hereral/Clara-Training-Data huggingface dataset:
Question: What are the Constructors of the Class SimpleDateFormat?

Answer: SimpleDateFormat(String pattern_args): Instantiates the SimpleDateFormat class using the provided pattern - pattern_args, default date format symbols for the default FORMAT locale.

SimpleDateFormat(String pattern_args, Locale locale_args): Instantiates the SimpleDateFormat class using the provided pattern - pattern_args. For the provided FORMAT Locale, the default date format symbols are - locale_args.

SimpleDateFormat(String pattern_args, DateFormatSymbols formatSymbols): Instantiates the SimpleDateFormat class and using the provided pattern - pattern_args and the date formatSymbols.
Question: How to get the Current Date and Time in Java?
Answer: There are many ways to get current the date and time in Java. There are many classes that can be used to get current date and time in Java.

1.java.time.format.DateTimeFormatter class
2.java.text.SimpleDateFormat class
3.java.time.LocalDate class
4.java.time.LocalTime class
5.java.time.LocalDateTime class
6.java.time.Clock class
7.java.util.Date class
8.java.sql.Date class
9.java.util.Calendar class
Question: What is Get Current Date and Time: java.time.format.DateTimeFormatter?

Answer: The LocalDateTime.now() method returns the instance of LocalDateTime class. If we print the instance of LocalDateTime class, it prints the current date and time. To format the current date, you can use DateTimeFormatter class which is included in JDK 1.8.
Question: Can you provide an example of Get Current Date: java.text.SimpleDateFormat?

Answer: import java.text.SimpleDateFormat;  
import java.util.Date;  
public class CurrentDateTimeExample2 {  
public static void main(String[] args) {  
    SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");  
    Date date = new Date();  
    System.out.println(formatter.format(date));  
}  
}  
Output: 06/11/2017 12:26:18
Question: Can you provide an example of Get Current Date: java.time.LocalDate ?

Answer: // important import statements  
import java.time.LocalDateTime;  
import java.time.format.DateTimeFormatter;  
    
public class CurrentDateTimeExample3   
{      
  // main method  
  public static void main(String[] argvs)   
  {      
        System.out.println(java.time.LocalDate.now());    
  }      
}  
Output: 2021-12-17
Question: Can you provide an example of Get Current Date: java.time.LocalTime?
Answer: // important import statements  
import java.time.LocalDateTime;  
import java.time.format.DateTimeFormatter;  
    
public class CurrentDateTimeExample4   
{      
  // main method  
  public static void main(String[] argvs)   
  {      
        System.out.println(java.time.LocalTime.now());    
  }      
}  
Output: 15:55:10.424178667
Question: Can you provide an example of Get Current Date: java.time.LocalDateTime?

Answer: // important import statements  
import java.time.LocalDateTime;  
import java.time.format.DateTimeFormatter;  
    
public class CurrentDateTimeExample5   
{      
  // main method  
  public static void main(String[] argvs)   
  {      
        System.out.println(java.time.LocalDateTime.now());    
  }      
}  
Output: 2021-12-17T15:59:19.516010365
Question: Can you provide an example of Get Current Date: java.time.Clock?
Answer: // important import statements  
import java.time.LocalDateTime;  
import java.time.format.DateTimeFormatter;  
    
public class CurrentDateTimeExample6   
{      
  // main method  
  public static void main(String[] argvs)   
  {      
    System.out.println(java.time.Clock.systemUTC().instant());    
  }      
}  
Output: 2021-12-17T16:04:03.930224479Z
Question: Can you provide an example of Get Current Date: java.util.Date?

Answer: // important import statements  
import java.time.LocalDateTime;  
import java.time.format.DateTimeFormatter;  
    
public class CurrentDateTimeExample7   
{      
  // main method  
  public static void main(String[] argvs)   
  {      
    // creating a new object of the class Date  
    java.util.Date date = new java.util.Date();    
    System.out.println(date);   
       
  }      
}  
Output: Fri Dec 17 16:07:15 GMT 2021
Question: Can you provide an example of Get Current Date: java.sql.Date?

Answer: // important import statements  
import java.time.LocalDateTime;  
import java.time.format.DateTimeFormatter;  
    
public class CurrentDateTimeExample9   
{      
  // main method  
  public static void main(String[] argvs)   
  {   
    long millis=System.currentTimeMillis();  
      
    // creating a new object of the class Date  
    java.sql.Date date = new java.sql.Date(millis);       
    System.out.println(date);   
        
       
  }      
}  
Output: 2021-12-17
Question: Can you provide an example of Get Current Date: java.util.Calendar?

Answer: // important import statements  
import java.time.LocalDateTime;  
import java.time.format.DateTimeFormatter;  
    
public class CurrentDateTimeExample10   
{      
  // main method  
  public static void main(String[] argvs)   
  {   
    long millis=System.currentTimeMillis();  
      
    // creating a new object of the class Date  
    java.sql.Date date = new java.sql.Date(millis);       
    System.out.println(date);   
        
       
  }      
}  
Output: Fri Dec 17 19:23:10 GMT 2021
Question: What is Java Convert String to int?

Answer: We can convert String to an int in java using Integer.parseInt() method. To convert String into Integer, we can use Integer.valueOf() method which returns instance of Integer class.
Question: Can you provide an example of Java String to int: Integer.parsenInt()?

