a basic java programming and data type.ppt

PROGRAMMING WITH JAVA Instructor : Neelima Gupta

INTRODUCTION TO JAVA  What Is Java?  Getting Started With Java Programming – Create, Compile and Running a Java Application 2

CHARACTERISTICS OF JAVA  Java is simple  Java is object-oriented  Java is distributed  Java is interpreted  Java is robust  Java is secure  Java is architecture-neutral  Java is portable  Java’s performance  Java is multithreaded  Java is dynamic 3

GETTING STARTED WITH JAVA PROGRAMMING A Simple Java Application Compiling Programs Executing Applications 4

A SIMPLE APPLICATION Example 1.1 //This application program prints Welcome //to Java! package chapter1; public class Welcome { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } 5

ANATOMY OF A JAVA PROGRAM  Comments  Reserved words  Modifiers  Statements  Blocks  Classes  Methods  The main method  The exit method 6

COMMENTS In Java, comments are preceded by two slashes (//) in a line, or enclosed between /* and */ in one or multiple lines. When the compiler sees //, it ignores all text after // in the same line. When it sees /*, it scans for the next */ and ignores any text between /* and */. 7

RESERVED WORDS Reserved words or keywords are words that have a specific meaning to the compiler and cannot be used for other purposes in the program. For example, when the compiler sees the word class, it understands that the word after class is the name for the class. Other reserved words in Example 1.1 are public, static, and void. Their use will be introduced later. 8

MODIFIERS Java uses certain reserved words called modifiers that specify the properties of the data, methods, and classes and how they can be used. Examples of modifiers are public and static. Other modifiers are private, final, abstract, and protected. A public datum, method, or class can be accessed by other programs. A private datum or method cannot be accessed by other programs. 9

STATEMENTS A statement represents an action or a sequence of actions. The statement System.out.println("Welcome to Java!"); in the program in Example 1.1 is a statement to display the greeting "Welcome to Java!" Every statement in Java ends with a semicolon (;). 10

BLOCKS 11 A pair of braces in a program forms a block that groups components of a program. public class Test { public static void main(String[] args) { System.out.println("Welcome to Java!"); } } Class block Method block

CLASSES The class is the essential Java construct. A class is a template or blueprint for objects. A java program is defined by using one or more classes. 12

METHODS What is System.out.println? It is a method: a collection of statements that performs a sequence of operations to display a message on the console.  It can be used even without fully understanding the details of how it works. It is used by invoking a statement with a string argument. The string argument is enclosed within parentheses. In this case, the argument is "Welcome to Java!" You can call the same println method with a different argument to print a different message. 13

MAIN METHOD The main method provides the control of program flow. The Java interpreter executes the application by invoking the main method. The main method looks like this: public static void main(String[] args) { // Statements; } 14

THE EXIT METHOD Use Exit to terminate the program and stop all threads. When your program starts, a thread is spawned to run the program. To terminate the thread, you have to invoke the exit method. 15

PRIMITIVE DATA TYPES AND OPERATIONS  Introduce Programming with an Example  Identifiers, Variables, and Constants  Primitive Data Types – byte, short, int, long, float, double, char, boolean  Expressions  Operators, Precedence, Associativity, Operand Evaluation Order: ++, --, *, /, %, +=, -=, *=, /=, %=, ^, &, |, +, -,  Getting Input from Input Dialog Boxes  Case Studies (Computing Mortgage, and Computing Changes)  Style and Documentation Guidelines  Syntax Errors, Runtime Errors, and Logic Errors 16

IDENTIFIERS  An identifier is a sequence of characters that consist of letters, digits, underscores (_), and dollar signs ($).  An identifier must start with a letter, an underscore (_), or a dollar sign ($). It cannot start with a digit.  An identifier cannot be a reserved word. (See Appendix A, “Java Keywords,” for a list of reserved words).  An identifier cannot be true, false, or null.  An identifier can be of any length. 17

