2.  Course outline/course web page “Quiz” using your clicker  Start Chap. 1 2

3.  Reminder: Course Website at https://www.myconcordia.ca/ https://www.myconcordia.ca/  Any questions on course outline?  ENCS login 3

4. My last name is? A. Aceman B. Acemin C. Acemain D. Acemian E. Don’t know! 4

5. My office hours are on which days? A. Mon to Wed B. Mon to Thur C. Mon – Wed – Fri D. You have office hours? University students don’t need office hours! E. Don’t know! 5

6. How many assignments are there? A. Assignments? None – We don’t need any B. 3 C. 4 D. 5 E. Don’t know 6

7. How many term tests are there? A. 1 B. 2 C. 3 D. 4 E. Don’t know! 7

8. How much of the course grade is the final exam worth? A. 60% B. 55% C. 45% D. 30% E. Don’t know! 8

9. Where can I get help/advise if I need it? A. From my teacher B. From my tutors C. help4u D. All of the above E. I’m in University now! I’m on my own 9

10. Which animal can be found in the course web page? A. Dog B. Elephant C. Cat D. Panda E. How should I know? 10

11.  Keep up as material is cumulative  Program the examples in the slides and ‘play’ with them  Study in groups  You don’t understand something get help right away from your teacher, tutor, study group member as soon as possible. 11

12. 12 = the slides will be completed in class = clicker question

13. Chapter 1: A First Program

14.  Humans communicate in a natural language  Large vocabulary (10 000s words)  Complex syntax  Semantic ambiguity  The chair’s leg is broken.  The man saw the boy with the telescope.  Machines communicate in binary code / machine language  Small vocabulary (2 words… 1, 0)  Simple syntax  No semantic ambiguity 14

15. Programming language  Ex: ???  Vocabulary: restricted  Syntax: small and restricted  Semantic: no ambiguity (almost) 15 Humans -- natural language  Large vocabulary  Complex syntax  Semantic ambiguity Machines -- binary language  Small vocabulary  Simple syntax  No semantic ambiguity Programming (COMP 248 + COMP 249) Compiler + Interpreter

16.  Created by Sun Microsystems (1991)  Originally designed for programming home appliances  Introduced in 1995 and its popularity has grown quickly since  Is an object-oriented programming (OOP) language 16

17.  A compiler:  is a software tool which translates source code into another language  Usually (ex. C, C++)  The compiler translates directly into machine language  But each type of CPU uses a different machine language  … so same executable file will not work on different platforms  … need to re-compile the original source code on different platforms  Java is different… 17

18.  Java compiler:  Java source code --> bytecode  A machine language for a fictitious computer called the Java Virtual Machine  Java interpreter:  Executes the Java Virtual Machine (JVM)  Java bytecode --> into machine language and executes it  Translating byte-code into machine code is relatively easy compared to the initial compilation step  So the Java compiler is not tied to any particular machine  Once compiled to byte-code, a Java program can be used on any computer, making it very portable 18

19. 19 Java source Code MyProg.java Machine Code Java Bytecode MyProg.class Java Interpreter java MyProg Java Compiler javac MyProg.java

20.  Algorithm:  A step-by-step process for solving a problem  Expressed in natural language  Pseudocode:  An algorithm expressed in a more formal language  Code-like, but does not necessarily follow a specific syntax  Program:  An algorithm expressed in a programming language  Follows a specific syntax 20

21.  The purpose of writing a program is to solve a problem  The general steps in problem solving are: 1.Understand the problem 2.Design a solution (find an algorithm) 3.Implement the solution (write the program) 4.Test the program and fix any problems 21

22.  A java program:  is made up of one or more classes (collection of actions)  a class contains one or more methods (action)  a method contains program statements/instructions  A Java program always contains a method called main 22

23. 23 public class MyProgram {}{} // comments about the class class header class body MyProgram.java

24. 24 public class MyProgram {}{} public static void main (String[] args) {}{} // comments about the class // comments about the method method header method body MyProgram.java

25. //******************************************************************** // Author: L. Kosseim // // Demonstrates the basic structure of a Java application. //******************************************************************** public class Hello { //----------------------------------------------------------------- // Prints a message on the screen //----------------------------------------------------------------- public static void main (String[] args) { System.out.println ("Hello World!!!"); } 25 Java is case sensitive! You will type and run this program in tutorial 1 Hello.java extension of java programs

