WAP-Introduction To Java

1. Print an integer input from user to screen

2. Add two integers (assume inputs)

3. Multiplication of two floating numbers (assume inputs)

4. ASCII equivalent of a character

5. Division of integers (quotient & remainder) with no decimal places

6. Swapping of two numbers

7. Odd or Even Integer

8. Alphabets are vowels or consonants

9. Largest among three integers

10. All roots of a quadratic equation

11. Frequency of character

12. Remove whitespaces from a string

13. Round a Number to n Decimal Places

14. String is Empty or Null

Print an integer input from user to screen

In this program, we'll learn to print a number entered by the user . The integer is stored in a

variable using System.in, and is displayed on the screen using System.out.

import java.util.Scanner;

public class HelloWorld {

public static void main(String[] args) {

// Creates a reader instance which takes

// input from standard input - keyboard

Scanner reader = new Scanner(System.in);

System.out.print("Enter a number: ");

// nextInt() reads the next integer from the keyboard

int number = reader.nextInt();

// println() prints the following line to the output screen

System.out.println("You entered: " + number);

}

Output

Enter a number: 10

You entered: 10

In this program, an object of Scanner class, reader, is created to take inputs from standard

input, which is keyboard.

Then, Enter a number prompt is printed to give the user a visual cue as to what they should do

next.

reader.nextInt() then reads all entered integers from the keyboard unless it encounters a new

line character \n (Enter). The entered integers are then saved to the integer variable number.

If you enter any character which is not an integer, the compiler will throw an

InputMismatchException.

Finally, number is printed onto the standard output (System.out) - computer screen using the

function println().

Add two integers (assume inputs)

In this program, we'll learn to store and add two integer numbers . After addition, the final sum is

displayed on the screen.

class Main {

public static void main(String[] args) {

System.out.println("Enter two numbers");

int first = 10;

int second = 20;

System.out.println(first + " " + second);

// add two numbers

int sum = first + second;

System.out.println("The sum is: " + sum);

}

Output:

Enter two numbers

10 20

The sum is: 30

In this program, two integers 10 and 20 are stored in integer variables first and second

respectively.

Then, first and second are added using the + operator, and its result is stored in another

variable sum.

Finally, sum is printed on the screen using println() function.

Multiplication of two floating numbers (assume inputs)

In this program, we'll learn to multiply two floating point numbers , store the result and display it

on the screen.

public class MultiplyTwoNumbers {

public static void main(String[] args) {

float first = 1.5f;

float second = 2.0f;

float product = first * second;

System.out.println("The product is: " + product);

}

Output

The product is: 3.0

In the above program, we have two floating-point numbers 1.5f and 2.0f stored in variables first

and second respectively.

Notice, we have used f after the numbers. This ensures the numbers are float, otherwise they

will be assigned - type double.

first and second are then multiplied using the * operator and the result is stored in a new float

variable product.

Finally, the result product is printed on the screen using println() function.

ASCII equivalent of a character

In this program, we'll learn to find and display the ASCII value of a character . This is done using

type-casting and normal variable assignment operations.

public class AsciiValue {

public static void main(String[] args) {

char ch = 'a';

int ascii = ch;

// You can also cast char to int

int castAscii = (int) ch;

System.out.println("The ASCII value of " + ch + " is: " + ascii);

System.out.println("The ASCII value of " + ch + " is: " +

castAscii);

}

Output

The ASCII value of a is: 97

In the above program, character a is stored in a char variable, ch. Like, double quotes (" ") are

used to declare strings, we use single quotes (' ') to declare characters.

Now, to find the ASCII value of ch, we just assign ch to an int variable ascii. Internally, Java

converts the character value to an ASCII value.

We can also cast the character ch to an integer using (int). In simple terms, casting is

converting a variable from one type to another, here char variable ch is converted to an int

variable castAscii.

Finally, we print the ascii value using the println() function.