Answer: //Java Program to demonstrate the conversion of String into int  
//using Integer.parseInt() method  
public class StringToIntExample1{  
public static void main(String args[]){  
//Declaring String variable  
String s="200";  
//Converting String into int using Integer.parseInt()  
int i=Integer.parseInt(s);  
//Printing value of i  
System.out.println(i);  
}}  
Output: 200
Question: How to Convert Java int to String?

Answer: We can convert int to String in java using String.valueOf() and Integer.toString() methods. Alternatively, we can use String.format() method, string concatenation operator etc.
Question: Can you provide an example of Java int to String using String.valueOf()?

Answer: //Java Program to demonstrate the conversion of String into Integer  
//using Integer.valueOf() method  
public class StringToIntegerExample2{  
public static void main(String args[]){  
//Declaring a string  
String s="200";  
//converting String into Integer using Integer.valueOf() method  
Integer i=Integer.valueOf(s);  
System.out.println(i);  
}}  
Output: 300
Question: How to Convert Java String to long?

Answer: We can convert String to long in java using Long.parseLong() method.
Question: Can you provide an example of Java String to long?

Answer: public class StringToLongExample{  
public static void main(String args[]){  
String s="9990449935";  
long l=Long.parseLong(s);  
System.out.println(l);  
}}  
Output: 9990449935
Question: How to convert Java long to String?

Answer: We can convert long to String in java using String.valueOf() and Long.toString() methods.
Question: Can you provide an example of Java long to String using String.valueOf()?

Answer: public class LongToStringExample1{  
public static void main(String args[]){  
long i=9993939399L;  
String s=String.valueOf(i);  
System.out.println(s);  
}}  
Output: 9993939399
Question: How to convert Java String to float?

Answer: We can convert String to float in java using
Question: Can you provide an example of Java string to float?

Answer: public class StringToFloatExample{  
public static void main(String args[]){  
String s="23.6";  
float f=Float.parseFloat("23.6");  
System.out.println(f);  
}}  
Output: 23.6
Question: How to convert Java float to String?

Answer: We can convert float to String in java using String.valueOf() and Float.toString() methods.
Question: Can you provide an example of Java float to String using String.valueOf()?

Answer: public class FloatToStringExample1{  
public static void main(String args[]){  
float f=12.3F;//F is the suffix for float  
String s=String.valueOf(f);  
System.out.println(s);  
}}  
Output: 12.3
Question: How to convert Java String to double?

Answer: We can convert String to double in java using Double.parseDouble() method.
Question: Can you provide an example of Java String to double?

Answer: public class StringToDoubleExample{  
public static void main(String args[]){  
String s="23.6";  
double d=Double.parseDouble("23.6");  
System.out.println(d);  
}}  
Output: 23.6
Question: How to convert Java double to String?

Answer: We can convert double to String in java using String.valueOf() and Double.toString() methods.
Question: Can you provide an example of Java double to String using String.valueOf()?

Answer: public class DoubleToStringExample1{  
public static void main(String args[]){  
double d=12.3;  
String s=String.valueOf(d);  
System.out.println(s);  
}}  
Output: 12.3
Question: How to convert Java String to charHow?

Answer: We can convert String to char in java using charAt() method of String class.

Java Convert String to char
The charAt() method returns a single character only. To get all characters, you can use loop.
Question: Can you provide an example of Java string to char: charAt() method?

Answer: public class StringToCharExample1{  
public static void main(String args[]){  
String s="hello";  
char c=s.charAt(0);//returns h  
System.out.println("1st character is: "+c);  
}}  
Output: 1st character is: h
Question: How to convert Java char to String?

Answer: We can convert String to char in java using charAt() method of String class.

Java Convert String to char
The charAt() method returns a single character only. To get all characters, you can use loop.
Question: Can you provide an example of Java char to String using String.valueOf() method?

Answer: public class CharToStringExample1{  
public static void main(String args[]){  
char c='S';  
String s=String.valueOf(c);  
System.out.println("String is: "+s);  
}}  
Output: String is: S
Question: How to convert Java String to Object?

Answer: We can convert String to Object in java with assignment operator. Each class is internally a child class of Object class. So you can assign string to Object directly.
Question: Can you provide an example of Java String to Object?

Answer: public class StringToObjectExample{  
public static void main(String args[]){  
String s="hello";  
Object obj=s;  
System.out.println(obj);  
}}  
Output: hello
Question: How to convert Java Object to String?

Answer: We can convert Object to String in java using toString() method of Object class or String.valueOf(object) method.
Question: Can you provide an example of Java Object to String using Converting User-defined class?

Answer: class Emp{}  
public class ObjectToStringExample{  
public static void main(String args[]){  
Emp e=new Emp();  
String s=e.toString();  
String s2=String.valueOf(e);  
System.out.println(s);  
System.out.println(s2);  
}}  
Output:
Question: How to convert Java int to long?

Answer: We can convert int to long in java using assignment operator. There is nothing to do extra because lower type can be converted to higher type implicitly.
Question: Can you provide an example of Java int to long?

Answer: public class IntToLongExample1{  
public static void main(String args[]){  
int i=200;  
long l=i;  
System.out.println(l);  
}}
Question: How to convert Java long to int?

Answer: We can convert long to int in java using typecasting. To convert higher data type into lower, we need to perform typecasting.

Typecasting in java is performed through typecast operator (datatype).

Here, we are going to learn how to convert long primitive type into int and Long object into int.
Question: Can you provide an example of Java long to int?

