LECTURE 1 JAVA FUNDAMENTALS

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CSC- 210

Object Oriented Programming

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LECTURE 1

JAVA FUNDAMENTALS

OUTLINE

• Basic elements of Java

• I/O statements in Java

• Selection statements in Java

• Repetition statements in Java

• Arrays in Java

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Header files

Include a sequence of header files.

return 0; }

Global Variables & Function Declaration

Give a descriptive name to the main class.

int main (void){

Method Body

Include a sequence of instructions.

Return Type

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Program Template for simple JAVA Program

Import Statements

Include a sequence of import statements.

public class

_{

} }

Class Name

Give a descriptive name to the main class.

public static void main (String[] args){

Method Body

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• Package is a container for classes .

• A package is a grouping of related types (classes and interfaces) providing access protection and name space management.

• In simple words, packages is the way we organize files into different directories according to their functionality, usability as well as category they should belong to.

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WHY DO WE NEED PACKAGES?

• One can easily determine that these types are related.

• One knows where to find types that can provide task-related functions.

• The names of your types won't conflict with the type names in other packages because the package creates a new namespace.

• One can allow types within the package to have unrestricted access

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ORGANIZING CLASSES WITH

PACKAGE

package bahria.academics; class Student { }

The “package” keyword provides namespace for the classes (=systematic grouping of related classes)

a. For example, the package bahria.transport can be used to store classes such as Car, Transit, Bus, Driver, etc.

b. On the other hand, the package bahria.academics can be used to store classes such as Student, Lecturer, Course, Program, etc..

If omitted, the class is automatically stored in the default package. The package statement should be declared in the first non-comment line.

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PACKAGES IN JAVA

• A package is a namespace that organizes a set of related types, such as classes and interfaces.

• The syntax to create a package is:

package <package name>;

• An example to create package:

package test;

class PackageDemo{}

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PACKAGES IN JAVA

• A class can access the classes in another package by importing the required package.

• The syntax to import a package is:

import <package name>.*;

• An example to import a package:

import test.*; class Demo{

}

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CLASSES

•

Classes built for real world objects that cannot be

represented using available types

•

A class is an "extension" of Java

•

Definition of class:

“A group or category of things that have a set of attributes in

common.“

•

In programming: a pattern, blueprint, or template for

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CLASS DECLARATION

Syntax:

class className

{

// Attributes (variables & constants) // and behaviors (methods)

}

Where

• className is the name of a reference type

•

And { } mark the boundaries of the declaration

Example

package Lecture2;

public class Welcome {

public static void main(String[] args) {

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

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Hello World in C++ and JAVA

public class HelloWorld {

public static void main(String [] args) {

System.out.println(“Hello World!”); } //main end

} //class end

#include <iostream>

using namespace std;

int main() {

cout << "Hello World!" << endl; return 0;

} //main end

Hello.cpp HelloWorld.java

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Keyboard Input in C++ and JAVA

import java.util.Scanner;

public class Input {

public static void main(String [] args) { int a,b;

Scanner input = new Scanner(System.in); System.out.println(“Enter the values of a and b”); a = input.nextInt();

b = input.nextInt();

System.out.println(“a =“+a+”b=“+b); } //main end

}//class end #include <iostream>

using namespace std;

int main() { int a,b;

cout << “Enter the values of a and b" << endl; cin>>a>>b;

cout<<“a =“<<a<<“b=“<<b; return 0;

}

//main end

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Sample Program (Scanner Class)

class MyClass {

public static void main(String[] args){

Scanner input= new Scanner(System.in);

int num1;

System.out.println(“Enter 1st Value: ");

num1=input.nextInt();

System.out.println(“Number Entered = " + num1);

}

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This the Package which contain the classes for getting input from the user

class MyClass {

int num1;

}

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Import is used to include external packages in your code

class MyClass {

int num1;

}

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Here we are creating an object of the Scanner class that we have imported in out java code… where input is name of the object… by the help of this input object we are going to take input from the users.

class MyClass {

int num1;

