Lesson 2 The Java Prog Lan AUBG ICoSCIS Team Assoc. Prof. Stoyan Bonev March, 23 - 24, 2013 SWU,...

Lesson 2The Java Prog Lan

AUBG ICoSCIS TeamAssoc. Prof. Stoyan Bonev

March, 23 - 24, 2013 SWU, Blagoevgrad

Time Schedule

March 23, Saturday - March 24, Sunday– 10:00 – 10:45 09:00 – 09:45– 11:00 – 11:45 10:00 – 10:45– 12:00 – 12:45 11:00 – 11:45

Lunch Break (45’) Lunch Break (45’)– 13:30 – 14:15 12:30 – 13:15– 14:30 – 15:15 13:30 – 14:15– 15:30 – 16:15 14:30 – 15:15

Lesson ContentsOverview of Java Programming Language Anatomy of a Java program

Sample source text Packages Comments Names – identifiers, reserved words, modifiers Classes – data fields, methods (statements, blocks of statements )

Components of a Java program Data – by category Data – by type Expressions (incl. operands & operators) Statements Routines (member functions - methods) I/O facilities Data collections – arrays

Demo programs - examples

4 4

The Basics of a Java ProgramJava program: collection of classes. Classes

capsulated as packages – named or unnamedPackage: collection of related classesClass: collection of data items and methods Method: designed to accomplish a specific taskThere is a main method public static void main()in every Java program. The main method provides the control of program flow. The JVM executes application by invoking the main method

5 5Java Programming: From Problem Analysis to Program Design, 4e

The package Logical entity describes user defined or API predefined package Really located as one file or as many files Syntax to mark package start: package <name>; Always first line in the source code May be omitted: program without explicit package name Reference to predefined package: import <package name>;import java.lang.*; This statement makes the methods in the library package java.lang available to the class following it.

java.lang is just 1 package in the Java library or API. Primitive data types and the class String:

Part of the Java language. They Don’t need to be imported

Java Programming: From Problem Analysis to Program Design, 3e 66Java Programming: From Problem Analysis to Program Design, 4e

Anatomy of a Java program: Sample source text

Sample Run:

05/05/23 Assoc. Prof. Stoyan Bonev

7

Comments

Line comment: A line comment is preceded by two slashes (//) in a line.Paragraph comment: A paragraph comment is enclosed between /* and */ in one or multiple lines.

javadoc comment: javadoc comments begin with /** and end with */. Used for documenting classes, data, methods. They can be extracted into HTML file using JDK's javadoc command.

Three types of comments in Java.

Java Programming: From Problem Analysis to Program Design, 3e 8

Names - Identifiers• Names of entities (like variables, named constants,

methods, classes, objects etc.) • 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. • An identifier can be of any length.• Java is case sensitive – ion, Ion, IOn, ION


Naming Conventions• Choose meaningful and descriptive names.• Class names:

– Capitalize the first letter of each word in the name. For example, the class name ComputeArea.

• Named Constants: – Capitalize all letters in constants, and use underscores to connect words.

For example, PI and MAX_VALUE

• 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.


Reserved WordsReserved 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, class, void. are reserved words.

ModifiersJava 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.


Data classified by Type

• Data Types Classified:

– 8 Primitive Data Types– boolean, byte, short, int, long, float, double, char

– Abstract/Reference Data Types (classes, objects)– String, Object, Frame, Person, Animal, …– Array types (also reference types)


Primitive Data Types – 3 subgroups

• Integral, which is a data type that deals with integers (or numbers without a decimal part) and characters

• char – Unicode – 2 bytes/char, to present symbolic data• byte, short, int, long, to present numeric data fixed point

• Floating-point, a data type that deals with decimal numbers• float: precision = 6 or 7 decimal places, Single (4 bytes)• double: precision = 15 decimal places, Double (8 bytes)

• Boolean, a data type that deals with logical values: true, false• Memory allocated to boolean data type is 1 bit