Answer: public class LongToIntExample2{  
public static void main(String args[]){  
Long l= new Long(10);  
int i=l.intValue();  
System.out.println(i);  
}}  
Output:
Question: How to convert Java int to double?

Answer: We can convert int to double in java using assignment operator. There is nothing to do extra because lower type can be converted to higher type implicitly.
Question: Can you provide an example of Java int to double?

Answer: public class IntToDoubleExample1{  
public static void main(String args[]){  
int i=200;  
double d=i;  
System.out.println(d);  
}}  
Output:
Question: How to convert Java double to int?

Answer: We can convert double to int in java using typecasting. To convert double data type into int, we need to perform typecasting.
Question: Can you provide an example of Java double to int: Typecasting?

Answer: public class DoubleToIntExample1{  
public static void main(String args[]){  
double d=10.5;  
int i=(int)d;  
System.out.println(i);  
}}  

Output:
Question: How to convert Java char to int?

Answer: We can convert char to int in java using various ways. If we direct assign char variable to int, it will return ASCII value of given character.
Question: Java char to int Example: Get ASCII value
Answer: public class CharToIntExample1{  
public static void main(String args[]){  
char c='a';  
char c2='1';  
int a=c;  
int b=c2;  
System.out.println(a);  
System.out.println(b);  
}}  
Output: 97
49
Question: How to convert Java int to char?

Answer: We can convert int to char in java using typecasting. To convert higher data type into lower, we need to perform typecasting. Here, the ASCII character of integer value will be stored in the char variable.
Question: Can you provide an example of Java int to char?

Answer: public class IntToCharExample1{  
public static void main(String args[]){  
int a=65;  
char c=(char)a;  
System.out.println(a);  
}}  
Output: A
Question: How to convert Java String to boolean?

Answer: We can convert String to boolean in java using Boolean.parseBoolean(string) method.

To convert String into Boolean object, we can use Boolean.valueOf(string) method which returns instance of Boolean class.

To get boolean true, string must contain "true". Here, case is ignored. So, "true" or "TRUE" will return boolean true. Any other string value except "true" returns boolean false.
Question: Can you provide an example of Java String to boolean using Boolean.parseBoolean()?

Answer: public class StringToBooleanExample{  
public static void main(String args[]){  
String s1="true";  
String s2="TRue";  
String s3="ok";  
boolean b1=Boolean.parseBoolean(s1);  
boolean b2=Boolean.parseBoolean(s2);  
boolean b3=Boolean.parseBoolean(s3);  
System.out.println(b1);  
System.out.println(b2);  
System.out.println(b3);  
}}  
Test it Now
Output: true
true
false
Question: How to convert Java boolean to String?

Answer: We can convert boolean to String in java using String.valueOf(boolean) method.

Alternatively, we can use Boolean.toString(boolean) method which also converts boolean into String.
Question: Can you provide an example of Java boolean to String using String.valueOf()?
Answer: public class BooleanToStringExample1{  
public static void main(String args[]){  
boolean b1=true;  
boolean b2=false;  
String s1=String.valueOf(b1);  
String s2=String.valueOf(b2);  
System.out.println(s1);  
System.out.println(s2);  
}}  
Output: true
false
Question: How to convert Java Date to Timestamp?

Answer: We can convert Date to Timestamp in java using constructor of java.sql.Timestamp class.

The constructor of Timestamp class receives long value as an argument. So you need to convert date into long value using getTime() method of java.util.Date class.

You can also format the output of Timestamp using java.text.SimpleDateFormat class.
Question: Can you provide an example of Java Date to Timestamp?

Answer: import java.sql.Timestamp;    
import java.util.Date;    
 public class DateToTimestampExample1 {    
       public static void main(String args[]){    
                Date date = new Date();  
                Timestamp ts=new Timestamp(date.getTime());  
                System.out.println(ts);                     
        }    
}    

Output: 2017-11-02 01:59:30.274
Question: How to convert Java Timestamp to Date?

Answer: We can convert Timestamp to Date in java using constructor of java.util.Date class.

The constructor of Date class receives long value as an argument. So, you need to convert Timestamp object into long value using getTime() method of java.sql.Timestamp class.

Let's see the constructor of Date class and signature of getTime() method.
Question: Can you provide an example of Java Timestamp to Date?

Answer: import java.sql.Timestamp;    
import java.util.Date;    
 public class TimestampToDateExample1 {    
       public static void main(String args[]){    
                Timestamp ts=new Timestamp(System.currentTimeMillis());  
                Date date=new Date(ts.getTime());  
                System.out.println(date);                     
        }    
}    
Output:
Question: How to convert Binary to Decimal?

Answer: We can convert binary to decimal in java using Integer.parseInt() method or custom logic.
Question: How to convert Java Binary to Decimals using Integer.parseInt()?

Answer: We can convert binary to decimal in java using Integer.parseInt() method or custom logic.
Question: How to convert Decimal to Binary?

Answer: We can convert decimal to binary in java using Integer.toBinaryString() method or custom logic.
Question: How to convert Java Decimal to Binary using conversion: Integer.toBinaryString()?

Answer: The Integer.toBinaryString() method converts decimal to binary string. The signature of toBinaryString() method is given below:
Question: How to convert Hexadecimal to Decimal?

Answer: We can convert hexadecimal to decimal in java using Integer.parseInt() method or custom logic.
Question: What is Java Hexadecimal to Decimal conversion: Integer.parseInt()?