26.  Syntax rules  define how we can put together symbols, reserved words, and identifiers to make a valid program  Semantics  define what a statement means  A program that is syntactically correct is not necessarily logically (semantically) correct. 26

27.  Compile-time (syntax) errors  The compiler will find syntax errors and other basic problems  An executable version of the program is not created  Ex: ??  Run-time errors  A problem can occur during program execution  Causes the program to terminate abnormally  Ex: ?? 27

28.  Logical (semantic) errors… aka a bug  A mistake in the algorithm  Compiler cannot catch them  A program may run, but produce incorrect results  Ex: ??  The process of eliminating bugs is called debugging  (who found the first bug?) 28 Grace Hooper (1906-1992) American Computer Scientist & US Navy Admiral

29. The hardest kind of error to detect in a computer program is a: A) Syntax error B) Run-time error C) Logic error D) All of the above 29

30. 30 Compilation errors Run-time & logical errors Edit and save program Compile program Execute program and evaluate results

31.  Basic compiler & interpreter  Sun Java Development Kit (JDK) -- download from Sundownload from Sun  Compiler: javac Hello.java  The result is a byte-code program called: Hello.class  Interpreter: java Hello 31

32.  IDE (Integrated Development Environment)  Eclipse  JCreator  Borland JBuilder  Microsoft Visual J++  … see course Web site to download them  In tutorial 1, you will edit, compile and run Hello.java Hello.java 32

33.  In Java, we have 2 types of programs: 1.applications  "autonomous applications" or stand-alone program  executed by the local OS (through the Java Virtual Machine)  can use graphics and GUI or just plain console I/O  must have a main method  what we will see in COMP 248  ex: FirstProgram.java FirstProgram.java 33

34. 2.applets  "internet applications"  executed by a Web browser (through the Java Virtual Machine)  must be inserted into an HTML page  must use a GUI  ex: PocketCalc.java + Calculator.html PocketCalc.java Calculator.html 34

35. COMP 248: Object Oriented Programming I

36. 1. Comments 2. Identifiers 3. Indentation 4. Primitive Types 5. Variables 6. Output 7. Assignment 8. Arithmetic Expressions 9. More Assignment Operators 10. Assignment Compatibility 11. Strings 36

37. //************************************************** // comments on the program (authors, purpose, …) //************************************************** public class SomeIdentifier { //----------------------------------------------- // comments on the main method //----------------------------------------------- public static void main (String[] args) { // declarations of variables and constants // statements of the main method } 37 SomeIdentifier.java

38.  also called inline documentation  used to explain the purpose of the program and describe processing steps (the algorithm)  do not affect how a program works (are ignored by the compiler)  can take 3 forms: 38 // this comment runs to the end of the line /* this comment runs to the terminating symbol, even across line breaks */ /** this is a javadoc comment */

39.  are the words a programmer uses in a program to name variables, classes, methods, …  Rules to create an identifier:  can be made up of:  letters,  digits,  the underscore character (_),  and the dollar sign ($)  cannot begin with a digit  cannot be a reserved word  no limit on length 39

40. Which of the following is not a valid identifier? A) abc B) ABC C) Abc D) aBc E) a bc 40

41. Which of the following is not a valid identifier? A) a_bc B) A$BC C) _Abc D) 1AbC E) $abc 41

42.  Guidelines:  give a significant name!  avoid '$‘  by convention:  class names --> use title case  ex: MyClass, Lincoln  constants --> use upper case  ex: MAXIMUM  variables, methods, … --> start with lowercase  ex: aVar, a_var 42

43.  Avoid Predefined identifiers:  Although they can be redefined, it is confusing and dangerous  System String println  Remember: Java is case sensitive 43

44. 44 abstract assert boolean break byte case catch char class const continue default do double else extends false final finally float for goto if implements import instanceof int interface long native new null package private protected public return short static strictfp super switch synchronized this throw throws transient true try void volatile while

45. 45 IdentifierCorrect or not? GST PriceBeforeTax Student_3 student#3 Shipping&HandlingFee Class __123 the account 1floor

46.  Spaces, blank lines, and tabs are called white space  White space is used to separate words and symbols in a program  Extra white space is ignored  Programs should be formatted to enhance readability, using consistent indentation 46