Values and Memory Allocation for Integral Data Types


Primitive Data Types

• Classified by Category as:• Literals• Named Constants• Variables


Literals (Constants)• Integer literals, integer constants, or integers:

23 -67 +4470177 0x1a

• Floating-point literals, floating-point constants, floating-point numbers: 12.34 +25.60 -3.15 5. .1663.14e-2 2.78e+3 5.23e4

• Character literals, character constants, or characters: 'a' '5' '+' '\n'


Named Constants• Named constant

– Cannot be changed during program execution– Declared by using the reserved word final– Initialized when it is declared

• Example:final double CENTIMETERS_PER_INCH = 2.54;final int NO_OF_STUDENTS = 20;final char BLANK = ' ';final double PAY_RATE = 15.75;


Variables• Variable (name, value, data type, size)

– Content may change during program execution– Must be declared before it can be used– May not be automatically initialized – If new value is assigned, old one is destroyed– Value can only be changed by an assignment statement

or an input (read) statement• Example: double amountDue;int counter;char ch;int num1, num2;


Declaring and Initializing Variables int first; OR int

first = 13; first = 13;

char ch; OR char ch = ‘E’; ch = ‘E’;

double value; OR double value = 35.68; value = 35.68;

-------------------------------------------------------------


Unicode FormatJava characters use Unicode, a 16-bit encoding scheme established by the Unicode Consortium to support the interchange, processing, and display of written texts in the world’s diverse languages. Unicode takes two bytes, preceded by \u, expressed in four hexadecimal numbers that run from '\u0000' to '\uFFFF'. So, Unicode can represent 65535 + 1 characters.

char letter = 'A'; (ASCII) char letter = '\u0041'; (Unicode)

char numChar = '4'; char numChar = '\u0034'; Unicode \u03b1 \u03b2 \u03b3 for three Greek letters


(Non-)Pointers in Java

• In Java, all primitive variables are value variables. (Real, actual)

– it is impossible to have a pointer to any variable of one of the primitive data types

• All object variables are actually reference variables (pointers, memory addresses) to objects.

– it is impossible to have anything but references to objects. You can never have a plain object variable


Expressions - operands

• Operands– Literals– Named Constants– Variables – regular(scalar) or indexed– Method call– Sub expression like ( … )


Arithmetic Operators and Operator Precedence

• 1. * / % (same precedence)• 2. + - (same precedence)

• Operators in 1 have a higher precedence than operators in 2

• When operators have the same level of precedence, operations are performed from left to right

• Unary operator: operator that has one operand• Binary operator: operator that has two operands


Mixed Arithmetic Expressions• Operands of different types• Examples2 + 3.56 / 4 + 3.9

• Integer operands yield an integer result; floating-point numbers yield floating-point results

• If both types of operands are present, the result is a floating-point number

• Precedence rules are followed


Type Conversion (Casting)

• Used to avoid implicit type coercion• Syntax(dataTypeName)expression

• Expression evaluated first, then type converted to dataTypeName

• Examples(int)(7.9 + 6.7) => 14(int)(7.9) + (int)(6.7) => 13


Conversion RulesWhen performing a binary operation involving two operands of different types, Java automatically converts the operand based on the following rules:

1. If one of the operands is double, the other is converted into

double.2. Otherwise, if one of the operands is float, the other is

converted into float.3. Otherwise, if one of the operands is long, the other is

converted into long.4. Otherwise, both operands are converted into int.


Type CastingImplicit casting double d = 3; (type widening permitted)

Explicit casting int i = (int)3.0; (type narrowing) int i = (int)3.9; (Fraction part is truncated) What is wrong? int x = 5 / 2.0;

byte, short, int, long, float, double

range increases


Comparison Operators

Operator Name

< less than

<= less than or equal to

> greater than

>= greater than or equal to

== equal to

!= not equal to

Logical Operators

Operator Name

! not

&& and

|| or

^ exclusive or

Conditional Operator

y = (x > 0) ? 1 : -1;