Division of integers (quotient & remainder) with no decimal places

In this program, we'll learn to compute quotient and remainder from the given dividend and

divisor in Java.

public class QuotientRemainder {

public static void main(String[] args) {

int dividend = 25, divisor = 4;

int quotient = dividend / divisor;

int remainder = dividend % divisor;

System.out.println("Quotient = " + quotient);

System.out.println("Remainder = " + remainder);

}

Output:

Quotient = 6

Remainder = 1

In the above program, we have created two variables dividend and divisor. Here, we are

calculating the quotient and remainder by dividing 25 by 4.

To find the quotient, we have used the / operator. We have divided dividend (25) by divisor (4).

Since both dividend and divisor are integers, the result will also be integer.

25 / 4 // results 6.5

// convert 6.5 to integer

// output will be 6

Likewise, to find the remainder we use the % operator. Here, the dividend is divided by the

divisor and the remainder is returned by the % operator.

25 % 4 // results 1

Finally, quotient and remainder are printed on the screen using println() function.

Swapping of two numbers

In this program, we'll learn two techniques to swap two numbers in Java. The first one uses a

temporary variable for swapping, while the second one doesn't use any temporary variables.

Using temporary variable

public class SwapNumbers {

public static void main(String[] args) {

float first = 1.20f, second = 2.45f;

System.out.println("--Before swap--");

System.out.println("First number = " + first);

System.out.println("Second number = " + second);

// Value of first is assigned to temporary

float temporary = first;

// Value of second is assigned to first

first = second;

// Value of temporary (which contains the initial value of first)

is assigned to second

second = temporary;

System.out.println("--After swap--");

System.out.println("First number = " + first);

System.out.println("Second number = " + second);

}

Output:

--Before swap--

First number = 1.2

Second number = 2.45

--After swap--

First number = 2.45

Second number = 1.2

In the above program, two numbers 1.20f and 2.45f which are to be swapped are stored in

variables: first and second respectively.

The variables are printed before swapping using println() to see the results clearly after

swapping is done.

1. First, the value of first is stored in variable temporary (temporary = 1.20f).

2. Then, value of second is stored in first (first = 2.45f).

3. And, finally value of temporary is stored in second (second = 1.20f).

This completes the swapping process and the variables are printed on the screen.

Remember, the only use of temporary is to hold the value of first before swapping. You can also

swap the numbers without using temporary.

without using temporary variable

public class SwapNumbers {

public static void main(String[] args) {

float first = 12.0f, second = 24.5f;

System.out.println("--Before swap--");

System.out.println("First number = " + first);

System.out.println("Second number = " + second);

first = first - second;

second = first + second;

first = second - first;

System.out.println("--After swap--");

System.out.println("First number = " + first);

System.out.println("Second number = " + second);

}

Output:

--Before swap--

First number = 12.0

Second number = 24.5

--After swap--

First number = 24.5

Second number = 12.0

In the above program, instead of using temporary variable, we use simple mathematics to swap

the numbers.

For the operation, storing (first - second) is important. This is stored in variable first.

first = first - second;

first = 12.0f - 24.5f

Then, we just add second (24.5f) to this number - calculated first (12.0f - 24.5f) to swap the

number.

second = first + second;

second = (12.0f - 24.5f) + 24.5f = 12.0f

Now, second holds 12.0f (which was initially value of first). So, we subtract calculated first (12.0f

- 24.5f) from swapped second (12.0f) to get the other swapped number.

first = second - first;

first = 12.0f - (12.0f - 24.5f) = 24.5f

The swapped numbers are printed on the screen using println().

Odd or Even Integer

In this program, you'll learn to check if a number entered by a user is even or odd. This will be

done using if...else statement and ternary operator in Java.

Using conditional branching (if-else)

import java.util.Scanner;

public class EvenOdd {

public static void main(String[] args) {

Scanner reader = new Scanner(System.in);

System.out.print("Enter a number: ");

int num = reader.nextInt();

if(num % 2 == 0)

System.out.println(num + " is even");

else

System.out.println(num + " is odd");

}

Output

Enter a number: 12

12 is even

In the above program, a Scanner object, reader is created to read a number from the user's

keyboard. The entered number is then stored in a variable num.