Answer: The Integer.parseInt() method converts string to int with given redix. The signature of parseInt() method is given below:
Question: How to convert Java Decimal to Hexadecimal?

Answer: We can convert decimal to hexadecimal in java using Integer.toHexString() method or custom logic.
Question: How to convert Java Decimal to Hex using Interger.toHexString() method?

Answer: The Integer.toHexString() method converts decimal to hexadecimal. The signature of toHexString() method is given below:

public static String toHexString(int decimal)
Question: How to convert Java Octal to Decimal?

Answer: We can convert octal to decimal in java using Integer.parseInt() method or custom logic.
Question: How to convert Java Octal to Decimal conversion: Integer.parsenInt()?

Answer: he Integer.parseInt() method converts a string to an int with the given radix. If you pass 8 as a radix, it converts an octal string into decimal. Let us see the signature of parseInt() method:
Question: How to convert Java Decimal to Octal?

Answer: We can convert decimal to octal in java using Integer.toOctalString() method or custom logic.
Question: Java Decimal to Octal conversion: Integer.toOctalString() 

Answer: The Integer.toOctalString() method converts decimal to octal string. The signature of toOctalString() method is given below:

public static String toOctalString(int decimal)
Question: What is Collections in Java?

Answer: The Collection in Java is a framework that provides an architecture to store and manipulate the group of objects.

Java Collections can achieve all the operations that you perform on a data such as searching, sorting, insertion, manipulation, and deletion.


Java Collection means a single unit of objects. Java Collection framework provides many interfaces (Set, List, Queue, Deque) and classes (ArrayList, Vector, LinkedList, PriorityQueue, HashSet, LinkedHashSet, TreeSet).
Question: What is Collection in Java?

Answer: A Collection represents a single unit of objects, i.e., a group.
Question: What is a framework in Java?

Answer: It provides readymade architecture.
It represents a set of classes and interfaces.
It is optional.
Question: What is Collection framework?

Answer: The Collection framework represents a unified architecture for storing and manipulating a group of objects. It has:

1. Interfaces and its implementations, i.e., classes
2. Algorithm
Question: What are the Methods of Collection interface?

Answer: Methods of Collection interface
There are many methods declared in the Collection interface. They are as follows:

Method: public boolean add(E e)	
Description: It is used to insert an element in this collection.

Method: public boolean addAll(Collection<? extends E> c)	
Description: It is used to insert the specified collection elements in the invoking collection.

Method: public boolean remove(Object element)	
Description: It is used to delete an element from the collection.

Method: public boolean removeAll(Collection<?> c)	
Description: It is used to delete all the elements of the specified collection from the invoking collection.

Method: default boolean removeIf(Predicate<? super E> filter)	
Description: It is used to delete all the elements of the collection that satisfy the specified predicate.

Method: public boolean retainAll(Collection<?> c)	
Description: It is used to delete all the elements of invoking collection except the specified collection.

Method: public int size()	
Description: It returns the total number of elements in the collection.

Method: public void clear()	
Description: It removes the total number of elements from the collection.

Method: public boolean contains(Object element)	
Description: It is used to search an element.

Method: public boolean containsAll(Collection<?> c)	
Description: It is used to search the specified collection in the collection.

Method: public Iterator iterator()	
Description: It returns an iterator.

Method: public Object[] toArray()	
Description: It converts collection into array.

Method: public <T> T[] toArray(T[] a)	
Description: It converts collection into array. Here, the runtime type of the returned array is that of the specified array.

Method: public boolean isEmpty()	
Description: It checks if collection is empty.

Method: default Stream<E> parallelStream()	
Description: It returns a possibly parallel Stream with the collection as its source.

Method: default Stream<E> stream()	
Description: It returns a sequential Stream with the collection as its source.

Method: default Spliterator<E> spliterator()	
Description: It generates a Spliterator over the specified elements in the collection.

Method: public boolean equals(Object element)	
Description: It matches two collections.

Method: public int hashCode()	
Description: It returns the hash code number of the collection.
Question: What is Iterator interface?


Answer: Iterator interface provides the facility of iterating the elements in a forward direction only.
Question: What are the Methods of Iterator interface?

Answer: Methods of Iterator interface
There are only three methods in the Iterator interface. They are:

Method:	public boolean hasNext()	
Description:It returns true if the iterator has more elements otherwise it returns false.

Method:	public Object next()	
Description:It returns the element and moves the cursor pointer to the next element.

Method:	public void remove()	
Description:It removes the last elements returned by the iterator. It is less used.
Question: What is iterable Interface?

Answer: he Iterable interface is the root interface for all the collection classes. The Collection interface extends the Iterable interface and therefore all the subclasses of Collection interface also implement the Iterable interface.

It contains only one abstract method. i.e.,

Iterator<T> iterator()  
It returns the iterator over the elements of type T.
Question: What is Collection Interface?

Answer: The Collection interface is the interface which is implemented by all the classes in the collection framework. It declares the methods that every collection will have. In other words, we can say that the Collection interface builds the foundation on which the collection framework depends.

Some of the methods of Collection interface are Boolean add ( Object obj), Boolean addAll ( Collection c), void clear(), etc. which are implemented by all the subclasses of Collection interface.
Question: What is Java ArrayList?

