InstanceOfJava

How to generate unique random numbers in java

Posted by: Instanceofjava Posted date: 11:06 PM / comment : 1 java programming interview questions

In java we can generate random number in two ways
By using Random class
By using Math.random

Program #1: Java Example program to generate random numbers using random class within the range of 1 to 10

First we need to create object of java.util.Random class.
After creating object of java.util.Random class then we need call nextInt() method by passing range
int range = maximum - minimum + 1;
int randomNum = rn.nextInt(range) + minimum;

package com.randomnumbergenerator;
import java.util.Random;
import java.util.Scanner;
public class RandomNumber {
/**
* @Website: www.instanceofjava.com
* @category: how to generate random numbers in java within range
*/
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.println("Enter minimum number");
int minimum=in.nextInt();
System.out.println("Enter maximum number");
int maximum=in.nextInt();
Random rn = new Random();
int range = maximum - minimum + 1;
int randomNum = rn.nextInt(range) + minimum;
System.out.println("Random Number= "+randomNum);
}
}

Output:

Enter minimum number
1
Enter maximum number
10
Random Number= 4

Program #2: Java Example program to generate random numbers using Math.random within the range of 1 to 10

By using Math.random() method also we can generate random number in java
int randomNum = minimum + (int)(Math.random() * maximum);

package com.randomnumbergenerator;
import java.util.Random;
import java.util.Scanner;
public class RandomNumber {
/**
* @Website: www.instanceofjava.com
* @category: how to generate random numbers in java within range
*/
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.println("Enter minimum number");
int minimum=in.nextInt();
System.out.println("Enter maximum number");
int maximum=in.nextInt();
int randomNum = minimum + (int)(Math.random() * maximum);
System.out.println("Random Number= "+randomNum);
}
}

Output:

Enter minimum number
1
Enter maximum number
10
Random Number=5

Program #3: Java Example program to generate 10 random numbers using Random class within the range of 1 to 100 using for loop.

package com.randomnumbergenerator;
import java.util.Random;
import java.util.Scanner;
public class RandomNumber {
/**
* @Website: www.instanceofjava.com
* @category: how to generate random numbers in java within range
*/
public static void main(String[] args) {
Random randomNumGenerator = new Random();
for (int idx = 1; idx <= 10; ++idx){
int randomInt = randomNumGenerator.nextInt(100);
System.out.println("Random Number= "+randomInt);
}
}
}

Output:

Random Number= 17
Random Number= 3
Random Number= 74
Random Number= 59
Random Number= 81
Random Number= 90
Random Number= 2
Random Number= 32
Random Number= 11
Random Number= 75

How to generate random numbers in java without repetitions

lets see how to generate unique random numbers in java
By using Collections.shuffle();

Program #4: Java Example program to generate 4 random numbers using Random class within the range of 1 to 100 without duplicate / java generate unique random number between 1 and 100

package com.randomnumbergenerator;
public class RandomNumber {
/**
* @Website: www.instanceofjava.com
* @category: how to generate random numbers in java within range
*/
public static void main(String[] args) {
ArrayList<Integer> list = new ArrayList<Integer>();
for (int i=1; i<10; i++) {
list.add(new Integer(i));
}
Collections.shuffle(list);
for (int i=0; i<4; i++) {
System.out.println("Random Number= "+(list.get(i)));
}
}
}
}

Output:

Random Number= 7
Random Number= 3
Random Number= 2
Random Number= 9

Program #5: Java Example program to generate 10 random numbers. random number generator that doesn't repeat java

package com.randomnumbergenerator;
public class RandomNumber {
/**
* @Website: www.instanceofjava.com
* @category: how to generate 10 random numbers in java within range
*/
public static final int SET_SIZE_REQUIRED = 10;
public static final int NUMBER_RANGE = 100;
public static void main(String[] args) {
Random random = new Random();
Set set = new HashSet<Integer>(SET_SIZE_REQUIRED);
while(set.size()< SET_SIZE_REQUIRED) {
while (set.add(random.nextInt(NUMBER_RANGE)) != true)
;
}
assert set.size() == SET_SIZE_REQUIRED;
System.out.println(set);
}
}

