2. Session 2 Session 2 Java Language Fundamentals 9:17 AM

3. Review Java was introduced by Sun Microsystems in 1995. Java is a programming language popularly used to build programs that can work on the Net. Its primary features are: it is object-oriented and a cross platform language. Swing, Drag and Drop, Java 2D API, Java Sound and RMI are some of the features added to the existing version of Java. A Java applet is designed to work in a pre-defined “sandbox” only. This makes it safe to be used on the Internet. Java bytecodes are machine language instructions understood by the Java Virtual Machine and usually generated as a result of compiling Java language source code. 9:17 AM

4. Review Contd… Java programs can be divided into following categories-applets, applications, GUI applications, servlets and database applications. Java visual development tools help the programmer to develop Java applications and applets more quickly and efficiently. The JDK contains the software and tools needed to compile, debug and execute applets and applications written in the Java language. It’s basically a set of command-line tools. Enhancement in Swing, AWT, a new I/O class and so on has been added in the latest version of Java 1.4.2. The future will use a lot of Java related programs for consumer gadgets with embedded technologies. 9:17 AM

5. Objectives Interpret the Java Program Understand the basics of Java Language Identify the Data Types Understand arrays Identify the Operators Format output using Escape Sequence 9:17 AM

6. A Sample Java program // This is a simple program called First.java class First { public static void main (String [] args) { System.out.println ("My first program in Java "); } 9:17 AM

7. Analyzing the Java Program The symbol // stands for commented line. When longer comments are needed, mark each line with a //. ◦ Or use the /* and */ comment delimiters -> block off a longer comment The line class First declares a new class called First. public static void main (String [] args) ◦ This is the main method from where the program begins its execution. System.out.println (“My first program in java”); ◦ object.method(parameters) ◦ This line displays the string My first program in java on the screen. 9:17 AM

9. Phase 1: Creating a Program consists of editing a file with an editor program (normally known simply as an editor). A file name ending with the.java extension indicates that the file contains Java source code. ◦ Eclipse (www.eclipse.org), ◦ NetBeans (www.netbeans.org),www.netbeans.org ◦ JBuilder (www.borland.com), ◦ JCreator (www.jcreator.com), ◦ BlueJ (www.blueJ.org),www.blueJ.org ◦ jGRASP (www.jgrasp.org) ◦ jEdit (www.jedit.org). 9:17 AM

10. Phase 2: Compiling a Java Program into Bytecodes the programmer uses the command javac (the Java compiler) to compile a program. For example, to compile a program called Welcome.java, you would type javac Welcome.java If the program compiles, the compiler produces a.class file called Welcome.class that contains the compiled version of the program. The Java compiler translates Java source code into bytecodes that represent the tasks to execute in the execution phase (Phase 5). Bytecodes are executed by the Java Virtual Machine (JVM)—a part of the JDK and the foundation of the Java platform. A virtual machine (VM) is a software application that simulates a computer, but hides the under- lying operating system and hardware from the programs that interact with the VM. the same VM is implemented on many computer platforms, applications that it executes can be used on all those platforms. bytecodes are platform-independent instructions—they are not dependent on a particular hardware platform (>< machine codes). ->So Java’s bytecodes are portable—that is, the same bytecodes can execute on any platform containing a JVM that understands the version of Java in which the bytecodes were compiled. The JVM is invoked by the java command. 9:17 AM

11. Phase 3: Loading a Program into Memory the program must be placed in memory before it can execute—known as loading. java Welcome The class loader takes the.class files containing the program’s bytecodes and transfers them to primary memory. The class loader also loads any of the.class files provided by Java that your program uses. The.class files can be loaded from a disk on your system or over a network (e.g., your local college or company network, or the Internet). 9:17 AM

12. Phase 4: Bytecode Verification as the classes are loaded, the bytecode verifier examines their bytecodes to ensure that they are valid and do not violate Java’s security restrictions. Java enforces strong security, to make sure that Java programs arriving over the network do not damage your files or your system (as computer viruses and worms might). 9:17 AM