Now, to check whether num is even or odd, we calculate its remainder using % operator and

check if it is divisible by 2 or not.

For this, we use if...else statement in Java. If num is divisible by 2, we print num is even. Else,

we print num is odd.

We can also check if num is even or odd by using ternary operator in Java.

Using ternary operator

import java.util.Scanner;

public class EvenOdd {

public static void main(String[] args) {

Scanner reader = new Scanner(System.in);

System.out.print("Enter a number: ");

int num = reader.nextInt();

String evenOdd = (num % 2 == 0) ? "even" : "odd";

System.out.println(num + " is " + evenOdd);

}

Output

Enter a number: 13

13 is odd

In the above program, we've replaced if...else statement with ternary operator (? :).

Here, if num is divisible by 2, "even" is returned. Else, "odd" is returned. The returned value is

saved in a string variable evenOdd.

Then, the result is printed on the screen using string concatenation.

Alphabets are vowels or consonants

In this program, you'll learn to check whether an alphabet is a vowel or a consonant using

if..else and switch statements in Java.

Using if..else statement

public class VowelConsonant {

public static void main(String[] args) {

char ch = 'i';

if(ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u' )

System.out.println(ch + " is vowel");

else

System.out.println(ch + " is consonant");

}

Output

i is vowel

In the above program, 'i' is stored in a char variable ch. In Java, you use double quotes (" ") for

strings and single quotes (' ') for characters.

Now, to check whether ch is vowel or not, we check if ch is any of: ('a', 'e', 'i', 'o', 'u'). This is

done using a simple if..else statement.

Using switch statement

public class VowelConsonant {

public static void main(String[] args) {

char ch = 'z';

switch (ch) {

case 'a':

case 'e':

case 'i':

case 'o':

case 'u':

System.out.println(ch + " is vowel");

break;

default:

System.out.println(ch + " is consonant");

}

Output

z is consonant

In the above program, instead of using a long if condition, we replace it with a switch case

statement.

If ch is either of cases: ('a', 'e', 'i', 'o', 'u'), vowel is printed. Else, default case is executed and

consonant is printed on the screen.

Largest among three integers

In this program, you'll learn to find the largest among three numbers using if else and nested

if..else statement in Java.

Using if..else statement

public class Largest {

public static void main(String[] args) {

double n1 = -4.5, n2 = 3.9, n3 = 2.5;

if( n1 >= n2 && n1 >= n3)

System.out.println(n1 + " is the largest number.");

else if (n2 >= n1 && n2 >= n3)

System.out.println(n2 + " is the largest number.");

else

System.out.println(n3 + " is the largest number.");

}

}

Output

3.9 is the largest number.

In the above program, three numbers -4.5, 3.9 and 2.5 are stored in variables n1, n2 and n3

respectively.

Then, to find the largest, the following conditions are checked using if else statements

1. If n1 is greater or equals to both n2 and n3, n1 is the greatest.

2. If n2 is greater or equals to both n1 and n3, n2 is the greatest.

3. Else, n3 is the greatest.

Using nested if..else statement

public class Largest {

public static void main(String[] args) {

double n1 = -4.5, n2 = 3.9, n3 = 5.5;

if(n1 >= n2) {

if(n1 >= n3)

System.out.println(n1 + " is the largest number.");

else

System.out.println(n3 + " is the largest number.");

} else {

if(n2 >= n3)

System.out.println(n2 + " is the largest number.");

else

System.out.println(n3 + " is the largest number.");

}

Output

5.5 is the largest number.

In the above program, instead of checking for two conditions in a single if statement, we use

nested if to find the greatest.

Then, to find the largest, the following conditions are checked using if else statements

1. If n1 is greater or equals to n2,

a. and if n1 is greater or equals to n3, n1 is the greatest.

b. else, n3 is the greatest.