}

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class MyClass {

int num1;

}

new reserved word is used to create an object of the

class…

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System.in is an input stream

class MyClass {

int num1;

}

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input.nextInt() would take the input from the user and would assign it to a variable num1.

class MyClass {

int num1;

}

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SCANNER CLASS METHODS

Method-Name _Function

nextBoolean() reads one boolean value (true/false) nextByte() reads one byte value

nextShort() reads one short value nextInt() reads one int value nextLong() reads one long value nextFloat() reads one float value nextDouble() reads one double value

next() reads one string of non-whitespace characters

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IDENTIFIER, VARIABLE, CONSTANT

• Identifier is a name that we associate with some program entity (class name, variable name, parameter name, etc.)

• Java Identifier Rule:

• May consist of letters (‘a’ – ‘z’, ‘A’ – ‘Z’), digit characters (‘0’ – ‘9’), underscore (_) and dollar sign ($)

• Cannot begin with a digit character

• Variable is used to store data in a program

• A variable must be declared with a specific data type • Eg:

• Constant is used to represent a fixed value

• Eg:

• Keyword final indicates that the value cannot change

int countDays, $total, _total, total5; double priceOfItem;

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Class name: UpperCamelCase

Eg: Math, HelloWorld, ConvexGeometricShape

Variable name: LowerCamelCase

Eg: countDays, innerDiameter, numOfCoins

Constant: All uppercase with underscore

Eg: PI, CONVERSION_RATE, CM_PER_INCH

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COMMENTS

Java supports three types of comments:

………..

………*/

Delimeter Use

// Used for commenting a single line

/* ————— */ Used for commenting a block of code

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Type Name Size (#bytes) Range Default Value

byte 1 –128 to 127 0

short 2 –32,768 to 32,767 0

int 4 –2,147,483,648 to 2,147,483,647 0

long 8 -9,223,372,036,854,775,808 to

9,223,372,036,854,775,807

0L

float 4 Negative: -3.4028235E+38 to -1.4E-45

Positive: 1.4E-45 to 3.4028235E+38

0.0f

double 8 Negative: -1.7976931348623157E+308 to

-4.9E-324

Positive: 4.9E-324 to 1.7976931348623157E+308

0.0d

char 2 '\u0000‘ to '\uffff' '\u0000' String - 2,147,483,647 characters null

boolean 1 bit true/false false

Integer Data

Types

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NUMERIC DATA TYPE

CONVERSION

• When operands of an operation have differing types:

• If one of the operands is double, convert the other to double

• Otherwise, if one of them is float, convert the other to float

• Otherwise, if one of them is long, convert the other to long

• Otherwise, convert both into int

• When value is assigned to a variable of differing types:

• Widening (Promotion):

• Value has a smaller range compared to the variable • Converted automatically

• Narrowing (Demotion):

• Value has a larger range compared to the variable

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Conversion mistake

double d; int i;

i = 31415; d = i / 10000;

What’s the mistake? How do you correct it?

Type casting

double d; int i;

d = 3.14159;

i = (int)d; // i is assigned 3

The (int)d expression is known as type casting Syntax:

(datatype) value Effect:

value is converted explicitly to the data type stated if possible.

Q: What is assigned to i if d contains 3.987 instead?

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Operator Type Category Precedence

Unary postfix expr++

expr--prefix ++expr --expr +expr -expr ~ !

Arithmetic multiplicative * / %

additive +

-Shift shift << >> >>>

(System.out.println(Integer.toBinaryString(2 << 11));)

Relational comparison < > <= >= instanceof

equality == !=

Bitwise bitwise AND &

bitwise exclusive OR ^

bitwise inclusive OR |

Logical logical AND &&

logical OR ||

Ternary ternary ? : (result = testCondition ? value1 : value2)

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PROBLEM: FAHRENHEIT TO

CELSIUS

•

Write a simple Java program Temperature.Java:

• To convert a temperature reading in Fahrenheit, a real number, to

Celsius degree using the following formula:

• Print out the result

•

For the time being, you can hard code a value for the

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• public class Temperature {

• public static void main(String[] args) {

• double fahrenheit, celsius;

• fahrenheit = 123.5;

• celsius = (5.0/9) * (fahrenheit – 32);

• System.out.println("Celsius: " + celsius);

• }

SOLUTION: FAHRENHEIT TO

CELSIUS

• Notes:

• 5.0/9 is necessary to get the correct result (what will 5/9 give?)