13. Phase 5: Execution the JVM executes the program’s bytecodes, thus performing the actions specified by the program. In early Java versions, the JVM was simply an interpreter for Java bytecodes -> execute slowly. Today’s JVMs typically execute bytecodes using a combination of interpretation and so-called just- in-time (JIT) compilation. Thus Java programs actually go through two compilation phases— one in which source code is translated into bytecodes (for portability across JVMs on different computer platforms) and a second in which, during execution, the bytecodes are translated into machine language for the actual computer on which the program executes. 9:17 AM

14. Compiling and executing the Java program The java compiler creates a file called 'First.class' that contains the byte codes To actually run the program, a java interpreter called java is required to execute the code. 9:17 AM

15. Passing Command Line Arguments class CommLineArg { public static void main (String [] pargs) { System.out.println("These are the arguments passed to the main method."); System.out.println(pargs [0]); System.out.println(pargs [1]); System.out.println(pargs [2]); } 9:17 AM

16. Passing Command Line Arguments Output 9:17 AM

17. Basics of the Java Language Classes & Methods Data types Variables Constants Operators Control structures 9:17 AM

18. Classes in Java Class declaration Syntax class Classname { var_datatype variablename; : met_datatype methodname(parameter_list) : } 9:17 AM

19. Sample class 9:17 AM

20. Data Types byte char boolean short int long float double Array Class Interface 9:17 AM

21. Integer Types The integer types are for numbers without fractional parts. Negative values are allowed. 9:17 AM

22. Floating-Point Types The floating-point types denote numbers with fractional parts 9:17 AM

23. The char Type The char type is used to describe individual characters. For example, 'A' is a character constant with value 65. It is different from "A", a string containing a single character. Unicode code units can be expressed as hexadecimal values that run from \u0000 to \uFFFF. For example, \u2122 is the trademark symbol (™) and \u03C0 is the Greek letter pi (π). 9:17 AM

24. The boolean Type The boolean type has two values, false and true. It is used for evaluating logical conditions. You cannot convert between integers and boolean values. void bubbleSort(int[] x, int n) { boolean anotherPass; // true if something was out of order do { anotherPass = false; // assume everything sorted for (int i=0; i<n-1; i++) { if (x[i] > x[i+1]) { int temp = x[i]; x[i] = x[i+1]; x[i+1] = temp; // exchange anotherPass = true; // something wasn't sorted, keep going } } while (anotherPass); } void bubbleSort(int[] x, int n) { boolean anotherPass; // true if something was out of order do { anotherPass = false; // assume everything sorted for (int i=0; i<n-1; i++) { if (x[i] > x[i+1]) { int temp = x[i]; x[i] = x[i+1]; x[i+1] = temp; // exchange anotherPass = true; // something wasn't sorted, keep going } } while (anotherPass); } 9:17 AM

25. Type Casting In type casting, a data type is converted into another data type. Example float c = 34.89675f; int b = (int)c + 10; 9:17 AM

26. Automatic type and Casting There are two type of data conversion: automatic type conversion and casting. When one type of data is assigned to a variable of another type then automatic type conversion takes place provided it meets the conditions specified: ◦ The two types are compatible ◦ The destination type is larger than the source type. Casting is used for explicit type conversion. It loses information above the magnitude of the value being converted. 9:17 AM

27. Type Promotion Rules All byte and short values are promoted to int type. If one operand is long, the whole expression is promoted to long. If one operand is float then the whole expression is promoted to float. If one operand is double then the whole expression is promoted to double. 9:17 AM

29. Variables Three components of a variable declaration are: ◦ Data type ◦ Name ◦ Initial value to be assigned (optional) Syntax datatype identifier [=value][, identifier[=value]...]; 9:17 AM