47. //****************************************************** // Lincoln2.java // Demonstrates a poorly formatted, though valid, // Program. //****************************************************** public class Lincoln2{public static void main(String[]args){ System.out.println("A quote by Abraham Lincoln:"); System.out.println("Whatever you are, be a good one.");}} 47

48. //******************************************************************** // Lincoln3.java // Demonstrates another valid program that is poorly formatted. //******************************************************************** public class Lincoln3 { public static void main ( String [] args ) { System.out.println ( "A quote by Abraham Lincoln:" ) ; System.out.println ( "Whatever you are, be a good one." ) ; } 48

49. //***************************************************** // Lincoln3.java // Demonstrates a properly formatted program. //***************************************************** public class Lincoln3 { public static void main(String[]args) { System.out.println("A quote by Abraham Lincoln:"); System.out.println("Whatever you are, be a good one."); } 49

50.  8 primitive data types in Java  Numeric  4 types to represent integers (ex. 3, -5):  byte, short, int, long  2 types to represent floating point numbers (ex. 3.5):  float, double  Characters (ex. 'a' )  char  Boolean values (true/false)  boolean 50

51.  The difference between:  byte, short, int, long AND float, double is their size (so the values they can store) 51

52.  The difference between:  byte, short, int, long AND float, double is their size (so the values they can store) 52

53.  Floating point numbers are only approximate quantities  Mathematically, the floating-point number 1.0/3.0 is equal to 0.3333333...  A computer may store 1.0/3.0 as something like 0.3333333333 53

54.  A char stores a single character  delimited by single quotes: 'a' 'X' '7' '$' ',' '\n'  characters are ordered according to a character set  each character corresponds to a unique number code  Java uses the Unicode character set  16 bits per character, so 65,536 possible characters  Unicode is an international character set, containing symbols and characters from languages with different alphabets 54

55.  The ASCII character set is older and smaller than Unicode, but is still popular  The ASCII characters are a subset of the Unicode character set, including: 55 uppercase letters lowercase letters punctuation digits special symbols control characters ’A’, ’B’, ’C’, … ’a’, ’b’, ’c’, … ’. ’, ’; ’, … ’0’, ’1’, ’2’, … ’&’, ’|’, ’\’, … ’\n’, ’\t’, …

56.  A boolean value represents a true or false expression  The reserved words true and false are the only valid values for a boolean type  NOT… 0 and 1 56

57.  a name for a location in memory  used to store information (ex. price, size, …)  must be declared before it is used  indicate the variable's name  indicate the type of information it will contain  declaration can be anywhere in the program (but before its first access) 57 int total; int count, temp, result; Multiple variables can be created in one declaration data type variable name

58.  A variable that has been declared but has not yet been given a value is said to be uninitialized  In certain cases an uninitialized variable is given a default value  It is best not to rely on this  Explicitly initialized variables have the added benefit of improving program clarity 58

59.  A variable can be given an initial value in the declaration 59 When a variable is used in a program, its current value is used int sum = 0; int base = 32, max = 149;

60. //************************************************************ // PianoKeys.java // // Demonstrates the declaration and initialization of an // integer variable. //*********************************************************** public class PianoKeys { // Prints the number of keys on a piano. public static void main (String[] args) { int keys = 88; System.out.println("A piano has" + keys + "keys."); } 60 ??? Output filename??

61.  similar to a variable but can only hold one value while the program is active  the compiler will issue an error if you try to change the value of a constant during execution  use the final modifier  Constants:  give names to otherwise unclear literal values  facilitate updates of values used throughout a program  prevent inadvertent attempts to change a value 61 final int MIN_AGE = 18;

62.  Examples: 62 System.out.print Displays what is in parenthesis System.out.println Displays what is in parenthesis Advances to the next line System.out.print("hello"); System.out.print("you"); System.out.println("hello"); System.out.println("you"); System.out.println(); int price = 50; System.out.print(price); char initial = 'L'; System.out.println(initial); Output

63. 63 System.out.println("hello" + "you"); double price = 9.99; int nbItems = 5; System.out.println("total = " + price*nbItems + "$"); int x = 1, y = 2; System.out.println("x+y="+x+y); System.out.println("x+y="+(x+y)); in print and println, + is the concatenation… you need parenthesis for the + to be addition ??? Output

64. 64 cannot cut a string over several lines System.out.println("this is a long string"); // error! System.out.println("this is a" + "long string"); // ok