The class String

• Used to manipulate strings• String

– Sequence of zero or more characters– Enclosed in double quotation marks– Null or empty strings have no characters– Numeric strings consist of integers or decimal

numbers– Length is the number of characters in a string


Strings and the Operator +• Operator + can be used to concatenate two strings or

a string and a numeric value or character• Example

"The sum = " + 12 + 26-After this statement executes, the string assigned to str is:"The sum = 1226";

• Consider the following statement:"The sum = " + (12 + 26)

• In this statement, because of the parentheses, you first evaluate num1 + num2– Because num1 and num2 are both int variables, num1 + num2 = 12 + 26 = 38

– After this statement executes, the string assigned to str is:"The sum = 38";


Types of statements

• Declaration/definition statements

• Executable statements

• Every statement in Java ends with a semicolon (;).


BlocksA 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

Use end-of-line style for braces.


Executable Statements• Assignment stmts

– To implement linear algorithms• Selection/Decision stmts

– To implement branch algorithmsif, if-else, if-else if, switch

• Repetition/Iteration stmts – To implement loop algorithms for, while, do-

while, for(version foreach)• Input/Output

– Other break, continue


Assignment Statements

x = 1; // Assign 1 to x;

radius = 1.0; // Assign 1.0 to radius;a = 'A'; // Assign 'A' to a;variable = variable * (expression);is equivalent tovariable *= expression;Similarly,variable = variable + (expression);is equivalent tovariable += expression;


One-way if Statements

Boolean Expression

true

Statement(s)

false (radius >= 0)

true

area = radius * radius * PI; System.out.println("The area for the circle of " + "radius " + radius + " is " + area);

false

(A) (B)

if (boolean-expression) { statement(s);}

if (radius >= 0) { area = radius * radius * PI; System.out.println("The area" + " for the circle of radius " + radius + " is " + area);}

Java Programming: From Problem Analysis to Program Design, 3e 3512Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All

rights reserved. 0132130807

The Two-way if Statementif (boolean-expression) {

statement(s)-for-the-true-case;}else {

statement(s)-for-the-false-case;}

Boolean Expression

false true

Statement(s) for the false case Statement(s) for the true case


if...else Exampleif (radius >= 0) { area = radius * radius * 3.14159;

System.out.println("The area for the “ + “circle of radius " + radius + " is " + area);}else { System.out.println("Negative input");}


Switch-case

switch ( N ) { // (Assume N is an integer variable.) case 1: System.out.println("The number is 1."); break; case 2: case 4: case 8: System.out.println("The number is 2, 4, or 8."); System.out.println("(That's a power of 2!)"); break; case 3: case 6: case 9: System.out.println("The number is 3, 6, or 9."); System.out.println("(That's a multiple of 3!)"); break; case 5: System.out.println("The number is 5."); break; default: System.out.println("The number is 7 or is outside range 1 to 9.");}


44Liang, Introduction to Java Programming, Eighth Edition, (c) 2011 Pearson Education, Inc. All rights reserved. 0132130807

switch Statement Flow Chart

status is 0 Compute tax for single filers break

Compute tax for married file jointly break status is 1

Compute tax for married file separatly break status is 2

Compute tax for head of household break status is 3

Default actions default

Next Statement


Introducing while Loopsint count = 0;while (count < 100) { System.out.println("Welcome to Java"); count++;}


while Loop Flow Chartwhile (loop-continuation-condition) {

// loop-body;

Statement(s);

}

int count = 0;

while (count < 100) {

System.out.println("Welcome to Java!");

count++;

}

Loop Continuation Condition?

true

Statement(s) (loop body)

false (count < 100)?

true

System.out.println("Welcome to Java!"); count++;

false

(A) (B)

count = 0;



do-while Loop

do {

// Loop body;

Statement(s);

} while (loop-continuation-condition);


true

Statement(s) (loop body)

false



for Loopsfor (initial-action; loop-

continuation-condition; action-after-each-iteration) {

// loop body;Statement(s);

