hereral/Clara-Training-Data huggingface dataset:
Question: Can you provide an example of Java Comparator (Non-generic Old Style)?

Answer: Let's see the example of sorting the elements of List on the basis of age and name. In this example, we have created 4 java classes:

1.Student.java
2..AgeComparator.java
3.NameComparator.java
4.Simple.java

Student.java
This class contains three fields rollno, name and age and a parameterized constructor.

class Student{  
int rollno;  
String name;  
int age;  
Student(int rollno,String name,int age){  
this.rollno=rollno;  
this.name=name;  
this.age=age;  
}  
}  

AgeComparator.java
This class defines comparison logic based on the age. If the age of the first object is greater than the second, we are returning a positive value. It can be anyone such as 1, 2, 10. If the age of the first object is less than the second object, we are returning a negative value, it can be any negative value, and if the age of both objects is equal, we are returning 0.

import java.util.*;  
class AgeComparator implements Comparator{  
public int compare(Object o1,Object o2){  
Student s1=(Student)o1;  
Student s2=(Student)o2;  
  
if(s1.age==s2.age)  
return 0;  
else if(s1.age>s2.age)  
return 1;  
else  
return -1;  
}  
}  

NameComparator.java
This class provides comparison logic based on the name. In such case, we are using the compareTo() method of String class, which internally provides the comparison logic.

import java.util.*;  
class NameComparator implements Comparator{  
public int compare(Object o1,Object o2){  
Student s1=(Student)o1;  
Student s2=(Student)o2;  
  
return s1.name.compareTo(s2.name);  
}  
}  

Simple.java
In this class, we are printing the values of the object by sorting on the basis of name and age.
import java.util.*;  
import java.io.*;  
  
class Simple{  
public static void main(String args[]){  
  
ArrayList al=new ArrayList();  
al.add(new Student(101,"Vijay",23));  
al.add(new Student(106,"Ajay",27));  
al.add(new Student(105,"Jai",21));  
  
System.out.println("Sorting by Name");  
  
Collections.sort(al,new NameComparator());  
Iterator itr=al.iterator();  
while(itr.hasNext()){  
Student st=(Student)itr.next();  
System.out.println(st.rollno+" "+st.name+" "+st.age);  
}  
  
System.out.println("Sorting by age");  
  
Collections.sort(al,new AgeComparator());  
Iterator itr2=al.iterator();  
while(itr2.hasNext()){  
Student st=(Student)itr2.next();  
System.out.println(st.rollno+" "+st.name+" "+st.age);  
}  
  
  
}  
}  

      Sorting by Name
       106 Ajay 27
       105 Jai 21
       101 Vijay 23
       
       Sorting by age       
       105 Jai 21
       101 Vijay 23
       106 Ajay 27
Question: Can you provide an example of Java Comparator (Generic)?

Answer: 

Student.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;  
}  
} 
 
AgeComparator.java

import java.util.*;  
class AgeComparator implements Comparator<Student>{  
public int compare(Student s1,Student s2){  
if(s1.age==s2.age)  
return 0;  
else if(s1.age>s2.age)  
return 1;  
else  
return -1;  
}  
}  


NameComparator.java

This class provides comparison logic based on the name. In such case, we are using the compareTo() method of String class, which internally provides the comparison logic.

import java.util.*;  
class NameComparator implements Comparator<Student>{  
public int compare(Student s1,Student s2){  
return s1.name.compareTo(s2.name);  
}  
}  

Simple.java
In this class, we are printing the values of the object by sorting on the basis of name and age.

import java.util.*;  
import java.io.*;  
class Simple{  
public static void main(String args[]){  
  
ArrayList<Student> al=new ArrayList<Student>();  
al.add(new Student(101,"Vijay",23));  
al.add(new Student(106,"Ajay",27));  
al.add(new Student(105,"Jai",21));  
  
System.out.println("Sorting by Name");  
  
Collections.sort(al,new NameComparator());  
for(Student st: al){  
System.out.println(st.rollno+" "+st.name+" "+st.age);  
}  
  
System.out.println("Sorting by age");  
  
Collections.sort(al,new AgeComparator());  
for(Student st: al){  
System.out.println(st.rollno+" "+st.name+" "+st.age);  
}  
}  
}  
      Sorting by Name
       106 Ajay 27
       105 Jai 21
       101 Vijay 23

       Sorting by age     
       105 Jai 21
       101 Vijay 23
       106 Ajay 27
Question: What is Properties class in Java?
Answer: The properties object contains key and value pair both as a string. The java.util.Properties class is the subclass of Hashtable.