Output:

[48, 99, 24, 58, 44, 77, 14, 95, 31, 79]

How to assign multiple classes to one html element

Posted by: Instanceofjava Posted date: 10:19 PM / comment : 0 HTML interview questions

In HTML if we want to apply any styles to any elements we will use cascading style sheets.
By using CSS we can apply styles to an element in HTML
If some style is needed for more than one type of element then we cant make a style and name it and where ever that style is required we can place that style for that element.

So like this it is always possible to apply multiple styles or multiple classes to HTML elements.
We can specify more than one CSS class to an element.
By using class attribute we can specify multiple CSS classes to a single element and all classes must be separated by a space.
For example if we are applying multiple classes to a div tag.
<div class="class1 class2"></div>
Here class is the attribute and class1 and class2 are the two different CSS classes.
Lets take an example of one paragraph element and two css classes
Fist we define a <p> element with no styles.
Second one more <p> element with one style
Third one more <p> element with two styles.
HTML multiple classes

#1: Html example file to show how to assign multiple CSS classes to an HTML element :

<!DOCTYPE html>
<html>
<title>Cascading Style Sheet</title>
<style type="text/css">
.class1 {
text-align: center;
color: red;
}
.class2 { font-size: 300%; }
</style>
</head>
<body>
<p > How to assign multiple classes to html element<p>
<p class="class1">How to assign multiple classes to html element<p>
<p class="class1 class2">How to assign multiple classes to html element<p>
</body>
</html>

Builder design pattern in java with example program

Posted by: Instanceofjava Posted date: 10:31 PM / comment : 0 java design pattern interview questions and answers , java programming interview questions

Design patterns are solutions to software design problems.
Design patterns classified into three types.
Creational, Structural and behavioral design patterns.

Creational patterns helps us to create objects in a manner suitable to the given situation.
Builder design pattern is one of the creational design pattern in java.
Builder design pattern helps us to create complex class object.
Builder design pattern helps us to separate the construction process of a complex object from its representation so that same object construction process can be created in different representations.
Means it will separate complex construction into two parts initialization of class instance and return class instance.
When a class having more number of fields and constructor of that class take care of assigning initial values.
And when we want to create object of the class we need to pass all parameters and should be in same order which constructor is accepting.
Builder design pattern helps us to create same class object by passing required number of fields by using separate builder class object.
Builder design pattern is useful when object creation is very complex.

Advantages of builder design pattern:

Builder design pattern simplifies complex object creation.
Builder design pattern provides separation between instance creation and representation
Re usability

Program #1: Builder design pattern in java with example program

Employee:

package com.designpatternsinjava.builderdesignpattern;
public class Employee {
String name;
String company;
int id;
String passport_number;
String temp_address;
String perm_address;
int salary;
Employee(String name,String company,int id,String passport_number,String
temp_address,String perm_address,int salary){
this.name=name;
this.company=company;
this.id=id;
this.passport_number=passport_number;
this.temp_address=temp_address;
this.perm_address=perm_address;
this.salary=salary;
}
public String toString(){
return "Name="+name+" \n Company="+company+"\n id="+id+"\n
passport_number="+passport_number+"" +"\n temp_address="+temp_address+"\n
perm_address"+perm_address+"\n
salary="+salary;
}
}