• “+” in the printing statement

• Concatenate operator, to combine strings into a single string • Variable values will be converted to string automatically

• There is another printing statement, System.out.print(), which does not include newline at the end of line

Temperature.java

• Compare with C:

• printf("Celsius: %f\n", celsius);

• Output:

• Celsius:

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Writing Output: The Standard Output

•

System.out is the predefined output device

• Refers to the monitor/screen of your computer

SYNTAX

//Functionality provided

System.out.print( output_string );

System.out.println( output_string );

System.out.printf( format_string, [items] );

System.out.print("ABC"); System.out.println("DEF"); System.out.println("GHI");

System.out.printf("Very C-like %.3f\n", 3.14159);

Output:

ABCDEF GHI

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WRITING OUTPUT: printf()

System.out.printf(“%7.5 f”, Math.PI)

format

string number to _print

field width _precision

conversion code

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Type Code Typical literal Sample format strings

Converted string values for output

int d 512 “%14d” “ 512”

“%-14d” “512 “

double f 1595.168001075 4388

“%14.2f” “ 1595.17”

e “%.7f” “1595.1680011”

“%14.4e” “ 1.5952e+03”

String s “Hello, World” “%14s” “ Hello, World”

“%-14s” “Hello, World “

%-14.5s” “Hello “

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CLASS ACTIVITY

PROBLEM: Approximating PI

One way to calculate the PI (π) constant:

Write ApproximatePI.java to:

1. Ask the user for the number of terms to use for

approximation

2. Calculate π with the given number of terms

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import java.util.*; // using * in import statement

public class ApproximatePI {

public static void main(String[] args) {

int nTerms, sign = 1, denom = 1; double pi = 0.0;

Scanner sc = new Scanner(System.in);

System.out.print("Enter number of terms: "); nTerms = sc.nextInt();

for (int i = 0; i < nTerms; i++) { pi += 4.0 / denom * sign; sign *= -1;

denom += 2; }

System.out.printf("PI = %.6f\n", pi); }

} _{ApproximatePI.java}

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ESCAPE SEQUENCES

Escape

Meaning

\n

New line

\t

Tab

\b

Backspace

\r

Carriage return

\\

Backslash

\'

Single quotation mark

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NOTE:

The "expression" in the parentheses for an if statement

or loop

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To conditionally execute more than one statement, you must create a

compound statement (block) by enclosing the statements in braces ( this is true for loops as well ):

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The "expression" and “int-constant” are usually type int or char or String such as “good”:

Use the break keyword to exit the structure (avoid “falling through” other cases).

Use the default keyword to provide a default case if none of the case expressions match .

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int [] scores = {85, 92, 76, 66, 94}; //collection is the array scores for ( int number : scores ) //parameter is the variable number System.out.println(number);

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Write a java program to roll a die for 1000 times and calculate how many times each face appeared?

public class Die0 {

public static final int N = 1000;

Random rand = new Random();

int d1 = 0, d2 = 0, d3 = 0, d4 = 0, d5 = 0, d6 = 0; for (int k = 0; k < N; k++) {

int roll = rand.nextInt(6)+1; if (roll == 1) d1++;

else if (roll == 2) d2++; else if (roll == 3) d3++; else if (roll == 4) d4++; else if (roll == 5) d5++;

else if (roll == 6) d6++; }

System.out.println("Rolls: " + N + “\n 1: " + d1 + “\n 2: " + d2 + “\n 3: " + d3 + “\n 4: " + d4 + “\n 5: " + d5 +

“\n 6: " + d6); } }

ROLLING A DIE (Using if-else)

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Write a java program to roll a die for 1000 times and calculate how many times each face appeared?