It can be used to get property value based on the property key. The Properties class provides methods to get data from the properties file and store data into the properties file. Moreover, it can be used to get the properties of a system
Question: What is the  Advantage of the properties file?

Answer: Recompilation is not required if the information is changed from a properties file: If any information is changed from the properties file, you don't need to recompile the java class. It is used to store information which is to be changed frequently.
Question: What are the Constructors of the Properties class?

Answer: Constructor:Properties()
Description: It creates an empty property list with no default values.

Constructor:Properties(Properties defaults)
Description:It creates an empty property list with the specified defaults.
Question: What are the Methods of Properties class?

Answer: Method:   public void load(Reader r)
Description: It loads data from the Reader object.

Method:   public void load(InputStream is)
Description: It loads data from the InputStream object

Method:   public void loadFromXML(InputStream in)
Description: It is used to load all of the properties represented by the XML document on the specified input stream into this properties table.

Method:  public String getProperty(String key) 
Description: It returns value based on the key.

Method:public String getProperty(String key, String defaultValue)   
Description: It searches for the property with the specified key.

Method:public void setProperty(String key, String value)   
Description: It calls the put method of Hashtable.

Method:   public void list(PrintStream out)
Description: It is used to print the property list out to the specified output stream.

Method:   public void list(PrintWriter out))
Description: It is used to print the property list out to the specified output stream.

Method: public Enumeration<?> propertyNames())  
Description: It returns an enumeration of all the keys from the property list.

Method:   public Set<String> stringPropertyNames()
Description: It returns a set of keys in from property list where the key and its corresponding value are strings.

Method:public void store(Writer w, String comment)   
Description: It writes the properties in the writer object.

Method:   public void store(OutputStream os, String comment)
Description: It writes the properties in the OutputStream object.

Method:   public void storeToXML(OutputStream os, String comment)
Description: It writes the properties in the writer object for generating XML document.

Method:   public void storeToXML(Writer w, String comment, String encoding)
Description: It writes the properties in the writer object for generating XML document with the specified encoding.
Question: Can you provide an example of Properties class to get information from the properties file?

Answer: To get information from the properties file, create the properties file first.

db.properties
user=system  
password=oracle  

Now, let's create the java class to read the data from the properties file.

Test.java

import java.util.*;  
import java.io.*;  
public class Test {  
public static void main(String[] args)throws Exception{  
    FileReader reader=new FileReader("db.properties");  
      
    Properties p=new Properties();  
    p.load(reader);  
      
    System.out.println(p.getProperty("user"));  
    System.out.println(p.getProperty("password"));  
}  
}  

Output:system
       oracle


Now if you change the value of the properties file, you don't need to recompile the java class. That means no maintenance problem.
Question: What are the Difference between ArrayList and Vector?

Answer: ArrayList and Vector both implements List interface and maintains insertion order.

However, there are many differences between ArrayList and Vector classes that are given  below.
1) ArrayList is not synchronized while Vector is synchronized.
2)  ArrayList increments 50% of current array size if the number of elements exceeds from its capacity while Vector increments 100% means doubles the array size if the total number of elements exceeds than its capacity.
3) ArrayList is not a legacy class. It is introduced in JDK 1.2 while Vector is a legacy class.
4)  ArrayList is fast because it is non-synchronized while Vector is slow because it is synchronized, i.e., in a multithreading environment, it holds the other threads in runnable or non-runnable state until current thread releases the lock of the object.
5) ArrayList uses the Iterator interface to traverse the elements while A Vector can use the Iterator interface or Enumeration interface to traverse the elements.
Question: What is Java Vector?

Answer: Vector is like the dynamic array which can grow or shrink its size. Unlike array, we can store n-number of elements in it as there is no size limit. It is a part of Java Collection framework since Java 1.2. It is found in the java.util package and implements the List interface, so we can use all the methods of List interface here.