}

int i;for (i = 0; i < 100; i++) {System.out.println(

"Welcome to Java!"); }


true Statement(s) (loop body)

false

(A)

Action-After-Each-Iteration

Initial-Action

(i < 100)?

true System.out.println( "Welcome to Java");

false

(B)

i++

i = 0


For-loop

For (int i=1, j=10; i < j; i++, j-=2)

System.out.println("i="+i+" j="+j);

for (int i = 0; i < 4; i++){ for( char letter = 'A'; letter <= 'A' + i; letter++) System.out.print(letter); System.out.println();}

i=1 j=10i=2 j=8i=3 j=6

AABABCABCD


Enhanced for Loop (for-each loop)JDK 1.5 introduced a new for loop that enables you to traverse the complete array sequentially without using an index variable. For example, the following code displays all elements in the array myList:

for (double value: myList) System.out.println(value);

In general, the syntax is

for (elementType value: arrayRefVar) { // Process the value}

You still have to use an index variable if you wish to traverse the array in a different order or change the elements in the array.


Console Input (Read) statement

• Standard input stream object: System.in• Input numeric data to program

– Separate by blanks, lines, or tabs• To read data:

1. Create an input stream object of the class Scanner (import java.util.*; or import java.util.Scanner;)

2. Use the methods such as next(), nextLine(), nextInt(), nextFloat(), nextDouble()


Input (Read) statementstatic Scanner console = new Scanner(System.in);

• Java program:

static Scanner cin = new Scanner(System.in);int feet;int inches;

Suppose the input is: 23 7

Feet = cin.nextInt(); //Line 1Inches = cin.nextInt(); //Line 2

• How to read a single character:– char ch; ch = console.next().charAt(0);


Reading Input from the Console1. Create a Scanner object

Scanner cin = new Scanner(System.in);

2. Use the methods next(), nextByte(), nextShort(), nextInt(), nextLong(), nextFloat(), nextDouble(), or nextBoolean() to obtain to a string, byte, short, int, long, float, double, or boolean value. For example,

System.out.print("Enter a double value: ");Scanner cin = new Scanner(System.in);double d = cin.nextDouble();


public class CalculatingArea { public static void main(String[] args) { Scanner input = new Scanner(System.in);

System.out.println("This program calculates " +"the area of a rectangle or a triangle");

System.out.print("Enter a and b (for rectangle) " +"or a and h (for triangle): ");

int a = input.nextInt();int b = input.nextInt();System.out.print("Enter 1 for a rectangle or " +

"2 for a triangle: ");int choice = input.nextInt();double area = (double) (a * b) / choice;System.out.println("The area of your figure is " + area);}

}


Output (Write/Print/Display) statement

• Standard output object: System.out• Methods

printprintln

• SyntaxSystem.out.print(stringExp);System.out.println(stringExp);

System.out.println();


Input/Output using Dialog Boxes


JOptionPane InputTwo ways of obtaining input.

1. Using the Scanner class (console input) needs import java.util.Scanner;

2. Using JOptionPane input dialogs needs import javax.swing.JOptionPane;

51

Getting Input from Input Dialog Boxes String input = JOptionPane.showInputDialog( "Enter an input");

52

Converting Strings to IntegersThe 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”.

53

Converting 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”.

54

Displaying Text in a Message Dialog Box

Instead of using System.out.println() for console output

you can use the showMessageDialog method in the JOptionPane class. JOptionPane is one of the many predefined classes in the Java system, which can be reused rather than “reinventing the wheel.”

55

The showMessageDialog Method JOptionPane.showMessageDialog(null, "Welcome to Java!", "Display Message", JOptionPane.INFORMATION_MESSAGE);

DEMO program: Open file ProgDialogBoxes.java

56

Exercise on statementsWrite a Java program as a single class:• single method main() to include:

• program segment to calculate the greatest common divisor of two positive integer values

• program segment to calculate the factorial of a nonnegative integer value

• program segment to calculate the sum of integer numbers in range from n1…n2, such that n1<n2


Components of a Java programMethods & Classes

• To be discussed in lesson 3.