VARIABLES // Compute the first area radius = 1.0; area = radius*radius*3.14159; System.out.println("The area is “ + area + " for radius "+radius); // Compute the second area radius = 2.0; area = radius*radius*3.14159; System.out.println("The area is “ + area + " for radius "+radius); 18

DECLARING VARIABLES int x; // Declare x to be an // integer variable; double radius; // Declare radius to // be a double variable; char a; // Declare a to be a // character variable; 19

NUMERICAL DATA TYPES (P.33) byte 8 bits short 16 bits int 32 bits long 64 bits float 32 bits double 64 bits 20

ASSIGNMENT STATEMENTS x = 1; // Assign 1 to x; radius = 1.0; // Assign 1.0 to radius; a = 'A'; // Assign 'A' to a; 21

DECLARING AND INITIALIZING IN ONE STEP  int x = 1;  double d = 1.4;  float f = 1.4; Is this statement correct? 22

CONSTANTS final datatype CONSTANTNAME = VALUE; final double PI = 3.14159; final int SIZE = 3; 23

OPERATORS +, -, *, /, and % 5/2 yields an integer 2. 5.0/2 yields a double value 2.5 5 % 2 yields 1 (the remainder of the division) 5.0 % 2 is not defined : modulo is defined only for integers. 24

NOTE Calculations involving floating-point numbers are approximated because these numbers are not stored with complete accuracy. For example, System.out.println(1 - 0.1 - 0.1 - 0.1 - 0.1 - 0.1); displays 0.5000000000000001, not 0.5, and System.out.println(1.0 - 0.9); displays 0.09999999999999998, not 0.1. Integers are stored precisely. Therefore, calculations with integers yield a precise integer result. 25

EXAMPLE PROGRAM 1: ADDITION 26 public class addition { public static void main(String[] args) { // declare variables int x, y, z; // Specify values of x and y x = 2; y = 3; z = x + y; System.out.println("x has a value of " + x); System.out.println("y has a value of " + y); System.out.println("The sum of x + y is " + z); System.exit(0); } }

EXAMPLE PROGRAM 2 : DIVISION 27 public class division { public static void main ( String[] args) { //declare variables int x, y, z ; x = 12; y = 4; z = x / y ; System.out.println("x has a value of " + x); System.out.println("y has a value of " + y); System.out.println("x divided by y is " + z); System.exit(0); } }

DOWNLOAD JAVA  From www.java.sun.com/j2se  Click on j2se 5.0  See on your right (popular downloads) ..click on j2se 5.0  Click on download jdk 5.0 update 3  Accept the agreement and continue  Download the version as per your platform  For example, for Windows click on Windows offline installation – this will download the required file .. This will take a lot of time .. depending upon the speed of your line .. Once downloaded ..run this file to install Java 28

COMPILING AND RUNNING A JAVA PROGRAM  Java source code files (files with a .java extension) are compiled into a format called bytecode (files with a .class extension), which can then be executed by a Java interpreter. Compiled Java code can run on most computers because Java interpreters and runtime environments, known as Java Virtual Machines (VMs), exist for most operating systems, including UNIX, the MACintosh OS, and Windows. Bytecode can also be converted directly into machine language instructions by a just-in-time compiler (JIT). 29

FOR EXAMPLE  Create a file named say .. addition.java using some editor say wordpad.  From the command line type the following – javac addition.java (java code compiled to a bytecode)  A file called addition.class(bytecode) is created,  Now type java addition (bytecode being executed by java interpreter) And you will get the results 30

NUMBER LITERALS A literal is a constant value that appears directly in the program. For example, 34, 1,000,000, and 5.0 are literals in the following statements: int i = 34; long l = 1000000; double d = 5.0; 31