2. Else,

a. if n2 is greater or equals to both n3, n2 is the greatest.

b. else, n3 is the greatest.

All roots of a quadratic equation

In this program, you'll learn to find all roots of a quadratic equation and print them using format()

in Java.

The standard form of a quadratic equation is:

ax² + bx + c = 0

Here, a, b, and c are real numbers and a can't be equal to 0.

We can calculate the root of a quadratic by using the formula:

x = (-b ± √(b²-4ac)) / (2a)

The ± sign indicates that there will be two roots:

root1 = (-b + √(b²-4ac)) / (2a)

root1 = (-b - √(b²-4ac)) / (2a)

The term b²-4ac is known as the determinant of a quadratic equation. It specifies the nature of

roots. That is,

● if determinant > 0, roots are real and different

● if determinant == 0, roots are real and equal

● if determinant < 0, roots are complex complex and different

public class Main {

public static void main(String[] args) {

// value a, b, and c

double a = 2.3, b = 4, c = 5.6;

double root1, root2;

// calculate the determinant (b2 - 4ac)

double determinant = b * b - 4 * a * c;

// check if determinant is greater than 0

if (determinant > 0) {

// two real and distinct roots

root1 = (-b + Math.sqrt(determinant)) / (2 * a);

root2 = (-b - Math.sqrt(determinant)) / (2 * a);

System.out.format("root1 = %.2f and root2 = %.2f", root1, root2);

}

// check if determinant is equal to 0

else if (determinant == 0) {

// two real and equal roots

// determinant is equal to 0

// so -b + 0 == -b

root1 = root2 = -b / (2 * a);

System.out.format("root1 = root2 = %.2f;", root1);

}

// if determinant is less than zero

else {

// roots are complex number and distinct

double real = -b / (2 * a);

double imaginary = Math.sqrt(-determinant) / (2 * a);

System.out.format("root1 = %.2f+%.2fi", real, imaginary);

System.out.format("\nroot2 = %.2f-%.2fi", real, imaginary);

}

Output

root1 = -0.87+1.30i and root2 = -0.87-1.30i

In the above program, the coefficients a, b, and c are set to 2.3, 4, and 5.6 respectively. Then,

the determinant is calculated as b² - 4ac.

Based on the value of the determinant, the roots are calculated as given in the formula above.

Notice we've used library function Math.sqrt() to calculate the square root of a number.

We have used the format() method to print the calculated roots.

The format() function can also be replaced by printf() as:

System.out.printf("root1 = root2 = %.2f;", root1);

Frequency of character

In this program, you'll learn to find the occurence (frequency) of a character in a given string.

public class Frequency {

public static void main(String[] args) {

String str = "This website is awesome.";

char ch = 'e';

int frequency = 0;

for(int i = 0; i < str.length(); i++) {

if(ch == str.charAt(i)) {

++frequency;

}

System.out.println("Frequency of " + ch + " = " + frequency);

}

Output

Frequency of e = 4

In the above program, the length of the given string, str, is found using the string method

length().

We loop through each character in the string using charAt() function which takes the index (i)

and returns the character in the given index.

We compare each character to the given character ch. If it's a match, we increase the value of

frequency by 1.

In the end, we get the total occurrence of a character stored in frequency and print it.

Remove whitespaces from a string

In this program, you'll learn to remove all whitespaces in a given string using regular

expressions in Java.

public class Whitespaces {

public static void main(String[] args) {

String sentence = "T

his is b ett

er.";

System.out.println("Original sentence: " + sentence);

sentence = sentence.replaceAll("\\s", "");

System.out.println("After replacement: " + sentence);

}

Output

Original sentence: T

his is b ett

er.

After replacement: Thisisbetter.

In the above program, we use String's replaceAll() method to remove and replace all

whitespaces in the string sentence.