Answer: Java ArrayList class uses a dynamic array for storing the elements. It is like an array, but there is no size limit. We can add or remove elements anytime. So, it is much more flexible than the traditional array. It is found in the java.util package. It is like the Vector in C++.

The ArrayList in Java can have the duplicate elements also. It implements the List interface so we can use all the methods of the List interface here. The ArrayList maintains the insertion order internally.

It inherits the AbstractList class and implements List interface. 

The important points about the Java ArrayList class are:

Java ArrayList class can contain duplicate elements.
Java ArrayList class maintains insertion order.
Java ArrayList class is non synchronized.
Java ArrayList allows random access because the array works on an index basis.
In ArrayList, manipulation is a little bit slower than the LinkedList in Java because a lot of shifting needs to occur if any element is removed from the array list.
We can not create an array list of the primitive types, such as int, float, char, etc. It is required to use the required wrapper class in such cases. For example:

ArrayList<int> al = ArrayList<int>(); // does not work  
ArrayList<Integer> al = new ArrayList<Integer>(); // works fine
Question: What is the class declaration for ArrayList class?

Answer: Let's see the declaration for java.util.ArrayList class.

public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, Serializable
Question: What are the Constructors of the  ArrayList?

Answer: Constructors of ArrayList

Constructor: ArrayList()	
Description: It is used to build an empty array list.

Constructor: ArrayList(Collection<? extends E> c)	
Description: It is used to build an array list that is initialized with the elements of the collection c.

Constructor: ArrayList(int capacity)	
Description: It is used to build an array list that has the specified initial capacity.
Question: What are the differences between Java Non-generic and Generic Collection?

Answer: Java collection framework was non-generic before JDK 1.5. Since 1.5, it is generic.

Java new generic collection allows you to have only one type of object in a collection. Now it is type-safe, so typecasting is not required at runtime.

Let's see the old non-generic example of creating a Java collection.

ArrayList list=new ArrayList();//creating old non-generic arraylist  

Let's see the new generic example of creating java collection.

ArrayList<String> list=new ArrayList<String>();//creating new generic arraylist  
In a generic collection, we specify the type in angular braces. Now ArrayList is forced to have the only specified type of object in it. If you try to add another type of object, it gives a compile-time error.
Question: Can you provide an example of Java ArrayList?

Answer: FileName: ArrayListExample1.java

import java.util.*;  
 public class ArrayListExample1{  
 public static void main(String args[]){  
  ArrayList<String> list=new ArrayList<String>();//Creating arraylist    
      list.add("Mango");//Adding object in arraylist    
      list.add("Apple");    
      list.add("Banana");    
      list.add("Grapes");    
      //Printing the arraylist object   
      System.out.println(list);  
 }  
}  

Output:

[Mango, Apple, Banana, Grapes]
Question: How to Sort ArrayList?

Answer: The java.util package provides a utility class Collections, which has the static method sort(). Using the Collections.sort() method, we can easily sort the ArrayList.

import java.util.*;  
class SortArrayList{  
 public static void main(String args[]){  
  //Creating a list of fruits  
  List<String> list1=new ArrayList<String>();  
  list1.add("Mango");  
  list1.add("Apple");  
  list1.add("Banana");  
  list1.add("Grapes");  
  //Sorting the list  
  Collections.sort(list1);  
   //Traversing list through the for-each loop  
  for(String fruit:list1)  
    System.out.println(fruit);  
      
 System.out.println("Sorting numbers...");  
  //Creating a list of numbers  
  List<Integer> list2=new ArrayList<Integer>();  
  list2.add(21);  
  list2.add(11);  
  list2.add(51);  
  list2.add(1);  
  //Sorting the list  
  Collections.sort(list2);  
   //Traversing list through the for-each loop  
  for(Integer number:list2)  
    System.out.println(number);  
 }  
   
}  

Output:
Apple
Banana
Grapes
Mango
Sorting numbers...
1
11
21
51
Question: What are the ways to iterate the elements of the collection in Java?

Answer: There are various ways to traverse the collection elements:

1.By Iterator interface.
2.By for-each loop.
3.By ListIterator interface.
4.By for loop.
5.By forEach() method.
6.By forEachRemaining() method.
Question: Can you provide an example of traversing the ArrayList elements?

Answer: Let's see an example to traverse the ArrayList elements through other ways

FileName: ArrayList4.java

import java.util.*;  
class ArrayList4{  
 public static void main(String args[]){  
    ArrayList<String> list=new ArrayList<String>();//Creating arraylist  
           list.add("Ravi");//Adding object in arraylist  
           list.add("Vijay");  
           list.add("Ravi");  
           list.add("Ajay");  
            
           System.out.println("Traversing list through List Iterator:");  
           //Here, element iterates in reverse order  
              ListIterator<String> list1=list.listIterator(list.size());  
              while(list1.hasPrevious())  
              {  
                  String str=list1.previous();  
                  System.out.println(str);  
              }  
        System.out.println("Traversing list through for loop:");  
           for(int i=0;i<list.size();i++)  
           {  
            System.out.println(list.get(i));     
           }  
              
        System.out.println("Traversing list through forEach() method:");  
        //The forEach() method is a new feature, introduced in Java 8.  
            list.forEach(a->{ //Here, we are using lambda expression  
                System.out.println(a);  
              });  
                
            System.out.println("Traversing list through forEachRemaining() method:");  
              Iterator<String> itr=list.iterator();  
              itr.forEachRemaining(a-> //Here, we are using lambda expression  
              {  
            System.out.println(a);  
              });  
 }  
}  

Output:

Traversing list through List Iterator:
Ajay
Ravi
Vijay
Ravi
Traversing list through for loop:
Ravi
Vijay
Ravi
Ajay
Traversing list through forEach() method:
Ravi
Vijay
Ravi
Ajay
Traversing list through forEachRemaining() method:
Ravi
Vijay
Ravi
Ajay
Question: Can you provide an example of User-defined class objects in Java ArrayList?
Answer: Let's see an example where we are storing Student class object in an array list.