INTEGER LITERALS An integer literal can be assigned to an integer variable as long as it can fit into the variable. A compilation error would occur if the literal were too large for the variable to hold. For example, the statement byte b = 1000 would cause a compilation error, because 1000 cannot be stored in a variable of the byte type. An integer literal is assumed to be of the int type, whose value is between -231 (- 2147483648) to 231–1 (2147483647). To denote an integer literal of the long type, append it with the letter L or l. L is preferred because l (lowercase L) can easily be confused with 1 (the digit one). 32

FLOATING-POINT LITERALS Floating-point literals are written with a decimal point. By default, a floating-point literal is treated as a double type value. For example, 5.0 is considered a double value, not a float value. You can make a number a float by appending the letter f or F, and make a number a double by appending the letter d or D. For example, you can use 100.2f or 100.2F for a float number, and 100.2d or 100.2D for a double number. 33

SCIENTIFIC NOTATION Floating-point literals can also be specified in scientific notation, for example, 1.23456e+2, same as 1.23456e2, is equivalent to 123.456, and 1.23456e-2 is equivalent to 0.0123456. E (or e) represents an exponent and it can be either in lowercase or uppercase. 34

ARITHMETIC EXPRESSIONS 35 ) 9 4 ( 9 ) )( 5 ( 10 5 4 3 y x x x c b a y x         is translated to (3+4*x)/5 – 10*(y-5)*(a+b+c)/x + 9*(4/x + (9+x)/y)

SHORTCUT ASSIGNMENT OPERATORS 36 Operator Example Equivalent += i+=8 i = i+8 -= f-=8.0 f = f-8.0 *= i*=8 i = i*8 /= i/=8 i = i/8 %= i%=8 i = i%8

INCREMENT AND DECREMENT OPERATORS 37 x++; // Same as x = x + 1; ++x; // Same as x = x + 1; x––; // Same as x = x - 1; ––x; // Same as x = x - 1; suffix prefix suffix prefix

INCREMENT AND DECREMENT OPERATORS, CONT. 38 int i=10; int newNum = 10*i++; int newNum = 10*i; i = i + 1; Equivalent to int i=10; int newNum = 10*(++i); i = i + 1; int newNum = 10*i; Equivalent to

INCREMENT AND DECREMENT OPERATORS, CONT. 39 Using increment and decrement operators makes expressions short, but it also makes them complex and difficult to read. Avoid using these operators in expressions that modify multiple variables, or the same variable for multiple times such as this: int k = ++i + i. Its not a good programming

40 public class assignment_operators { public static void main(String[] args) { // declare variables int x = 10; int y = 5; int z = 3; System.out.println("x = "+x+", y = "+y+", z = "+z); x++; // x = x+1; y += x; // y = y+x; z *= x; // z = z*x; System.out.println("Now x = "+x+", y = "+y+", z = "+z); x--; // x = x-1; y *= x; // y = y*x; z %= x; // z = z%x; System.out.println("And now x = "+x+", y = "+y+", z = "+z); System.exit(0); } }

41 public class circle_area { public static void main(String[] args) { // declare variables double radius, area; // assign radius of the circle radius = 3.00; area = radius * radius * 3.14159 ; System.out.println("The area of the circle of radius " + radius + " is " + area); System.exit(0); } }

42 public class circle_area_pi { public static void main(String[] args) { final double PI = 3.14159; // declare variables double radius, area; // assign radius of the circle radius = 3.00; area = radius * radius * PI ; System.out.println("The area of the circle of radius " + radius + " is " + area); System.exit(0); } }

ASSIGNMENT EXPRESSIONS AND ASSIGNMENT STATEMENTS Prior to Java 2, all the expressions can be used as statements. Since Java 2, only the following types of expressions can be statements: variable op= expression; // Where op is +, -, *, /, or % ++variable; variable++; --variable; variable--; 43

NUMERIC TYPE CONVERSION Consider the following statements: byte i = 100; long k = i*3+4; double d = i*3.1+k/2; int x = k; //(Wrong) long k = x; //(fine,implicit casting) 44