EmployeeBuilder

package com.designpatternsinjava.builderdesignpattern;
public class EmployeeBuilder {
String name;
String company;
int id;
String passport_number;
String temp_address;
String perm_address;
int salary;
public EmployeeBuilder setName(String name) {
this.name = name;
return this;
}
public EmployeeBuilder setCompany(String company) {
this.company = company;
return this;
}
public EmployeeBuilder setId(int id) {
this.id = id;
return this;
}
public EmployeeBuilder setPassport_number(String passport_number) {
this.passport_number = passport_number;
return this;
}
public EmployeeBuilder setTemp_address(String temp_address) {
this.temp_address = temp_address;
return this;
}
public EmployeeBuilder setPerm_address(String perm_address) {
this.perm_address = perm_address;
return this;
}
public EmployeeBuilder setSalary(int salary) {
this.salary = salary;
return this;
}
public Employee build(){
return new Employee(name, company, id, passport_number, temp_address,
perm_address, salary);
}
}

BuilderDemo

To create object of employee class we need to provide all the fields values to the constructor.
So it is somewhat difficult to pass all values all times.
Employee builder class taken all variables of Employee and in setter methods accepts a value and returns EmployeBuilder object.
And EmployeBuilder class has build method which will assign all values to employee and returns Employee object.
Employee empobj= new EmployeeBuilder().setName("Saidesh").setId(1234).build();
Now we create object of Employee class by creating EmployeBuilder class object and caling calling setter methods whatever we have.
Is is very easy to set the values because we have corresponding setter method name is same as variable name.
After setting the values we need to call build method so that it will return employee object with values.

Static method vs final static method in java with example programs

Posted by: Instanceofjava Posted date: 7:36 PM / comment : 4 Core java Interview Questions , java programming interview questions

Static methods are class level so there are not part of object.
So we can not override static methods but we can call super class static method using subclass name or instance also.
If we are trying to override static methods in sub class from super class then it will be method hiding not method overriding.

Means whenever we call the static method on super class will call super class static method and if we are calling method using sub class it will call sub class method.
So it is clear that static methods are hidden not overridden and they are part of class means class level not object level.
Now the question is can a method be static and final together?
For non static methods if we declare it as final then we are preventing that method from overriding so it can not be overridden in sub class.
When we declare static method as final its prevents from method hiding.
When we declare final static method and override in sub class then compiler shows an error
Compile time error: Cannot override the final method from Super
Lets see an example program to understand this better.

Static methods in java

Program #1: Java example program to explain about static method in java

package inheritanceInterviewPrograms;
/*
* @website: www.instanceofjava.com
* @category: Deference between staic and final static methods in java
*/
public class Super {
static void method(){
System.out.println("Super class method");
}
}

package inheritanceInterviewPrograms;
// www.instanceofjava.com
public class Sub extends Super {
static void method(){
System.out.println("Sub class method");
}
public static void main (String args[]) {
Super.method();
Sub.method();
}
}

Output:

Super class method
Sub class method

When we override static methods its not overriding it is method hiding and whenever we call method on class name it will call corresponding class method.
If we call methods using objects it will call same methods.

Program #2: Java example program to explain about calling super class static method using sub class in java

package inheritanceInterviewPrograms;
/*
* @website: www.instanceofjava.com
* @category: Deference between staic and final static methods in java
*/
public class Super {
static void method(){
System.out.println("Super class method");
}
}

package inheritanceInterviewPrograms;
// www.instanceofjava.com
public class Sub extends Super {
public static void main (String args[]) {
Super.method();
Sub.method();
}
}

Output:

Super class method
Super class method

We can call super class static methods using sub class object or sub class name also.
Now lets see what will happen in final static methods

Final static methods in java:

Can a method be static and final together in java?
When we declare a method as final we can not override that method in sub class.
In the same way when we declare a static method as final we can not hide it in sub class means we can not create same method in sub class.
If we try to create same static method in sub class compiler will throw an error.
Lets see a java example program on final static methods in inheritance.