FileName: ArrayList5.java
class Student{  
  int rollno;  
  String name;  
  int age;  
  Student(int rollno,String name,int age){  
   this.rollno=rollno;  
   this.name=name;  
   this.age=age;  
  }  
}  

import java.util.*;  
 class ArrayList5{  
 public static void main(String args[]){  
  //Creating user-defined class objects  
  Student s1=new Student(101,"Sonoo",23);  
  Student s2=new Student(102,"Ravi",21);  
  Student s2=new Student(103,"Hanumat",25);  
  //creating arraylist  
  ArrayList<Student> al=new ArrayList<Student>();  
  al.add(s1);//adding Student class object  
  al.add(s2);  
  al.add(s3);  
  //Getting Iterator  
  Iterator itr=al.iterator();  
  //traversing elements of ArrayList object  
  while(itr.hasNext()){  
    Student st=(Student)itr.next();  
    System.out.println(st.rollno+" "+st.name+" "+st.age);  
  }  
 }  
}  

Output:
      101 Sonoo 23
       102 Ravi 21
       103 Hanumat 25
Question: Can you provide an example of Java ArrayList Serialization and Deserialization?

Answer: Let's see an example to serialize an ArrayList object and then deserialize it.

FileName: ArrayList6.java

import java.io.*;  
import java.util.*;  
 class ArrayList6 {  
  
        public static void main(String [] args)  
        {  
          ArrayList<String> al=new ArrayList<String>();  
          al.add("Ravi");    
          al.add("Vijay");    
          al.add("Ajay");    
            
          try  
          {  
              //Serialization  
              FileOutputStream fos=new FileOutputStream("file");  
              ObjectOutputStream oos=new ObjectOutputStream(fos);  
              oos.writeObject(al);  
              fos.close();  
              oos.close();  
              //Deserialization  
              FileInputStream fis=new FileInputStream("file");  
              ObjectInputStream ois=new ObjectInputStream(fis);  
            ArrayList  list=(ArrayList)ois.readObject();  
            System.out.println(list);    
          }catch(Exception e)  
          {  
              System.out.println(e);  
          }  
       }  
    }         

Output:
      [Ravi, Vijay, Ajay]
Question: Can you provide an example of Java ArrayList to add elements?

Answer: Here, we see different ways to add an element.

FileName: ArrayList7.java

import java.util.*;  
 class ArrayList7{  
 public static void main(String args[]){  
  ArrayList<String> al=new ArrayList<String>();  
           System.out.println("Initial list of elements: "+al);  
           //Adding elements to the end of the list  
           al.add("Ravi");  
           al.add("Vijay");  
           al.add("Ajay");  
           System.out.println("After invoking add(E e) method: "+al);  
           //Adding an element at the specific position  
           al.add(1, "Gaurav");  
           System.out.println("After invoking add(int index, E element) method: "+al);  
           ArrayList<String> al2=new ArrayList<String>();  
           al2.add("Sonoo");  
           al2.add("Hanumat");  
           //Adding second list elements to the first list  
           al.addAll(al2);  
           System.out.println("After invoking addAll(Collection<? extends E> c) method: "+al);  
           ArrayList<String> al3=new ArrayList<String>();  
           al3.add("John");  
           al3.add("Rahul");  
           //Adding second list elements to the first list at specific position  
           al.addAll(1, al3);  
           System.out.println("After invoking addAll(int index, Collection<? extends E> c) method: "+al);  
             
 }  
}  

Output:

Initial list of elements: []
After invoking add(E e) method: [Ravi, Vijay, Ajay]
After invoking add(int index, E element) method: [Ravi, Gaurav, Vijay, Ajay]
After invoking addAll(Collection<? extends E> c) method: 
[Ravi, Gaurav, Vijay, Ajay, Sonoo, Hanumat]
After invoking addAll(int index, Collection<? extends E> c) method: 
[Ravi, John, Rahul, Gaurav, Vijay, Ajay, Sonoo, Hanumat]
Question: Can you provide an example of Java ArrayList to remove elements?

Answer: Here, we see different ways to remove an element.