TYPE CASTING  double  float  long  int  short  byte 45

TYPE CASTING, CONT. Implicit casting double d = 3; (type widening) Explicit casting int i = (int)3.0; (type narrowing) What is wrong? int x = 5/2.0; 46

ANSWER  Needs explicit type cast  int x = (int) 5/2.0; 47

CHARACTER DATA TYPE char letter = 'A'; (ASCII) char numChar = '4'; (ASCII) char letter = 'u0041'; (Unicode) char numChar = 'u0034'; (Unicode) Special characters char tab = ‘t’; 48

UNICODE FORMAT 49 Description Escape Sequence Unicode Backspace b u0008 Tab t u0009 Linefeed n u000a Carriage return r u000d

APPENDIX B: ASCII CHARACTER SET 50 ASCII Character Set is a subset of the Unicode from u0000 to u007f

ASCII CHARACTER SET, CONT. 51 ASCII Character Set is a subset of the Unicode from u0000 to u007f

CASTING BETWEEN CHAR AND NUMERIC TYPES 52 int i = 'a'; // Same as int i = (int)'a'; char c = 97; // Same as char c = (char)97;

THE BOOLEAN TYPE AND OPERATORS boolean lightsOn = true; boolean lightsOn = false; boolean b = (1 > 2);  && (and) (1 < x) && (x < 100)  || (or) (lightsOn) || (isDayTime)  ! (not) !(isStopped) 53

COMPARISON OPERATORS 54 Operator Name < less than <= less than or equal to > greater than >= greater than or equal to == equal to != not equal to

BOOLEAN OPERATORS 55 Operator Name ! not && and || or ^ exclusive or

TRUTH TABLE FOR OPERATOR ! 56 Truth Table for Operator ! Operand !Operand true false false true

TRUTH TABLE FOR OPERATOR && 57 Operand1 Operand2 Operand1 && Operand2 false false false false true false true false false true true true

TRUTH TABLE FOR OPERATOR || 58 Operand1 Operand2 Operand1 || Operand2 false false false false true true true false true true true true

OPERATOR PRECEDENCE How to evaluate 3 + 4 * 4 > 5 * (4 + 3) - ++i 59

OPERATOR PRECEDENCE  var++, var--  +, - (Unary plus and minus), ++var,--var  (type) Casting  ! (Not)  *, /, % (Multiplication, division, and modulus)  +, - (Binary addition and subtraction)  <, <=, >, >= (Comparison)  ==, !=; (Equality)  & (Unconditional AND)  ^ (Exclusive OR)  | (Unconditional OR)  && (Conditional AND) Short-circuit AND  || (Conditional OR) Short-circuit OR  =, +=, -=, *=, /=, %= (Assignment operator) 60

OPERATOR ASSOCIATIVITY When two operators with the same precedence are evaluated, the associativity of the operators determines the order of evaluation. All binary operators except assignment operators are left-associative. a – b + c – d is equivalent to ((a – b) + c) – d Assignment operators are right- associative. Therefore, the expression a = b += c = 5 is equivalent to a = (b += (c = 5)) 61

OPERAND EVALUATION ORDER The precedence and associativity rules specify the order of the operators, but do not specify the order in which the operands of a binary operator are evaluated. Operands are evaluated from left to right in Java. The left-hand operand of a binary operator is evaluated before any part of the right- hand operand is evaluated. 62

OPERAND EVALUATION ORDER, CONT. If no operands have side effects that change the value of a variable, the order of operand evaluation is irrelevant. Interesting cases arise when operands do have a side effect. For example, x becomes 1 in the following code, because a is evaluated to 0 before ++a is evaluated to 1. int a = 0; int x = a + (++a); But x becomes 2 in the following code, because ++a is evaluated to 1, then a is evaluated to 1. int a = 0; int x = ++a + a; 63