65.  to print a double quote character  Use an escape sequence  sequence is a series of characters that represents a special character  begins with a backslash character ( \ )  considered as 1 single character 65 System.out.println ("I said "Hi" to her."); System.out.println ("I said \"Hi\" to her."); ??? Output ??? Output

66.  Some Java escape sequences: 66 Escape Sequence \b \t \n \" \' \\ Meaning backspace tab newline double quote single quote backslash

67. What will the following statement output? A)one two three B) one\ntwo\nthree\n C) "one\ntwo\nthree\n" D) one two three E)onetwothree 67 System.out.print("one\ntwo\nthree\n");

68. What statement will result in the following output? System.out.print A) ( " Read the file " c:\windows\readme.txt "); B) ( " Read the file " c:\windows\readme.txt ""); C) ( " Read the file " c:\\windows\\readme.txt "); D) ( " Read the file \ " c:\\windows\\readme.txt\ ""); E) ( " Read the file \ " c:\windows\readme.txt\ ""); 68 Read the file " c:\windows\readme.txt "

69.  Used to change the value of a variable  The assignment operator is the = sign 69 total = 55; Syntax: Variable = Expression; Semantics: 1. the expression on the right is evaluated 2. the result is stored in the variable on the left (overwrite any previous value) 3. The entire assignment expression is worth the value of the RHS

70. public class Geometry { // Prints the number of sides of several geometric shapes. public static void main (String[] args) { int sides = 7; // declaration with initialization System.out.println("A heptagon has " + sides + " sides."); sides = 10; // assignment statement System.out.println("A decagon has " + sides + " sides."); sides = 10+2; System.out.println("A dodecagon has " + sides + " sides."); } 70 ??? Output filename???

71.  In Java, = is an operator  In math, = is an equality relation 71 In math… a+6 = 10 ok In Java… a+6 = 10; In math… a = a+1 always false In Java… a = a+1; In math… a = b and b = a same thing! In Java… a = b; and b = a;

72.  Declarations:  Statements : 72 int x; int y = 10; char c1 = ’a’; char c2 = ’b’; x = 20+5; y = x; c1 = ’x’; c2 = c1;

73.  Write a series of declarations & statements to swap the value of 2 variables… int x = 10; int y = 20; A) x = y; y = x; B) y = x; x = y; C) Both A) & B) will work D) Neither A) nor B) will work 73

74.  An expression is a combination of one or more operands and their operators  Arithmetic operators: 74 Addition+ Subtraction- Multiplication* Division/ Remainder%

75.  the division operator ( / ) can be:  Integer division  if both operands are integers  Real division  otherwise 75 10 / 8 equals? 8 / 12 equals? 1 0 10.0 / 8 equals? 8 / 12.0 equals? 1.25 0.6667

76. 76 the remainder operator (%)  returns the remainder after the integer division 10 % 8 equals? 8 % 12 equals? 2 (10÷8 = 1 remainder 2) 8

77.  Operators can be combined into complex expressions  precedence determines the order of evaluation  1 st : expressions in parenthesis  2 nd : unary + and -  3 rd : multiplication, division, and remainder  4 th : addition, subtraction, and string concatenation  5 th : assignment operator 77 result = total + count / max - offset;

78.  Unary operators of equal precedence are grouped right-to- left +-+rate is evaluated as +(-(+rate))  Binary operators of equal precedence are grouped left-to- right base + rate + hours is evaluated as (base + rate) + hours  Exception: A string of assignment operators is grouped right-to-left n1 = n2 = n3; is evaluated as n1 = n2 = n3; 78

79.  What is the order of evaluation in the following expressions? 79 a + b + c + d + e a + b * c - d / e a / (b + c) - d % ea / (b * (c + (d - e)))

80.  The assignment operator has a lower precedence than the arithmetic operators 80 First the expression on the RHS is evaluated Then the result is stored in the variable on the LHS answer = sum / 4 + MAX * lowest; 1432

81. What is stored in the integer variable num1 after this statement? num1 = 2 + 3 * 5 - 5 * 2 / 5 + 10 ; A) 0 B) 18 C) 25 D) 10 81

82.  Purpose:  Conversion of degrees Fahrenheit in degrees Celsius  Algorithm: 1. Assign the temperature in Fahrenheit (ex. 100 degrees) 2. Calculate the temperature un Celsius (1 Celsius = 5/9 (Fahr – 32) 3. Display temperature in Celsius  Variables and constants: 82 DataIdentifierTypevar or const? Temperature in Fahrenheit fahrdouble