Program #3: Java example program to explain about final static method in java

package inheritanceInterviewPrograms;
/*
* @website: www.instanceofjava.com
* @category: Deference between staic and final static methods in java
*/
public class Super {
final static void method(){
System.out.println("Super class method");
}
}

package inheritanceInterviewPrograms;
// www.instanceofjava.com
public class Sub extends Super {
static void method(){ // compiler time error:
System.out.println("Sub class method");
}
public static void main (String args[]) {
Super.method();
Sub.method();
}
}

Output:

difference between static method and final method in java

Difference between float and double java

Posted by: Instanceofjava Posted date: 4:55 PM / comment : 0 java programming interview questions

Float data type in java is represented in 32 bits, with 1 sign bit, 8 bits of exponent, and 23 bits of the mantissa

Where as Double is is represented in 64 bits, with 1 sign bit, 11 bits of exponent, and 52 bits of mantissa.
Default value of float is 0.0f.
Default value of double is 0.0d.
Floating points numbers also known as real numbers and in java there are two types of floating point one is float and another one is double.

In Java, both double ;and float are used for storing decimal numbers, but they are not the same in the following ways:

	float	double
Size	32-bit (4 bytes)	64-bit (8 bytes)
Precision	~6-7 decimal digits	~15-16 decimal digits
Default Type	No (needs f or F)	Yes (default for decimals)
Performance	Faster on some processors	Higher precision, may be slower
Range	±3.4 × 10³⁸	±1.8 × 10³⁰⁸
Usage	When memory is a concern	When high precision is needed

When to Use:

Use float when dealing with graphics or in game development when memory savings are more significant than precision.
Use double for scientific calculations, financial applications, or whenever high precision is critical.

Float specifies single precision and double specifies double precision.
According to the IEEE standards, float is a 32 bit representation of a real number while double is a 64 bit representation
Normally we use double instead of float to avoid common overflow of range of numbers
Check below diagram for width and range of float and double data types

When do you use float and when do you use double:

Use double data type for all your calculations and temp variables.
Use float when you need to maintain an array of numbers - float[] array (if precision is sufficient), and you are dealing with over tens of thousands of float numbers.
Most of the math functions or operators convert/return double, and you don't want to cast the numbers back to float for any intermediate steps.

How many significant digits have floats and doubles in java?

In java float can handle about 7 decimal places.
And double can handle about 16 decimal places

Program #1: write a java example program which explains differences between float and double in java

package com.instanceofjava.floatvsdouble;
import java.math.BigDecimal;
public class FloatVsDouble {
/**
* @website: www.instanceofjava.com
* @category: float vs double in java with example program
*/
public static void main(String[] args) {
float a=10.8632667283322234f;
double b=10.8632667283322234f;
System.out.println("float value="+a);
System.out.println("double value="+b);
b=10.8632667283322234d;
System.out.println("float value="+a);
System.out.println("double value="+b);
}
}

Output:

float value=10.863267
double value=10.863266944885254
float value=10.863267
double value=10.863266728332224

Difference between float and double java

How to open a webpage using java code

Posted by: Instanceofjava Posted date: 1:14 PM / comment : 1 java programming interview questions

We can open a website or web page using java.
By calling browse() method of java.awt.Desktop.getDesktop() and passing required webpage url as an URI.
In order to make URI create a object fro java.net.uri class objet by passing URL of the web page which need to open
java.awt.Desktop.getDesktop().browse(uri);
Lets see a java program on how to open website url.

Program #1: Simple Java Program to open a website or webpage using java.awt.Desktop

package com.instanceofjava.openwebpage;
import java.awt.Desktop;
import java.io.File;
import java.io.IOException;
import java.net.URI;
public class OpenVLCPlayer {
/**
* @website: www.instanceofjava.com
* @category: how to open a webpage in browser using java code
*/
public static void main(String[] args) {
try {
URI uri= new URI("http://www.instanceofjava.com");
java.awt.Desktop.getDesktop().browse(uri);
System.out.println("Web page opened in browser");
} catch (Exception e) {
e.printStackTrace();
}
}
}

Output:

Web page opened in browser

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