OPERATOR PRECEDENCE How to evaluate 3 + 4 * 4 > 5 * (4 + 3) - ++i Lets parenthisize (3 + (4 * 4) ) > ( (5 * (4 + 3)) – (++i ) ) This is evaluates to 19 > (35 – (++i)) This evaluates to true if the value of i just before this expression is > 15 64

GETTING INPUT FROM INPUT DIALOG BOXES String string = JOptionPane.showInputDialog( null, “Prompt Message”, “Dialog Title”, JOptionPane.QUESTION_MESSAGE)); where x is a string for the prompting message and y is a string for the title of the input dialog box. 65

CONVERTTING STRINGS TO INTEGERS The input returned from the input dialog box is a string. If you enter a numeric value such as 123, it returns “123”. To obtain the input as a number, you have to convert a string into a number. To convert a string into an int value, you can use the static parseInt method in the Integer class as follows: int intValue = Integer.parseInt(intString); where intString is a numeric string such as “123”. 66

CONVERTTING STRINGS TO DOUBLES To convert a string into a double value, you can use the static parseDouble method in the Double class as follows: double doubleValue =Double.parseDouble(doubleString); where doubleString is a numeric string such as “123.45”. 67

EXAMPLE 2.2 ENTERING INPUT FROM DIALOG BOXES 68 This program first prompts the user to enter a year as an int value and checks if it is a leap year, it then prompts you to enter a double value and checks if it is positive. A year is a leap year if it is divisible by 4 but not by 100, or it is divisible by 400.

EXAMPLE 2.4 COMPUTING CHANGES 69 This program lets the user enter the amount in decimal representing dollars and cents and output a report listing the monetary equivalent in single dollars, quarters, dimes, nickels, and pennies. Your program should report maximum number of dollars, then the maximum number of quarters, and so on, in this order.

PROGRAMMING STYLE AND DOCUMENTATION Appropriate Comments Naming Conventions Proper Indentation and Spacing Lines Block Styles 70

APPROPRIATE COMMENTS Include a summary at the beginning of the program to explain what the program does, its key features, its supporting data structures, and any unique techniques it uses. Include your name, class section, instruction, date, and a brief description at the beginning of the program. 71

NAMING CONVENTIONS  Choose meaningful and descriptive names.  Variables and method names: – Use lowercase. If the name consists of several words, concatenate all in one, use lowercase for the first word, and capitalize the first letter of each subsequent word in the name. For example, the variables radius and area, and the method computeArea. 72

NAMING CONVENTIONS, CONT.  Class names: – Capitalize the first letter of each word in the name. For example, the class name ComputeArea.  Constants: – Capitalize all letters in constants. For example, the constant PI. 73

PROPER INDENTATION AND SPACING  Indentation – Indent two spaces.  Spacing – Use blank line to separate segments of the code. 74

BLOCK STYLES Use end-of-line style for braces. 75 public class Test { public static void main(String[] args) { System.out.println("Block Styles"); } } public class Test { public static void main(String[] args) { System.out.println("Block Styles"); } } End-of-line style Next-line style

PROGRAMMING ERRORS  Syntax Errors – Detected by the compiler  Runtime Errors – Causes the program to abort  Logic Errors – Produces incorrect result 76

COMPILATION ERRORS public class ShowSyntaxErrors { public static void main(String[] args) { i = 30 System.out.println(i+4); } 77

RUNTIME ERRORS public class ShowRuntimeErrors { public static void main(String[] args) { int i = 1 / 0; } } 78

LOGIC ERRORS public class ShowLogicErrors { // Determine if a number is between 1 and 100 inclusively public static void main(String[] args) { // Prompt the user to enter a number String input = JOptionPane.showInputDialog(null, "Please enter an integer:", "ShowLogicErrors", JOptionPane.QUESTION_MESSAGE); int number = Integer.parseInt(input); // Display the result System.out.println("The number is between 1 and 100, " + "inclusively? " + ((1 < number) && (number < 100))); 79

a basic java programming and data type.ppt

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