83. //********************************************************** // Temperature.java Author: your name // A program to convert degrees Fahrenheit in degrees Celsius. //********************************************************** public class Temperature { public static void main (String[] args) { // Declaration of variables and constants float temperature; Scanner sc = new Scanner(System.in); // step 1: Assign the temperature in Fahrenheit (100) System.out.println("Enter temperatue in Fahrenheit = "); temperature = sc.nextInt(); // OR temperature = 100; // step2: Calculate the temperature un Celsius temperature = ((temperature - 32)*5)/9; // step3: Display temperature in Celsius System.out.println("Temperatue in Celsius = " + temperature); } 83 filename???

84.  in addition to =  often we perform an operation on a variable, and then store the result back into that variable  Java has shortcut assignment operators: variable = variable operator expression; variable operator= expression; 84 Operator += -= *= /= %= Example x += y x -= y x *= y x /= y x %= y Equivalent To x = x + y x = x - y x = x * y x = x / y x = x % y

85. Example:Equivalent To: count += 2;count = count + 2; sum -= discount;sum = sum – discount; bonus *= 2;bonus = bonus * 2; time /= rushFactor;time = time / rushFactor; change %= 100;change = change % 100; amount *= count1 + count2;amount = amount * (count1 + count2); 85

86.  The behavior of some assignment operators depends on the types of the operands  ex: the +=  If the operands are strings, += performs string concatenation  The behavior of += is consistent with the behavior of the "regular" + 86

87. int amount = 10; amount += 5; System.out.println(amount); double temp = 10; temp *= 10; System.out.println(temp); String word = "hello"; word += "bye"; System.out.println(word); word *= "bye"; // ??? 87 Output

88.  In Java, we often add-one or subtract-one to a variable…  2 shortcut operators:  The increment operator ( ++ ) adds one to its operand  The decrement operator ( -- ) subtracts one from its operand  The statement: count++; is functionally equivalent to: count = count+1;  The statement: count--; is functionally equivalent to: count = count-1; 88

89.  The increment and decrement operators can be in: 1. in prefix form - ex: ++count; 1. the variable is incremented/decremented by 1 2. the value of the entire expression is the new value of the variable (after the incrementation/decrementation) 2. in postfix form: - ex: count++; 1. the variable is incremented/decremented by 1 2. the value of the entire expression is the old value of the variable (before the incrementation/decrementation) 89

90. 90 int nb = 50; ++nb; int nb = 50; int x; x = ++nb; int nb = 50; nb++; int nb = 50; int x; x = nb++; int nb = 50; int x; x = nb++ + 10; value of nb value of nb & x

91. What is stored in the integer variables num1, num2 and num3 after the following statements? int num1 = 1, num2 = 0; int num3 = 2 * num1++ + - -num2 * 5; A)num1 = 1, num2 = 0, num3 = 2 B) num1 = 1, num2 = 0, num3 = -1 C) num1 = 2, num2 = -1, num3 = 2 D) num1 = 2, num2 = -1, num3 = -3 E) num1 = 2, num2 = -1, num3 = -1 91

92. What is stored in the integer q after the following statements? int x = 1, y = 10, z = 3; int q = ++x * y- - + z++; A)13 B) 20 C) 23 D) No idea??? 92

93. What is stored in the integers a and c after the following statements? int a = 1; int c = a++ + a- - ; A)a = 1, c = 2 B) a = 1, c = 3 C) a = 3, c = 3 D) No idea??? 93

94. What is stored in the integer c after the following statements? int a = 1, b = 2; int c = a++ + a + 2*(- - b) + 3/b- - ; A)7 B) 8 C) 8.5 D) No idea??? 94

95. 95 Expression count++ ++count count-- --count Operation add 1 subtract 1 Value Used in Expression old value new value old value new value

96.  In general, the value of one type cannot be stored in a variable of another type int intVariable = 2.99; //Illegal  However, there are exceptions to this double doubleVariable = 2;  For example, an int value can be stored in a double type 96

97.  an expression has a value and a type  the type of the expression depends on the type of its operands  In Java, type conversions can occur in 3 ways:  arithmetic promotion  assignment conversion  casting 97 2 / 4 (value = 0, type = int) 2 / 4.0 (value = 0.5, type = double)

98.  happens automatically, if the operands of an expression are of different types  operands are promoted so that they have the same type  promotion rules:  if 1 operand is of type… the others are promoted to…double floatfloat (double)long  short, byte and char are always converted to int 98 aLong + anInt * aDouble

99.  value and type of these expressions? 99 2 / 4 int / int 2/4 int 0 (aByte + anotherByte) --> int (aLong + anInt * aDouble) --> ?? (aFloat - aBoolean) --> ??