Data Collections

Typical popular Data collections:

• Arrays

Detailed discussion on arrays follows


59

Declaring and creating arrays

• Example for array objects:

int[] myArray; // declaration• This declares myArray to be an array reference variable• It does not create an array — it only provides a place to put a

reference of an array, i.e. address of an array.• Notice that the size is not part of the type

myArray = new int[10]; // creation• The new int[10] creates the array of size 10

• Write as

int[] myArray = new int[10]; // combined

Similar to C#


60

An array’s size is not part of its type

• When you declare an array, you declare its type; you must not specify its size– Example: String[] names;– or String names[];//not recommended

• When you create the array, you allocate space; you must specify its size– Example: names = new String[50];

• This is true even when the two are combined. Example:String[] names = new String[50];


61

Arrays of objects

• Suppose you declare and create an array of objects:– Person[] people = new Person[20];

• You have created an array named people, but you have not yet given values to each element in that array

• There is nothing wrong with this array, but– it has 20 references to Persons in it– all of these references are initially null– you have not yet defined 20 Persons– For example, people[12].name will give you a nullPointerException if you do not define the Persons.


62

Here’s one way to initialize an array of objects:

Person[] people = new Person[20];for (int i = 0; i < people.length; i++) { people[i] = new Person(“John");}

This approach has a slight drawback: all the array elements have similar values!

Remember: index of array elements starts at 0 and ends at (length – 1)


63

Resizing an array

The following is legal:

int[] myArray = new int[10];

...and later in the program,

myArray = new int[500]; // legal!

This is legal because the array’s size is not part of its type, but part of its value


64

Length of an array

• Arrays are objects.

• Every array has an instance constant, length, that tells how large the array is

• Example: for (int i = 0; i < scores.length; i++) System.out.println(scores[i]);

• Use of length is always preferred over using a literal constant such as 10

• Arrays have a length variable,• Strings have a length() method


65

• There is a special syntax for giving initial values to the elements of arrays

– This syntax can be used in place of new type[size]

– It can only be used in an array declaration

– The syntax is: { value, value, ..., value }

• Examples:

int[] primes = { 2,3,5,7,11,13,19};

String[] languages = { "Java","C","C++" };


66

Initializing arrays

• To initialize an array of Person: Person[] people = { new Person(“Elena"), new Person(“Ivan"), new Person(“Katya"), new Person(“Dimitar") };

• Notice that you do not specify the size of the array


67

Arrays - Recap

• Declare an array ref variable:– int[] counts; – String[] names; – int[][] matrix; //this is an array of arrays

• Create an array and assign its reference to array ref variable:– counts = new int[5]; – names = new String[100]; – matrix = new int[5][10];

• Use:– String months[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "July", "Aug", "Sep", "Oct", "Nov", "Dec"};

– for(int i = 0; i < months.length; i++) System.out.println("month: " + months[i]);


68

Array assignment

• Array assignment is object assignment:

• Object assignment does not copy values Person p1; Person p2; p1 = new Person(“Ivan"); p2 = p1; // p1 and p2 refer to same person (“point to”)

• Array assignment does not copy values int[] a1; int[] a2; a1 = new int[10]; a2 = a1; // a1 and a2 refer to the same array


69


Copying ArraysOften, in a program, you need to duplicate an array or a part of an array. In such cases you could attempt to use the assignment statement (=), as follows:

list2 = list1;

Contents of list1

list1

Contents of list2

list2

Before the assignment list2 = list1;

Contents of list1

list1

Contents of list2

list2

After the assignment list2 = list1;

Garbage


70

Copying ArraysUsing a loop:int[] srcArray = {2, 3, 1, 5, 10};int[] targetArray = new int[srcArray.length];

for (int i = 0; i < srcArrays.length; i++) targetArray[i] = srcArray[i];


71

Arrays of arrays

Arrays of arraysOr

Multi – Dimensional arrays


72

Arrays of arrays = Multidimensional arrays

• One-dimensional arrays are used to store linear collections of elements, i.e. vector.