It is recommended to use the Vector class in the thread-safe implementation only. If you don't need to use the thread-safe implementation, you should use the ArrayList, the ArrayList will perform better in such case.

The Iterators returned by the Vector class are fail-fast. In case of concurrent modification, it fails and throws the ConcurrentModificationException.

It is similar to the ArrayList, but with two differences-
-Vector is synchronized.
-Java Vector contains many legacy methods that are not the part of a collections framework.
Question: What is the class declaration for Java Vector class?

Answer: public class Vector<E>  
extends Object<E>  
implements List<E>, Cloneable, Serializable
Question: What are the Constructors of the Java Vector?

Answer: SN:1
Constructor: vector()
Description: It constructs an empty vector with the default size as 10.
 
SN:2
Constructor: vector(int initialCapacity)
Description: It constructs an empty vector with the specified initial capacity and with its capacity increment equal to zero.

SN:3
Constructor: vector(int initialCapacity, int capacityIncrement)
Description: It constructs an empty vector with the specified initial capacity and capacity increment.

SN:4
Constructor: Vector( Collection<? extends E> c)
Description: It constructs a vector that contains the elements of a collection c.
Question: Can you provide an example of Java Vector?

Answer: 

import java.util.*;  
public class VectorExample {  
       public static void main(String args[]) {  
          //Create a vector  
          Vector<String> vec = new Vector<String>();  
          //Adding elements using add() method of List  
          vec.add("Tiger");  
          vec.add("Lion");  
          vec.add("Dog");  
          vec.add("Elephant");  
          //Adding elements using addElement() method of Vector  
          vec.addElement("Rat");  
          vec.addElement("Cat");  
          vec.addElement("Deer");  
            
          System.out.println("Elements are: "+vec);  
       }  
}  


Output:
Elements are: [Tiger, Lion, Dog, Elephant, Rat, Cat, Deer]
Question: What is Java Stack Class?

Answer: In Java, Stack is a class that falls under the Collection framework that extends the Vector class. It also implements interfaces List, Collection, Iterable, Cloneable, Serializable. It represents the LIFO stack of objects. Before using the Stack class, we must import the java.util package. The stack class arranged in the Collections framework hierarchy.
Question: What are the Constructors of the Stack Class?

Answer: The Stack class contains only the default constructor that creates an empty stack.

public Stack()
Question: How to Creat a Stack?

Answer: If we want to create a stack, first, import the java.util package and create an object of the Stack class.

Stack stk = new Stack();  
Or
Stack<type> stk = new Stack<>();
Question: What are the Methods of the Stack Class?

Answer: 
We can perform push, pop, peek and search operation on the stack. The Java Stack class provides mainly five methods to perform these operations. Along with this, it also provides all the methods of the Java Vector class.

Method: empty()   
Modifier and Type: boolean
Description: The method checks the stack is empty or not.

Method:   push(E item)
Modifier and Type: E
Description: The method pushes (insert) an element onto the top of the stack.

Method:   pop()
Modifier and Type: : E
Description: The method removes an element from the top of the stack and returns the same element as the value of that function.

Method:   peek()
Modifier and Type: : E
Description: The method looks at the top element of the stack without removing it.

Method:   search(Object o)
Modifier and Type: int
Description: The method searches the specified object and returns the position of the object.
Question: What is Java Collection Interface?

Answer: Collection is a group of objects, which are known as elements. It is the root interface in the collection hierarchy. This interface is basically used to pass around the collections and manipulate them where the maximum generality is desired.
Question: What is Iterator in Java?

Answer: In Java, an Iterator is one of the Java cursors. Java Iterator is an interface that is practiced in order to iterate over a collection of Java object components entirety one by one. It is free to use in the Java programming language since the Java 1.2 Collection framework. It belongs to java.util package.

Though Java Iterator was introduced in Java 1.2, however, it is still not the oldest tool available to traverse through the elements of the Collection object. The oldest Iterator in the Java programming language is the Enumerator predated Iterator. Java Iterator interface succeeds the enumerator iterator that was practiced in the beginning to traverse over some accessible collections like the ArrayLists.