100.  What is the value and type of this expression? 2 / 4 * 1.0 A) 0 (int) B) 0.0 (double) C) 0.5 (int) D) 0.5 (double) 100

101.  What is the value and type of this expression? 1.0 * 2 / 4 A) 0 (int) B) 0.0 (double) C) 0.5 (int) D) 0.5 (double) 101

102. 102 occurs when an expression of one type is assigned to a variable of another type widening conversion  if the variable has a wider type than the expression  then, the expression is widened automatically  integral & floating point types are compatible  boolean are not compatible with any type long aVar; aVar = 5+5; byte aByte; int anInt; anInt = aByte; double aDouble; int anInt = 10; aDouble = anInt; var = expression;

103. 103 int aVar; aVar = 3.7; ok? int aVar; aVar = 10/4; ok? int aVar; aVar = 10.0/4; ok? narrowing conversion  if the variable has a smaller type than the expression then, compilation error, because possible loss of information

104. 104 the programmer can explicitly force a type conversion syntax: (desired_type) expression_to_convert Casting can be dangerous! you better know what you're doing… double d; d = 2/4; // d is 0 d = (double)2/4; // d is 0.5 // 2.0 / 4 d = (double)(2/4); // d is 0.0 int aVar; aVar = (int)3.7; (aVar is 3… not 4!) byte aByte; int anInt = 75; aByte = anInt; // ok? aByte = (byte)anInt; // ok?

105.  Which of the following assignment statements are valid? byte b1 = 1, b2 = 127, b3; b3 = b1 + b2; // statement a) b3 = 1 + b2 // statement b) b3 = (byte)1 + b2 // statement c) A) Statements a), b) and c) are valid B) Only statements a) and b) are valid C) Only statements b) and c) are valid D) Only statements a) and c) are valid E) None of the Java statements are valid 105

106.  so far we have seen only primitive types  a variable can be either:  a primitive type  ex: int, float, boolean, …  or a reference to an object  ex: String, Array, …  A character string:  is an object defined by the String class  delimited by double quotation marks ex: "hello", "a"  System.out.print("hello"); // string of characters  System.out.print('a'); // single character 106

107. 1. declare a reference to a String object 2. declare the object itself (the String itself) 107 String title; title = new String("content of the string"); This calls the String constructor, which is a special method that sets up the object

108.  Because strings are so common, we don't have to use the new operator to create a String object  These special syntax works only for strings 108 String title; title = new String("content of the string"); String title; title = "content of the string"; String title = new String("content of the string"); String title = "content of the string";

109.  once a string is created, its value cannot be modified (the object is immutable)  cannot lengthen/shorten it  cannot modify its content  the String class offers:  the + operator (string concatenation)  ex: String solution = "The answer is " + "yes";  many methods to manipulate strings, a string variable calls …  length() // returns the nb of characters in a string  concat(str) // returns the concatenation of the string and str  toUpperCase() // returns the string all in uppercase  replace(oldChar, newChar) // returns a new string // where all occurrences of character oldChar have been replaced by character newChar  … see p. 38 … 109

110. 110

111. public class StringTest { public static void main (String[] args) { String string1 = new String ("This is a string"); String string2 = ""; String string3, string4, string5; System.out.println("Content of string1: \"" + string1 + "\""); System.out.println("Length of string1: " + string1.length()); System.out.println("Content of string2: \"" + string2 + "\""); System.out.println("Length of string2: " + string2.length()); 111 Content of string1:"This is a string" Length of string1: 16 Content of string2: "" Length of string2: 0 Output

112. // String string1 = new String ("This is a string"); // String string2 = ""; string2 = string1.concat(" hello"); string3 = string2.toUpperCase(); string4 = string3.replace('E', 'X'); string5 = string4.substring(3, 10); System.out.println(string2); System.out.println(string3); System.out.println(string4); System.out.println(string5); } } 112 This is a string hello THIS IS A STRING HELLO THIS IS A STRING HXLLO S IS A Output