Random rand = new Random();

int d1 = 0, d2 = 0, d3 = 0, d4 = 0, d5 = 0, d6 = 0; for (int k = 0; k < N; k++) {

int roll = rand.nextInt(6)+1; switch(roll){

case 1: d1++; break; case 2: d2++; break; case 3: d3++; break; case 4: d4++; break; case 5: d5++; break; case 6: d6++; break; }

System.out.println("Rolls: " + N + “\n 1: " + d1 + “\n 2: " + d2 + “\n 3: " + d3 + “\n 4: " + d4 + “\n 5: " + d5 + “\n 6: " + d6);

}} OUTPUT: Rolls: 1000 1: 172 2: 153 3: 168 4: 175 5: 174 6: 158

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THE MATH CLASS

•

Package: java.lang (default)

•

Some useful

Math

methods:

• Math.pow() – To the power of • Math.sqrt() – The square root

• Math.abs() – Outputs only positive numbers

• Math.random() – Returns a double value with a positive sign, greater

than or equal to 0.0 and less than 1.0.

• Math.round() – Rounds up numbers

• Math.ceil() – Outputs the smallest number • Math.floor() – Outputs the largest number

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HOW TO USE THE MATH CLASS

• You must include the class name Math each time you wish to use the

Math Class

• Example;

System.out.println(Math.pow(2,8));

Indicating you wish to output something

Calling the Math Class

Calling the function power

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The

Math

class: Demo

// To find the area of the largest circle inscribed // inside a square, given the area of the square.

import java.util.*;

public class TestMath {

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

System.out.print("Enter area of a square: ");

double areaSquare = sc.nextDouble();

double radius = Math.sqrt(areaSquare)/2;

double areaCircle = Math.PI * Math.pow(radius, 2); System.out.printf("Area of circle = %.4f\n",

areaCircle); }

}

TestMath.java

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FUNCTIONS / METHODS

• A program that provides some functionality can be long and

contains many statements

• A method groups a sequence of statements and should

provide a well-defined, easy-to-understand functionality

• a method takes input, performs actions, and produces output

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•

A class contains data declarations (static and instance

variables) and method declarations (behaviors)

int month; int year class Month

Data declarations

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METHOD DECLARATION: HEADER

A method declaration begins with a

method header

method name

return type

parameter list

The parameter list specifies the type and name of each parameter

The name of a parameter in the method declaration is called a formal argument

class MyClass

{

static int min ( int num1, int num2 ) …

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METHOD DECLARATION: BODY

The header is followed by the

method body:

static int min(int num1, int num2) {

int minValue = num1 < num2 ? num1 : num2; return minValue;

}

class MyClass {

…

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The

return

Statement

•

The

return type

of a method indicates the type of value that the

method sends back to the calling location

•

A method that does not return a value has a

void

return type

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CALLING A METHOD

•

Each time a method is called, the values of the

actual

arguments

in the invocation are assigned to the

formal

arguments

static int min (int num1, int num2)

{

int minValue = (num1 < num2 ? num1 : num2); return minValue;

}

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•

In Java, C++-like function is known as

static/class method

• Denoted by the “static” keyword before return data type

• Another type of method, known as _{instance method}will be covered later

Factorial.java public class Factorial {

// Returns n!

// Pre-cond: n >= 0

public static int factorial (int n) { if (n == 0) return 1;

else return n * factorial(n-1); }

int n = 5; // You can change it to interactive input

System.out.printf("Factorial(%d) = %d\n", n, factorial(n));

} }

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TWO TYPES OF

PARAMETER PASSING

If a modification of the

formal argument

has

no

effect

on the

actual argument

,

– it is

call by value

If a modification of the

formal argument

can change

the value of the

actual argument

,

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Call-By-Reference in Java

• Depend on the type of the formal argument

• If a formal argument is a primitive data type, a modification on the

formal argument has no effect on the actual argument

• this is call by value, e.g. num1 = min(2, 3);