30. Initializing Variables you must explicitly initialize it by means of an assignment statement—you can never use the values of uninitialized variables. the Java compiler flags the following sequence of statements as an error: int vacationDays; System.out.println(vacationDays); // ERROR--variable not initialized in Java you can put declarations anywhere in your code. double salary = 65000.0; System.out.println(salary); int vacationDays = 12; // ok to declare a variable here 9:17 AM

31. Example Output class DynVar { public static void main(String [] args) { double len = 5.0, wide = 7.0; double num = Math.sqrt(len * len + wide * wide); System.out.println("Value of num after dynamic initialization is " + num); } 9:17 AM

32. Scope and Lifetime of Variables Variables can be declared inside a block. The block begins with an opening curly brace and ends with a closing curly brace. A block defines a scope. A new scope is created every time a new block is created. Scope specifies what objects are visible to other parts of the program. It also determines the life of an object. 9:17 AM

33. Example class ScopeVar { public static void main(String [] args) { int num = 10; if ( num == 10) { // num is available in inner scope int num1 = num * num; System.out.println("Value of num and num1 are " + num + " " + num1); } //num1 = 10; System.out.println("Value of num is " + num); } Output 9:17 AM

34. Constants use the keyword final to denote a constant. public class Constants { public static void main(String[] args) { final double CM_PER_INCH = 2.54; double paperWidth = 8.5; double paperHeight = 11; System.out.println("Paper size in centimeters: " + paperWidth * CM_PER_INCH + " by " + paperHeight * CM_PER_INCH); } } The keyword final indicates that you can assign to the variable once, and then its value is set once and for all. It is customary to name constants in all uppercase. 9:17 AM

35. Constants It is probably more common in Java to want a constant that is available to multiple methods inside a single class. These are usually called class constants. You set up a class constant with the keywords static final. Note that the definition of the class constant appears outside the main method. Thus, the constant can also be used in other methods of the same class. public class Constants2 { public static void main(String[] args) { double paperWidth = 8.5; double paperHeight = 11; System.out.println("Paper size in centimeters: “ + paperWidth * CM_PER_INCH + " by " + paperHeight * CM_PER_INCH); } public static final double CM_PER_INCH = 2.54; } 9:17 AM

36. Array Declarations Three ways to declare an array are: ◦ datatype identifier [ ]; ◦ datatype identifier [ ] = new datatype[size]; ◦ datatype identifier [ ] = {value1,value2,….valueN}; 9:17 AM

37. Example – One Dimensional Array class ArrDemo { public static void main(String [] arg) { double nums[] = {10.1, 11.3, 12.5,13.7, 14.9}; System.out.println(" The value at location 3 is : " + nums[3]); } Output 9:17 AM

38. Example – Multi Dimensional Array class MultiArrayDemo { public static void main ( String [] arg) { int multi[][] = new int [4][]; multi[0] = new int[4]; multi[1] = new int[4]; multi[2] = new int[4]; multi[3] = new int[4]; int num = 0; for (int count = 0; count < 4; count++) { for (int ctr = 0; ctr < count+1; ctr++) { multi[count][ctr] = num; num++; } for (int count = 0; count < 4; count++) { for (int ctr = 0; ctr < count+1; ctr++) { System.out.print(multi[count][ctr] + " "); System.out.println(); } Output 9:17 AM

39. Operators Arithmetic Operators Bitwise Operators Relational Operators Logical Operators Conditional Operators Assignment operators 9:17 AM

40. Arithmetic Operators Operands of the arithmetic operators must be of numeric type. Boolean operands cannot be used, but character operands are allowed. These operators are used in mathematical expressions. 9:17 AM

41. Example class ArithmeticOp { public static void main ( String [] arg) { int num = 5, num1 = 12, num2 = 20, result; result = num + num1; System.out.println("Sum of num and num1 is : (num + num1) " + result); result = num % num1; System.out.println("Modulus of num and num1 is : (num % num1) " + result); result *= num2; System.out.println("Product of result and num2 is : (result *= num2) " + result); System.out.println("Value of num before the operation is : " + num); num ++; System.out.println("Value of num after ++ operation is : " + num); double num3 = 25.75, num4 = 14.25, res; res = num3 - num4; System.out.println("num3 – num4 is : " +res); res -= 2.50; System.out.println("res -= 2.50 " + res); System.out.println("Value of res before -- operation is : "+ res); res--; System.out.println("Value of res after -- operation is : " + res); } 9:17 AM

