
✓
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By: Arwa Alturki 18
String Operation
• Parsing (convert string to number)
public class Revision{ public static void main (String [] args){ String str = "135"; int num1 = Integer.parseInt(str); double num2 = Double.parseDouble("125.75"); }}
public class Revision{ public static void main (String [] args){ String str = "135"; int num1 = Integer.parseInt("str"); double num2 = Double.parseDouble(125.75); }}
✓
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By: Arwa Alturki 19
String Operations
• Remember:– indexOf method returns int value, which is the
index of the given character– charAt method returns char value, which is the
character at the given index– Substring method return string NOT numbers
By: Arwa Alturki 20
Control Structure (If/Else)
• Use compareTo or equals method to compare two strings
public class Revision{ public static void main (String [] args){ String str = "Test String Comparison"; if (str.compareTo("Test String") == 0) System.out.println("Similar strings");}}
public class Revision{ public static void main (String [] args){ String str = "Test String Comparison"; if (str.equals("Test String")) System.out.println("Similar strings");}}
✓
✓
By: Arwa Alturki 21
Control Structure (If/Else)
• Use compareTo or equals method to compare two strings
public class Revision{ public static void main (String [] args){ String str = "Test String Comarision"; if (str == "Test String") System.out.println("Similar strings"); }}
✗
By: Arwa Alturki 22
QUESTIONS ?!
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