• num2 = min(x, y);

• This is because primitive data types variables contain their values, and

procedure call trigger an assignment:

• <formal argument> = <actual argument>

int x = 2; int y = 3; int num = min (x, y); …

static int num( int num1, int num2) { … }

int x = 2; int y = 3;

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Call-By-Reference in Java

• If a formal argument is not a primitive data type, an operation on the

formal argument can change the actual argument

• this is call by reference

• This is because variables of object type contain pointers to the data that

represents the object

• Since procedure call triggers an assignment

• <formal argument> = <actual argument>

• it is the pointer that is copied, not the object itself!

MyClass x = new MyClass(); MyClass y = new MyClass(); MyClass.swap( x, y);

…

static void swap( MyClass x1, MyClass x2)

{ … }

x = new MC(); y = new MC(); x1 = x;

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There can be various types of methods (behavior declarations)

• access methods : read or display states (or those that can be derived)

• predicate methods : test the truth of some conditions

• action methods, e.g., print

• constructors: a special type of methods

• they have the same name as the class

• there may be more then one constructor per class (overloaded constructors)

• they do not return any value

• it has no return type, not even void

• they initialize objects of the class, using the new construct:

• e.g. m1 = new Month();

• you do not have to define a constructor

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A list of items can be given one variable name using only one

subscript and such a variable is called a single-subscripted variable or a one-dimensional array.

Creating an Array

Like any other variables, arrays must be declared and created in

the computer memory before they are used.

Array creation involves three steps:

1. Declare an array Variable

2. Create Memory Locations

3. Put values into the memory locations.

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1. DECLARE AN ARRAY

VARIABLE

Arrays in java can be declared in two ways:

i. type arrayname [ ];

ii. type[ ]arrayname;

Example:

int number[]; float slaray[]; float[] marks;

when creating an array, each element of the array receives a default value

zero (for numeric types) ,false for boolean and null for references (any

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2. CREATION OF ARRAYS

After declaring an array, we need to create it in the memory. Because an array is an object, you create it by using the new keyword as follows:

arrayname =new type[ size]; Example:

number = new int[5]; marks = new float[7];

It is also possible to combine the above to steps , declaration and creation,

into on statement as follows:

type arrayname =new type[ size];

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3. INITIALIZATION OF ARRAYS (1/3)

Each element of an array needs to be assigned a value; this process is known as initialization.

Initialization of an array is done using the array subscripts as follows:

arrayname [subscript] = Value; Example:

number[0] = 23; number[2] = 40;

Unlike C, java protects arrays from overruns and underruns.

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3. INITIALIZATION OF ARRAYS (2/3)

• Java generates an ArrayIndexOutOfBoundsException when there is

underrun or overrun.

• The Java interpreter checks array indices to ensure that they are valid

during execution.

• Arrays can also be initialized automatically in the same way as the

ordinary variables when they are declared, as shown below:

type arrayname [] = {list of Values};

Example:

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3. INITIALIZATION OF ARRAYS (3/3)

It is also possible to assign an array object to another array object.

Example:

int array1[]= {35,40,23,67,49};

int array2[];

array2= array1;

array2 is referencing the array1. Any change in Array2 will effect the array1. For Example Array2[0]=44;

System.out.println(“array1[0] =”+ array1[0]); // out will be array1 = 44

Array Length

• In Java, all arrays store the allocated size in a variable named length.

• We can access the length of the array array1using array1.length. Example:

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■

Write a java program to roll a die for 1000 times and calculate how

many times each face appeared?

public static void main(String[] args) { Random rand = new Random();

int[] d = new int[7];

for (int k = 1; k < N; k++) int roll = rand.nextInt(6)+1; d[roll]++;

}

System.out.println("Rolls: " + N); for (int i = 1; i < 7; i++)

System.out.println(i + ": " + d[i]); System.out.println();

} }

ROLLING A DIE (ARRAYS)

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TWO DIMENSIONAL ARRAYS

• A 2-dimensional array can be thought of as a grid (or matrix) of values.