We've used regular expression \\s that finds all white space characters (tabs, spaces, new line

character, etc.) in the string. Then, we replace it with "" (empty string literal).

Take string from user

import java.util.Scanner;

class Main {

public static void main(String[] args) {

// create an object of Scanner

Scanner sc = new Scanner(System.in);

System.out.println("Enter the string");

// take the input

String input = sc.nextLine();

System.out.println("Original String: " + input);

// remove white spaces

input = input.replaceAll("\\s", "");

System.out.println("Final String: " + input);

sc.close();

}

Output

Enter the string

J av a- P rog ram m ing

Original String: J av a- P rog ram m ing

Final String: Java-Programming

Here, the replaceAll() method replaces all the white spaces from the string.

Round a Number to n Decimal Places

In this program, you'll learn to round a given number to n decimal places in Java.

Using format

public class Decimal {

public static void main(String[] args) {

double num = 1.34567;

System.out.format("%.4f", num);

}

Output

1.3457

In the above program, we've used the format() method to print the given floating-point number

num to 4 decimal places. The 4 decimal places are given by the format .4f.

This means, print only up to 4 places after the dot (decimal places), and f means to print the

floating-point number.

Using DecimalFormat

import java.math.RoundingMode;

import java.text.DecimalFormat;

public class Decimal {

public static void main(String[] args) {

double num = 1.34567;

DecimalFormat df = new DecimalFormat("#.###");

df.setRoundingMode(RoundingMode.CEILING);

System.out.println(df.format(num));

}

Output

1.346

In the above program, we've used DecimalFormat class to round a given number num.

We declare the format using the # patterns #.###. This means we want num up to 3 decimal

places. We also set the rounding mode to Ceiling, this causes the last given place to be rounded

to its next number.

So, 1.34567 rounded to 3 decimal places prints 1.346, 6 is the next number for 3rd place

decimal 5.

String is Empty or Null

In this program, you'll learn to check if a string is empty or null using a method and the if-else

statement in Java.

class Main {

public static void main(String[] args) {

// create null, empty, and regular strings

String str1 = null;

String str2 = "";

String str3 = " ";

// check if str1 is null or empty

System.out.println("str1 is " + isNullEmpty(str1));

// check if str2 is null or empty

System.out.println("str2 is " + isNullEmpty(str2));

// check if str3 is null or empty

System.out.println("str3 is " + isNullEmpty(str3));

}

// method check if string is null or empty

public static String isNullEmpty(String str) {

// check if string is null

if (str == null) {

return "NULL";

}

// check if string is empty

else if(str.isEmpty()){

return "EMPTY";

}

else {

return "neither NULL nor EMPTY";

}

Output

str1 is NULL

str2 is EMPTY

str3 is neither NULL nor EMPTY

In the above program, we have created

● a null string str1

● an empty string str2

● a string with white spaces str3

● method isNullEmpty() to check if a string is null or empty

Here, str3 only consists of empty spaces. However, the program doesn't consider it an empty

string.

This is because white spaces are treated as characters in Java and the string with white spaces

is a regular string.

Now, if we want the program to consider strings with white spaces as empty strings, we can use

the trim() method. The method removes all the white spaces present in a string.

String with spaces is Empty or Null

class Main {

public static void main(String[] args) {

// create a string with white spaces

String str = "

// check if str1 is null or empty

System.out.println("str is " + isNullEmpty(str));

}

// method check if string is null or empty

public static String isNullEmpty(String str) {

// check if string is null

if (str == null) {

return "NULL";

}

// check if string is empty

else if (str.trim().isEmpty()){

return "EMPTY";

}

else {

return "neither NULL nor EMPTY";

}

Output

str is EMPTY

In the above example, notice the condition to check empty string

else if (str.trim().isEmpty())

Here, we have used the trim() method before isEmpty(). This will

1. remove all the white spaces present inside the string

2. check if the string is empty

Hence, we get str is EMPTY as output.

[Programs] Introduction To Java

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[Programs] Introduction To Java

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