42. Output 9:17 AM

43. Bitwise Operators A bitwise operator allows manipulation of individual bits in an integral primitive data type. These operators act upon the individual bits of their operands. Bitwise operators perform Boolean algebra on the corresponding bits in the two arguments to produce the result. 9:17 AM

44. The bitwise operators are & (“and”) | (“or”) ^ (“xor”) ~ (“not”) These operators work on bit patterns. For example, if n is an integer variable, then int fourthBitFromRight = (n & 8) / 8; gives you a 1 if the fourth bit from the right in the binary representation of n is 1, and 0 if not. Using & with the appropriate power of 2 lets you mask out all but a single bit. 9:17 AM

45. Relational Operators Relational operators test the relation between two operands. The result of an expression in which relational operators are used, is Boolean (either true or false). Relational operators are used in control structures. 9:17 AM

46. Example class RelOp { public static void main(String [] args) { float num = 10.0F; double num1 = 10.0; if (num == num1) System.out.println ("num is equal to num1"); else System.out.println ("num is not equal to num1"); } Output 9:17 AM

47. Logical Operators Logical operators work with Boolean operands. Some operators are ◦&◦& ◦|◦| ◦^◦^ ◦!◦! 9:17 AM

48. Conditional Operators The conditional operator is unique, because it is a ternary or triadic operator that has three operands to the expression. It can replace certain types of if-then-else statements. The code below checks whether a commuter’s age is greater than 65 and print the message. CommuterCategory = (CommuterAge > 65)? “Senior Citizen” : “Regular”; 9:17 AM

49. Assignment Operators The assignment operator is a single equal sign, =, and assigns a value to a variable. Assigning values to more than one variable can be done at a time. In other words, it allows us to create a chain of assignments. 9:17 AM

50. Operator Precedence Parentheses: ( ) and [ ] Unary Operators: +, -, ++, --, ~, ! Arithmetic and Shift operators: *, /, %, +, -, >>, << Relational Operators: >, >=, <, <=, ==, != Logical and Bitwise Operators: &, ^, |, &&, ||, Conditional and Assignment Operators: ?=, =, *=, /=, +=, - = Parentheses are used to change the order in which an expression is evaluated. Any part of an expression enclosed in parentheses is evaluated first. 9:17 AM

51. Mathematical Functions and Constants The Math class contains an assortment of mathematical functions that you may occasionally need, depending on the kind of programming that you do. To take the square root of a number, use the sqrt method: double x = 4; double y = Math.sqrt(x); System.out.println(y); // prints 2.0 The Java programming language has no operator for raising a quantity to a power. You must use the pow method in the Math class. double y = Math.pow(x, a); Math.PI Math.E 9:17 AM

52. Formatting output with Escape Sequences Whenever an output is to be displayed on the screen, it needs to be formatted. The formatting can be done with the help of escape sequences that Java provides. System.out.println (“Happy \tBirthday ”); ◦ Output: HappyBirthday 9:17 AM

53. Control Flow All application development environments provide a decision making process called control flow statements that direct the application execution. Flow control enables a developer to create an application that can examine the existing conditions, and decide a suitable course of action. Loops or iteration are an important programming construct that can be used to repeatedly execute a set of actions. Jump statements allow the program to execute in a non-linear fashion. 9:17 AM

54. Control Flow Structures in Java Decision-making ◦ if-else statement ◦ switch-case statement Loops ◦ while loop ◦ do-while loop ◦ for loop 9:17 AM

55. if-else statement The if-else statement tests the result of a condition, and performs appropriate actions based on the result. It can be used to route program execution through two different paths. The format of an if-else statement is very simple and is given below: if (condition) { action1; } else { action2; } 9:17 AM