The Java Iterator is also known as the universal cursor of Java as it is appropriate for all the classes of the Collection framework. The Java Iterator also helps in the operations like READ and REMOVE. When we compare the Java Iterator interface with the enumeration iterator interface, we can say that the names of the methods available in Java Iterator are more precise and straightforward to use.
Question: What are the Advantages of Java Iterator?

Answer: 
Iterator in Java became very prevalent due to its numerous advantages. The advantages of Java Iterator are given as follows : 
-The user can apply these iterators to any of the classes of the Collection framework.
-In Java Iterator, we can use both of the read and remove operations.
-If a user is working with a for loop, they cannot modernize(add/remove) the Collection, whereas, if they use the Java Iterator, they can simply update the Collection.
-The Java Iterator is considered the Universal Cursor for the Collection API.
-The method names in the Java Iterator are very easy and are very simple to use.
Question: What are the Disadvantages of Java Iterator?
Answer: Despite the numerous advantages, the Java Iterator has various disadvantages also. The disadvantages of the Java Iterator are given below :

-The Java Iterator only preserves the iteration in the forward direction. In simple words, the Java Iterator is a uni-directional Iterator.
-The replacement and extension of a new component are not approved by the Java Iterator.
-In CRUD Operations, the Java Iterator does not hold the various operations like CREATE and UPDATE.
-In comparison with the Spliterator, Java Iterator does not support traversing elements in the parallel pattern which implies that Java Iterator supports only Sequential iteration.
-In comparison with the Spliterator, Java Iterator does not support more reliable execution to traverse the bulk volume of data.
Question: How to use Java Iterator?

Answer: When a user needs to use the Java Iterator, then it's compulsory for them to make an instance of the Iterator interface from the collection of objects they desire to traverse over. After that, the received Iterator maintains the trail of the components in the underlying collection to make sure that the user will traverse over each of the elements of the collection of objects.

If the user modifies the underlying collection while traversing over an Iterator leading to that collection, then the Iterator will typically acknowledge it and will throw an exception in the next time when the user will attempt to get the next component from the Iterator.
Question: What are the methods of Java Iterator?

Answer: The following figure perfectly displays the class diagram of the Java Iterator interface. It contains a total of four methods that are:

-hasNext()
-next()
-remove()
-forEachRemaining()

The forEachRemaining() method was added in the Java 8. Let's discuss each method in detail.

-boolean hasNext(): The method does not accept any parameter. It returns true if there are more elements left in the iteration. If there are no more elements left, then it will return false.
If there are no more elements left in the iteration, then there is no need to call the next() method. In simple words, we can say that the method is used to determine whether the next() method is to be called or not.

-E next(): It is similar to hasNext() method. It also does not accept any parameter. It returns E, i.e., the next element in the traversal. If the iteration or collection of objects has no more elements left to iterate, then it throws the NoSuchElementException.

-default void remove(): This method also does not require any parameters. There is no return type of this method. The main function of this method is to remove the last element returned by the iterator traversing through the underlying collection. The remove () method can be requested hardly once per the next () method call. If the iterator does not support the remove operation, then it throws the UnSupportedOperationException. It also throws the IllegalStateException if the next method is not yet called.

-default void forEachRemaining(Consumer action): It is the only method of Java Iterator that takes a parameter. It accepts action as a parameter. Action is nothing but that is to be performed. There is no return type of the method. This method performs the particularized operation on all of the left components of the collection until all the components are consumed or the action throws an exception. Exceptions thrown by action are delivered to the caller. If the action is null, then it throws a NullPointerException.
Question: Can you provide an example of Java Iterator?

Answer: Now it's time to execute a Java program to illustrate the advantage of the Java Iterator interface. The below code produces an ArrayList of city names. Then we initialize an iterator applying the iterator () method of the ArrayList. After that, the list is traversed to represent each element.