FileName: ArrayList8.java

import java.util.*;  
 class ArrayList8 {  
  
        public static void main(String [] args)  
        {  
          ArrayList<String> al=new ArrayList<String>();  
          al.add("Ravi");    
          al.add("Vijay");    
          al.add("Ajay");   
          al.add("Anuj");  
          al.add("Gaurav");  
          System.out.println("An initial list of elements: "+al);   
          //Removing specific element from arraylist  
          al.remove("Vijay");  
          System.out.println("After invoking remove(object) method: "+al);   
          //Removing element on the basis of specific position  
          al.remove(0);  
          System.out.println("After invoking remove(index) method: "+al);   
            
          //Creating another arraylist  
          ArrayList<String> al2=new ArrayList<String>();    
          al2.add("Ravi");    
          al2.add("Hanumat");    
          //Adding new elements to arraylist  
          al.addAll(al2);  
          System.out.println("Updated list : "+al);   
          //Removing all the new elements from arraylist  
          al.removeAll(al2);  
          System.out.println("After invoking removeAll() method: "+al);   
          //Removing elements on the basis of specified condition  
          al.removeIf(str -> str.contains("Ajay"));   //Here, we are using Lambda expression   
          System.out.println("After invoking removeIf() method: "+al);  
          //Removing all the elements available in the list  
          al.clear();  
          System.out.println("After invoking clear() method: "+al);   
       }  
    }                   


Output:

An initial list of elements: [Ravi, Vijay, Ajay, Anuj, Gaurav]
After invoking remove(object) method: [Ravi, Ajay, Anuj, Gaurav]
After invoking remove(index) method: [Ajay, Anuj, Gaurav]
Updated list : [Ajay, Anuj, Gaurav, Ravi, Hanumat]
After invoking removeAll() method: [Ajay, Anuj, Gaurav]
After invoking removeIf() method: [Anuj, Gaurav]
After invoking clear() method: []
Question: What are the important points in Java LinkedList class?

Answer: Java LinkedList class uses a doubly linked list to store the elements. It provides a linked-list data structure. It inherits the AbstractList class and implements List and Deque interfaces.

The important points about Java LinkedList are:

-Java LinkedList class can contain duplicate elements.
-Java LinkedList class maintains insertion order.
-Java LinkedList class is non synchronized.
-In Java LinkedList class, manipulation is fast because no shifting needs to occur.
-Java LinkedList class can be used as a list, stack or queue.
Hierarchy of LinkedList class

As shown in the above diagram, Java LinkedList class extends AbstractSequentialList class and implements List and Deque interfaces.
Doubly Linked List

In the case of a doubly linked list, we can add or remove elements from both sides.
Question: What is the class declaration for LinkedList class?

Answer: Let's see the declaration for java.util.LinkedList class.

public class LinkedList<E> extends AbstractSequentialList<E> implements List<E>, Deque<E>, Cloneable, Serializable
Question: What are the Constructors of Java LinkedList?

Answer: Constructor: LinkedList()
Description: It is used to construct an empty list.

Constructor: LinkedList(Collection<? extends E> c)
Description: It is used to construct a list containing the elements of the specified collection, in the order, they are returned by the collection's iterator.
Question: Can you provide an example of Java LinkedList?

Answer: import java.util.*;  
public class LinkedList1{  
 public static void main(String args[]){  
  
  LinkedList<String> al=new LinkedList<String>();  
  al.add("Ravi");  
  al.add("Vijay");  
  al.add("Ravi");  
  al.add("Ajay");  
  
  Iterator<String> itr=al.iterator();  
  while(itr.hasNext()){  
   System.out.println(itr.next());  
  }  
 }  
}  

Output: Ravi
       Vijay
       Ravi
       Ajay
Question: What are the difference between ArrayList and LinkedList?

Answer: ArrayList and LinkedList both implement the List interface and maintain insertion order. Both are non-synchronized classes.

However, there are many differences between the ArrayList and LinkedList classes that are given below.

1)   ArrayList internally uses a dynamic array to store the elements while LinkedList internally uses a doubly linked list to store the elements. 
2) Manipulation with ArrayList is slow because it internally uses an array. If any element is removed from the array, all the other elements are shifted in memory while Manipulation with LinkedList is faster than ArrayList because it uses a doubly linked list, so no bit shifting is required in memory.
3) An ArrayList class can act as a list only because it implements List only while LinkedList class can act as a list and queue both because it implements List and Deque interfaces.
4) ArrayList is better for storing and accessing data while LinkedList is better for manipulating data.
5) The memory location for the elements of an ArrayList is contiguous while The location for the elements of a linked list is not contagious.
6) Generally, when an ArrayList is initialized, a default capacity of 10 is assigned to the ArrayList while  There is no case of default capacity in a LinkedList. In LinkedList, an empty list is created when a LinkedList is initialized.
7)  To be precise, an ArrayList is a resizable array while LinkedList implements the doubly linked list of the list interface.
Question: Can you provide an example of ArrayList and LinkedList in Java?

Answer: Let's see a simple example where we are using ArrayList and LinkedList both.

FileName: TestArrayLinked.java

import java.util.*;    
class TestArrayLinked{    
 public static void main(String args[]){    
     
  List<String> al=new ArrayList<String>();//creating arraylist    
  al.add("Ravi");//adding object in arraylist    
  al.add("Vijay");    
  al.add("Ravi");    
  al.add("Ajay");    
    
  List<String> al2=new LinkedList<String>();//creating linkedlist    
  al2.add("James");//adding object in linkedlist    
  al2.add("Serena");    
  al2.add("Swati");    
  al2.add("Junaid");    
    
  System.out.println("arraylist: "+al);  
  System.out.println("linkedlist: "+al2);  
 }    
}    

Output:
arraylist: [Ravi,Vijay,Ravi,Ajay]
linkedlist: [James,Serena,Swati,Junaid]
Question: What is Java List?

Answer: List in Java provides the facility to maintain the ordered collection. It contains the index-based methods to insert, update, delete and search the elements. It can have the duplicate elements also. We can also store the null elements in the list.