• Two-dimensional arrays are used to store a matrix or a table.

• A two-dimensional array is one-dimensional array in which each element is another one-dimensional array. (look fwd after 7 slides)

• A multidimensional array is an array in which each element is another array


73

Arrays of arrays = Multidimensional arrays

• A three-dimensional array consists of an array of two-dimensional arrays, each of which is an array of one-dimensional arrays.

int[][][] x = new int[2][2][5];• x[0] and x[1] are two-dimensional arrays.• x[0][0], x[0][1], x[1][0], x[1][1] are

one-dimensional arrays and each contains 5 elements• x.length is 2• x[0].length and x[1].length are 2• x[0][0].length, x[0][1].length, x[1][0].length, x[1][1].length are 5


74

Arrays of arrays

• The elements of an array can be arrays.

• Declaration: int[][] table;

• Definition: table = new int[10][15];

• Combined: int[][] table = new int[10][15];

• The first index (10) is called the row index;• The second index (15) is the column index


75

Example array of arrays

• int[][] table = new int[3][2]; or,• int[][] table = { {1, 2}, {3, 6}, {7, 8} };

An array of three rows and two columns

1 23 67 8

0 10

12

• For example, table[1][1] contains 6• table[2][1] contains 8, and• table[1][2] is “array out of bounds”

• To “zero out this table”: for (int i = 0; i < 3; i++) for (int j = 0; j < 2; j++) table[i][j] = 0;


76

Declaring Variables of 2-D Arrays and Creating 2-D Arrays

// Declare array ref vardataType[][] refVar;

// Create array & assign its reference to variablerefVar = new dataType[10][10];

// Combine declaration and creation in one stmtdataType[][] refVar = new dataType[10][10];

// Alternative syntax, not recommendeddataType refVar[][] = new dataType[10][10];


77

Declaring Variables of 2-D Arrays and Creating 2-D Arrays

// declare array ref var, create 2D array and assign its reference to array ref var// all three above activities in one step - statement

int[][] matrix = new int[10][10]; matrix[0][0] = 3;

for (int i = 0; i < matrix.length; i++) for (int j = 0; j < matrix[i].length; j++) matrix[i][j] = (int)(Math.random() * 1000);

// matrix.length – numr of rows or matrix capacity// matrix[i].length – capacity of row nmr i


78


Two-dimensional Array Illustration

0 1 2 3 4 0

7

0 1 2 3 4

1 2 3 4

0 1 2 3 4 matrix[2][1] = 7;

matrix = new int[5][5];

3

7

0 1 2 0 1 2

int[][] array = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10, 11, 12} };

1

2

3

4

5

6

8

9

10

11

12

array.length? 4

array[0].length? 3

matrix.length? 5

matrix[0].length? 5


79


Lengths of Two-dimensional Arrays

x

x[0]

x[1]

x[2]

x[0][0] x[0][1] x[0][2] x[0][3] x[1][0] x[1][1] x[1][2] x[1][3] x[2][0] x[2][1] x[2][2] x[2][3]

x.length is 3

x[0].length is 4

x[1].length is 4

x[2].length is 4

int[][] x = new int[3][4];


80

Ragged ArraysEach row in a two-dimensional array is itself an array. So,

the rows can have different lengths. Such an array is known as a ragged array. For example,

int[][] matrix = { {1, 2, 3, 4, 5}, {2, 3, 4, 5}, {3, 4, 5}, {4, 5}, {5}};

matrix.length is 5 matrix[0].length is 5 matrix[1].length is 4 matrix[2].length is 3 matrix[3].length is 2 matrix[4].length is 1


81

Associative Arrays import java.util.Hashtable; … // associative array - special case – hashtable Hashtable<String, String> ht = new

Hashtable<String, String>();

ht.put("Sofia", "BG"); ht.put("Berlin", "DE");

System.out.print(" " + ht.get("Sofia"));