JavaIteratorExample.java

import java.io.*;  
import java.util.*;  
    
public class JavaIteratorExample {  
    public static void main(String[] args)  
    {  
        ArrayList<String> cityNames = new ArrayList<String>();  
    
        cityNames.add("Delhi");  
        cityNames.add("Mumbai");  
        cityNames.add("Kolkata");  
        cityNames.add("Chandigarh");  
        cityNames.add("Noida");  
    
        // Iterator to iterate the cityNames  
        Iterator iterator = cityNames.iterator();  
    
        System.out.println("CityNames elements : ");  
    
        while (iterator.hasNext())  
            System.out.print(iterator.next() + " ");  
    
        System.out.println();  
    }  
}  

Output:
CityNames elements: 
Delhi Mumbai Kolkata Chandigarh Noida
Question: What is Java Deque?

Answer: A deque is a linear collection that supports insertion and deletion of elements from both the ends. The name 'deque' is an abbreviation for double-ended queue.

There are no fixed limits on the deque for the number of elements they may contain. However, this interface supports capacity restricted deques as well as the deques with no fixed size limits. There are various methods which are provided to insert, remove and examine the elements.

These methods typically exist in two forms: the one that throws an exception when the particular operation fails and the other returns a special value which can be either null or false depending upon the operations.
Question: What is Java ConcurrentHashMap class?
Answer: A hash table supporting full concurrency of retrievals and high expected concurrency for updates. This class obeys the same functional specification as Hashtable and includes versions of methods corresponding to each method of Hashtable. However, even though all operations are thread-safe, retrieval operations do not entail locking, and there is not any support for locking the entire table in a way that prevents all access. This class is fully interoperable with Hashtable in programs that rely on its thread safety but not on its synchronization details..
Question: What is the class declaration for Java ConcurrentHashMap class?

Answer: public class ConcurrentHashMap<K,V>  
extends AbstractMap<K,V>  
implements ConcurrentMap<K,V>, Serializable
Question: Can you provide an example of Java ConcurrentHashMap class: computeIfAbsent()?

Answer: //import statement  
  
import java.util.concurrent.*;   
    
 import java.util.*;   
    
public class ConcurrentHashMapcomputeIfAbsentExample1_1 {   
    
    public static void main(String[] args)   
    {   
          // crete a HashMap and add some values   
        HashMap<String, Integer> mapcon   
            = new HashMap<>();   
        mapcon.put("k1", 100);   
        mapcon.put("k2", 200);   
        mapcon.put("k3", 300);   
        mapcon.put("k4", 400);   
        System.out.println("HashMap values :\n " + mapcon.toString());    
        mapcon.computeIfAbsent("k5", k -> 200 + 300);   
        mapcon.computeIfAbsent("k6", k -> 60 * 10);   
        System.out.println("New HashMap after computeIfAbsent :\n "+ mapcon);   
    }   
}
Output:
HashMap values :
 {k1=100, k2=200, k3=300, k4=400}
New HashMap after computeIfAbsent :
 {k1=100, k2=200, k3=300, k4=400, k5=500, k6=600}
Question: What is Java ConcurrentLinkedQueue Class?

Answer: ConcurrentLinkedQueue is an unbounded thread-safe queue which arranges the element in FIFO. New elements are added at the tail of this queue and the elements are added from the head of this queue.
Question: What are the class methods of Java ConcurrentLinkedQueue?
Answer: 
Method: add()
Description: Inserts the specified element at the tail of this queue

Method: addAll()
Description: Inserts all the elements which are present in the specified collection to the tail of this queue

Method: contains()
Description: Returns true if this queue contains the specified element

Method: forEach()
Description: Performs the given action for each element until all elements have been processed.

Method: isEmpty()
Description: Returns true if this queue contains no elements.

Method: iterator()
Description: Returns an iterator over the elements in this queue

Method: offer()
Description: Inserts the specified element at the tail of this queue

Method: remove()
Description: Removes the specified element from this queue, if this element is present in the queue

Method: removeAll()
Description: Removes all the elements of this in queue which are present in the specified collection.

Method: removeIf()
Description: Removes all the elements in this queue that satisfy the given predicate filter.

Method: retainAll()
Description: Retain only those elements in this queue that are present in the specified collection.

Method: size()
Description: Returns the number of the elements in this queue.

Method: spliterator()
Description: Returns a spliterator over the elements in this queue.

Method: toArray()
Description: Returns an array containing all the elements of this queue which are in proper sequence.