The List interface is found in the java.util package and inherits the Collection interface. It is a factory of ListIterator interface. Through the ListIterator, we can iterate the list in forward and backward directions. The implementation classes of List interface are ArrayList, LinkedList, Stack and Vector. The ArrayList and LinkedList are widely used in Java programming. The Vector class is deprecated since Java 5.
List Interface declaration
public interface List<E> extends Collection<E>
Question: What is Java List and ArrayList?

Answer: List is an interface whereas ArrayList is the implementation class of List.
Question: How to create a List in Java?

Answer: The ArrayList and LinkedList classes provide the implementation of List interface. Let's see the examples to create the List:

//Creating a List of type String using ArrayList  
List<String> list=new ArrayList<String>();  
//Creating a List of type Integer using ArrayList  
List<Integer> list=new ArrayList<Integer>();  
//Creating a List of type Book using ArrayList  
List<Book> list=new ArrayList<Book>();  
//Creating a List of type String using LinkedList  
List<String> list=new LinkedList<String>();  

In short, you can create the List of any type. The ArrayList<T> and LinkedList<T> classes are used to specify the type. Here, T denotes the type.
Question: Can you provide an example of Java List?

Answer: Let's see a simple example of List where we are using the ArrayList class as the implementation.

import java.util.*;  
public class ListExample1{  
public static void main(String args[]){  
 //Creating a List  
 List<String> list=new ArrayList<String>();  
 //Adding elements in the List  
 list.add("Mango");  
 list.add("Apple");  
 list.add("Banana");  
 list.add("Grapes");  
 //Iterating the List element using for-each loop  
 for(String fruit:list)  
  System.out.println(fruit);  
  
}  
}  

Output:
Mango
Apple
Banana
Grapes
Question: How to convert Array to List?

Answer: We can convert the Array to List by traversing the array and adding the element in list one by one using list.add() method. Let's see a simple example to convert array elements into List.

import java.util.*;  
public class ArrayToListExample{  
public static void main(String args[]){  
//Creating Array  
String[] array={"Java","Python","PHP","C++"};  
System.out.println("Printing Array: "+Arrays.toString(array));  
//Converting Array to List  
List<String> list=new ArrayList<String>();  
for(String lang:array){  
list.add(lang);  
}  
System.out.println("Printing List: "+list);  
  
}  
}  
Output:
Printing Array: [Java, Python, PHP, C++]
Printing List: [Java, Python, PHP, C++]
Question: How to convert List to Array?

Answer: We can convert the List to Array by calling the list.toArray() method. Let's see a simple example to convert list elements into array.

import java.util.*;  
public class ListToArrayExample{  
public static void main(String args[]){  
 List<String> fruitList = new ArrayList<>();    
 fruitList.add("Mango");    
 fruitList.add("Banana");    
 fruitList.add("Apple");    
 fruitList.add("Strawberry");    
 //Converting ArrayList to Array  
 String[] array = fruitList.toArray(new String[fruitList.size()]);    
 System.out.println("Printing Array: "+Arrays.toString(array));  
 System.out.println("Printing List: "+fruitList);  
}  
}  
Output:
Printing Array: [Mango, Banana, Apple, Strawberry]
Printing List: [Mango, Banana, Apple, Strawberry]
Question: What is Get and Set Element in List?

Answer: The get() method returns the element at the given index, whereas the set() method changes or replaces the element.

import java.util.*;  
public class ListExample2{  
 public static void main(String args[]){  
 //Creating a List  
 List<String> list=new ArrayList<String>();  
 //Adding elements in the List  
 list.add("Mango");  
 list.add("Apple");  
 list.add("Banana");  
 list.add("Grapes");  
 //accessing the element    
 System.out.println("Returning element: "+list.get(1));//it will return the 2nd element, because index starts from 0  
 //changing the element  
 list.set(1,"Dates");  
 //Iterating the List element using for-each loop  
 for(String fruit:list)  
  System.out.println(fruit);  
  
 }  
}  

Output:
Returning element: Apple
Mango
Dates
Banana
Grapes
Question: How to Sort List?

Answer: There are various ways to sort the List, here we are going to use Collections.sort() method to sort the list element. The java.util package provides a utility class Collections which has the static method sort(). Using the Collections.sort() method, we can easily sort any List.

import java.util.*;  
class SortArrayList{  
 public static void main(String args[]){  
  //Creating a list of fruits  
  List<String> list1=new ArrayList<String>();  
  list1.add("Mango");  
  list1.add("Apple");  
  list1.add("Banana");  
  list1.add("Grapes");  
  //Sorting the list  
  Collections.sort(list1);  
   //Traversing list through the for-each loop  
  for(String fruit:list1)  
    System.out.println(fruit);  
      
 System.out.println("Sorting numbers...");  
  //Creating a list of numbers  
  List<Integer> list2=new ArrayList<Integer>();  
  list2.add(21);  
  list2.add(11);  
  list2.add(51);  
  list2.add(1);  
  //Sorting the list  
  Collections.sort(list2);  
   //Traversing list through the for-each loop  
  for(Integer number:list2)  
    System.out.println(number);  
 }  
   
}
  
Output:
Apple
Banana
Grapes
Mango
Sorting numbers...
1
11
21
51
Question: What is Java ListIterator Interface?

Answer: ListIterator Interface is used to traverse the element in a backward and forward direction.
Question: What is the class declaration for Listlterator Interface?

Answer: public interface ListIterator<E> extends Iterator<E>