56. Example class CheckNum { public static void main(String [] args) { int num = 10; if (num % 2 == 0) System.out.println(num + " is an even number"); else System.out.println(num + " is an odd number"); } Output 9:17 AM

57. switch – case statement The switch – case statement can be used in place of if-else-if statement. It is used in situations where the expression being evaluated results in multiple values. The use of the switch-case statement leads to simpler code, and better performance. 9:17 AM

58. Example class SwitchDemo { public static void main(String[] args) { int day = 4; String str; switch (day) { case 0: str = "Sunday"; break; case 1: str = "Monday"; break; case 2: str = "Tuesday"; break; case 3: str = "Wednesday"; break; case 4: str = "Thursday"; break; case 5: str = "Friday"; break; case 6: str = "Saturday"; break; default: str = "Invalid day"; } System.out.println(str); } Output 9:17 AM

59. while Loop while loops are used for situations when a loop has to be executed as long as certain condition is True. The number of times a loop is to be executed is not pre-determined, but depends on the condition. The syntax is: while (condition) { action statements;... } 9:17 AM

60. Example class FactDemo { public static void main(String [] args) { int num = 5, fact = 1; while (num >= 1) { fact *= num; num--; } System.out.println("The factorial of 5 is : " + fact); } Output 9:17 AM

61. do – while Loop The do-while loop executes certain statements till the specified condition is True. These loops are similar to the while loops, except that a do-while loop executes at least once, even if the specified condition is False. The syntax is: do { action statements;.. } while (condition); 9:17 AM

62. Example class DoWhileDemo { public static void main(String [] args) { int count = 1, sum = 0; do { sum += count; count++; }while (count <= 100); System.out.println("The sum of first 100 numbers is : " + sum); } The sum of first 100 numbers is : 5050 Output 9:17 AM

63. for Loop All loops have some common features: a counter variable that is initialized before the loop begins, a condition that tests the counter variable and a statement that modifies the value of the counter variable. The for loop provides a compact format for incorporating these features. Syntax: for (initialization statements; condition; increment / decrement statements) { action statements;.. } 9:17 AM

64. Example class ForDemo { public static void main(String [] args) { int count = 1, sum = 0; for (count = 1; count <= 10; count += 2) { sum += count; } System.out.println("The sum of first 5 odd numbers is : " + sum); } The sum of first 5 odd numbers is : 25 Output 9:17 AM

65. Jump Statements Three jump statements are: ◦ break ◦ continue ◦ return The three uses of break statements are: ◦ It terminates a statement sequence in a switch statement. ◦ It can be used to exit a loop. ◦ It is another form of goto. 9:17 AM

66. Example class BrDemoAppl { public static void main(String [] args) { for (int count = 1; count <= 100; count++) { if (count == 10) break; System.out.println("The value of num is : " + count); } System.out.println("The loop is over"); } The value of num is : 1 The value of num is : 2 The value of num is : 3 The value of num is : 4 The value of num is : 5 The value of num is : 6 The value of num is : 7 The value of num is : 8 The value of num is : 9 The loop is over Output 9:17 AM

67. Summary A Java program consists of a set of classes. A program may contain comments. The compiler ignores this commented lines. The Java program must have a main() method from where it begins its execution. Classes define a template for units that store data and code related to an entity. Variables defined in a class are called the instance variables. There are two types of casting:widening and narrowing casting. Variables are basic unit of storage. Each variable has a scope and lifetime. Arrays are used to store several items of same data type in consecutive memory locations. 9:17 AM

68. Summary Contd… Java provides different types of operators. They include: ◦ Arithmetic ◦ Bitwise ◦ Relational ◦ Logical ◦ Conditional ◦ Assignment Java supports the following programming constructs: ◦ if-else ◦ switch ◦ for ◦ while ◦ do-while The three jump statements-break,continue and return helps to transfer control to another part of the program. 9:17 AM