82

The ArrayList and Vector Classes You can create an array to store objects. But the array’s size is fixed once the array is created. Java provides the ArrayList class that can be used to store an unlimited number of objects.

java.util.ArrayList

+ArrayList() +add(o: Object) : void +add(index: int, o: Object) : void +clear(): void +contains(o: Object): boolean +get(index: int) : Object +indexOf(o: Object) : int +isEmpty(): boolean +lastIndexOf(o: Object) : int +remove(o: Object): boolean +size(): int +remove(index: int) : Object +set(index: int, o: Object) : Object

Appends a new element o at the end of this list. Adds a new element o at the specified index in this list. Removes all the elements from this list. Returns true if this list contains the element o. Returns the element from this list at the specified index. Returns the index of the first matching element in this list. Returns true if this list contains no elements. Returns the index of the last matching element in this list. Removes the element o from this list. Returns the number of elements in this list. Removes the element at the specified index. Sets the element at the specified index.

Creates an empty list.


83

ArrayList demo examplepackage sbarraylist;

import java.util.ArrayList;

public class SBArrayList {

public static void main(String[] args) {

ArrayList ar = new ArrayList();

ar.add("Sofia"); ar.add("Varna");

System.out.println(ar.toString());

for (int i=ar.size()-1; i>=0; i--) System.out.print(ar.get(i) +" ");

}

}


84

Practical tasks.


85

Initializing arrays with input values

java.util.Scanner input = new Scanner(System.in);System.out.println("Enter " + matrix.length + " rows and " + matrix[0].length + " columns: ");for (int row = 0; row < matrix.length; row++) { for (int column = 0; column < matrix[row].length; column++) { matrix[row][column] = input.nextInt(); }}


86

Initializing arrays with random values

for (int row = 0; row < matrix.length; row++) { for (int column = 0; column < matrix[row].length; column++) { matrix[row][column] = (int)(Math.random() * 100); }}


87

Printing arrays

for (int row = 0; row < matrix.length; row++) { for (int column = 0; column < matrix[row].length; column++) { System.out.print(matrix[row][column] + " "); }

System.out.println();}


88

Summing all elements

int total = 0;for (int row = 0; row < matrix.length; row++) { for (int column = 0; column < matrix[row].length; column++) { total += matrix[row][column]; }}


89

Summing elements by column

for (int column = 0; column < matrix[0].length; column++) { int total = 0; for (int row = 0; row < matrix.length; row++) total += matrix[row][column]; System.out.println("Sum for column " + column + " is " + total);}

90

// Package Declarationimport java.lang.*; // not required

// Program start class public class HelloWorld { // Main begins program execution public static void main(string[] args) { // This is a single line comment

/* This is a multiple line comment */

System.out.println("Hello World!"); } }

Demo programs - Example

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import java.util.*;

public class test11 {

public static void main(String[] args) {

System.out.println("Hello, it’s: ");

System.out.println(new Date());

}

}

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Demo Programs

Demonstrate end-of-file controlled loop using standard input from the keyboard and standard output to the screen

Solution to implement in a version:as console application

Problem:To accumulate sum of stream of input integers

terminated by end-of-data (CTRL/Z) indicator

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Demo Program – Source Code

// Java demo program, standard Input (keyboard) / Output (screen)// Class Scanner (Import java.util.Scanner;)// Methods next(), nextInt(), nextFloat(), nextDouble(), nextLine(), hasNext()

import java.util.Scanner;public class Main { public static void main(String[] args) { int sum=0, arg; Scanner cin = new Scanner(System.in); while (cin.hasNext()) { sum += cin.nextInt(); } System.out.println("Final sum = " + sum); }}

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Thank You For

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Lesson 2 The Java Prog Lan AUBG ICoSCIS Team Assoc. Prof. Stoyan Bonev March, 23 - 24, 2013 SWU,...

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Transcript of Lesson 2 The Java Prog Lan AUBG ICoSCIS Team Assoc. Prof. Stoyan Bonev March, 23 - 24, 2013 SWU,...