• Each element of the 2-D array is accessed by providing two indexes: a

row index and a column index

• A 2-D array is actually just an array of arrays.

• A multidimensional array with the same number of columns in every row

can be created with an array creation expression:

Example:

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TWO DIMENSIONAL ARRAYS

• Like the one-dimensional arrays, two-dimensional arrays may be

initialized by following their declaration with a list of initial values

enclosed in braces. For example,

int myarray[2][3]= {0,0,0,1,1,1};

or

int myarray[][]= {{0,0,0},{1,1,1}};

• We can refer to a value stored in a two-dimensional array by using

indexes for both the column and row of the corresponding element. For

Example,

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class MulTable{

final static int ROWS=12; final static int COLUMNS=12;

public static void main(String [ ]args) {

int pro [ ] [ ]= new int [ROWS][COLUMNS];

int i,j;

System.out.print("MULTIPLICATION TABLE");

System.out.println(" "); for (i=1; i<ROWS; i++){

for (j=1; j<COLUMNS; j++){ pro [i][j]= i * j;

System.out.printf(“%4d"+ pro[i][j]);

}

System.out.println(" " ); }

} }

MULTIPLICATION TABLE

1 2 3 4 5 6 7 8 9 10 11 2 4 6 8 10 12 14 16 18 20 22 3 6 9 12 15 18 21 24 27 30 33 4 8 12 16 20 24 28 32 36 40 44 5 10 15 20 25 30 35 40 45 50 55 6 12 18 24 30 36 42 48 54 60 66 7 14 21 28 35 42 49 56 63 70 77 8 16 24 32 40 48 56 64 72 80 88 9 18 27 36 45 54 63 72 81 90 99 10 20 30 40 50 60 70 80 90 100 110 11 22 33 44 55 66 77 88 99 110 121

MulTable.java

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VARIABLE SIZE ARRAYS

• Java treats multidimensional array as “array of arrays”.

• It is possible to declare a two-dimensional array as follows:

• int x[][]= new int[3][];

• x[0] = new int[2];

• x[1] = new int[4];

• x[2] = new int[3];

• This statement creates a two-dimensional array having different length

for each row as shown below:

X[0]

X[1]

X[2]

x[0][1]

x[2][2]

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ARRAYS LENGTH

•

All arrays have a public field named

length

which holds

the number of elements in the array.

•

Given this declaration: int x[][][]= new int[7][5][2] ;

•

x.length

is the number of elements in the array in the first

dimension.

•

x[m].length

is the number of elements for a specific array in

the second dimension.

•

x[m][n].length

is the number of elements for a specific array

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ArrayList (1/3)

• The array is a data structure that is fixed in size,

once created, the size can not be changed anymore.

• ArrayList created to address the problems faced by

Array in determining its size because it is a dynamic

ArrayList

• Declaration:

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ArrayList Methods (2/3)

The following functions are often used in class Array List:

– add (element) add elements to the list

– clear () removes all elements in the list

– clone () returns the copied object in the list

– containts(element) search for elements that exist in

the list

– get (index) take element in a particular index in the list

– isEmpty () check whether the list is empty or not

– remove (index) removes the element designated in

the list

– size () number of elements in the list

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Vector (1/3)

1. Vector is another collection class in the package java.util.

2. Vector is similar to ArrayList, except that it is

synchronized.

3. Synchronized means that Vector is thread-safe. We will

leave out the discussion of thread-safe from this module.

4. However, Vector is slower than ArrayList.

5. Declaration

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Vector Methods(2/3)

The following functions are often used in the Vector class:

• addElement (element) add elements to the final sequence of the vector • capacity () Returns capacity vector

• clone () returns the copied object in the vector

• containts (element) search for existing element in the vector • copyInto (element []) copy specific elements to the array • ElementAt (index) take the elements of the designated index

• insertElementAt (element, index) add an element to the designated index.

• isEmpty () check whether the vector is empty or not

• remove (index) removes the element designated in the vector • size () number of elements in the vector

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