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7/31/2019 JavaProgramming_SlideNotes1

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CAREER ENTRY COURSE FOR SOFTWARE DEVELOPERS - JAVA

JAVA

PROGRAMMINGLANGUAGE


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Simple Input/OutputOperation

Objectives Simple Input Command

Character

String

Simple Output Command

Convert String to

Integer Real

Programming Exercises


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Simple Input Command

The form of input can be keyboardentry from the user.

Values input by user can be numerical

or non-numerial. Java has some standard input

commands that allows the user to usethe commands to input values via thekeyboard.

We shall look at the character andString input


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Character Input Command

Characters are read from the keyboardusing System.in.read() method.

One of Javas console function.

Accepts input from the keyboard.

in object has access to method read()which retrieves data from keyboard.

The main() method header had aphrase throws Exception added at theend of the line.


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Character Input Command

Exception is an error situation, bythrowing the exception, thecompiler will handle the differentsorts of errors.

Programs accepting input fromkeyboard will not be able to

compile successfully without thephrase throws Exception.


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String Input Command

TheInputStreamReader() is used toread characters from the keyboard.

The BufferedReader() is used, for it

provides the readLine() methodtoallow programs to read from keyboarda line at a time.

Java implements I/O operationsthrough streams.

Represented by two abstract classes,InputStream and OutputStream.


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String Input Command

These are found injava.iopackage.

Thus, have to import this packageinto the program, which is placeat the beginning of the program.


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Simple Output Command

System.outis a PrintStream object thatallows output to be displayed.

Two methods used, i.e.print() and

println() method. print() method allows the cursor to be

positioned on the next availableposition on the same line.

println() method allows the cursor tobe positioned on the next line.


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Convert String to Integer

Converts String containingnumbers to numerical data toperform arithmetic calculation.

Use teIntegerclass, which is partof thejava.lang package.

parseInt() method from the

Integerclass is used to convertString to integer.


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Convert String to Real

Use the Double class, which ispart of thejava.lang package.

parseDouble() method from theDouble class is used to convertString to real numbers.


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Q1) Write a Java program to capture theusers name and age and displays thename and converts the age to aninteger and displays the age with ameaningful message.


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Control Structures

Objectives To write Selection statements

To write Iteration statements



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Selection Statements

Based on the user input, decision making willtake place.

It involves choosing between two alternativecourses of action.

Java supports two kinds of selection statements

The if, if..else or nested ifstatement

Theswitch statement


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The ifstructure

A single-alternate ifas it only performs anaction based on one alternative.

The if..else structure A dual-alternate ifas it requires two

options for the next course of action.

Performs one action when a booleanexpression evaluates as true and another

when the boolean expression evaluates asfalse.


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The Nested ifstructure

An ifwithin another ifstatement.

Nested ifstatements are useful

when two conditions must be metbefore some action is taken.

Theswitch structure

Another alternative for nested if

statements. Useful when testing single variable

against a series of exact integer orcharacter values.


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Example ofif statement#1

class SampleIf{

public static void main(String[] test) {

int number = 5;

if(number > 0){

System.out.println(The number is positive.);

}

else

System.out.println(The number is negative.);

}}


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Example ofif statement#2

class SampleIf {

public static void main(String args[]) {

System.out.print("Hello ");

System.out.println(args.length);

if (args.length > 0) {

System.out.println(args[0]); }

if (args.length


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Example ofswitchstatement

class SampleIf {

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

char ans , upans ;

System.out.println("Enter A or B ");ans = (char) System.in.read();

upans = Character.toUpperCase(ans);

switch (upans) {

case 'A :System.out.println(" First option");

break;

case 'B :System.out.println(" Second option");

break; }

} }


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Iteration Statements

A structure that allows a block of statementsto be executed repeatedly depending on theevaluation of the boolean expression.

A loop that never ends is called an endless loop

or infinite loop.

A loop within a loop is called a nested loop.

Java supports three kinds of iterationstatements

The while loop The do..while loop

The forloop


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The while loop

Used to repeat a statement or block only ifthe condition is true.

The do..while loop

Used when we need to execute the loopbody at least once before checking thecondition.

like the while loop, it will only repeat astatement or block if the condition is true.


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The testing of the condition is placed differently

while loop test the condition first, thenexecute the body of statements.

do.. while execute the body of statementsbefore testing the condition.


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Example ofwhile loop #1class SampleWhile{public static void main(String[] test) {

int count = 1;

System.out.println(Good Day!);while (count


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Example ofwhile loop #2

class SampleWhile{


int num = 1;

while (num < 5) {System.out.print(num*2);

num = num + 1;

}

}

}


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Example ofdo-while loop #1

class SampleDoWhile{public static void main(String[] test) {

int count = 1;

System.out.println(Good Day!);do {System.out.print(INFORMATICS);count = count + 1;

} while (count


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Example ofdo-while loop #2

class SampleDoWhile{


int num = 1;

do {System.out.print(num*2);

num = num + 1;

} while (num < 5) ;

}

}


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The forloop

Allows the statements in the loop body tobe executed a specific number of times.


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Example offor loop #1

class SampleFor{


System.out.println(Good Day!);

for(int count = 1; count


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Example offor loop #2class SampleFor {public static void main(String[] test) {

System.out.println(ASCII");

for (int count = 0 ; count


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Example offor loop #3class SampleFor {


System.out.println("Graphics ");

for (int x = 1; x


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Write a Java program to capture the users nameand age

and display a message based on the followinginformation:

if age > 65 display retired

if age is between 22 to 65 display working

if age is between 7 to 21 display studying

if age < 7 display playing

The user will be prompted to enter another nameand age.

If the user decides not to enter another name, the

program will terminate.