What is JAVA !!!

1.    JAVA is a technology.

2.    Java is an OOP language.

3.    JAVA is a Platform.

Note : A Platform is hardware & software environment where we execute our java program. JAVA is itself a platform, bcz JAVA has it's own JRE(Java Runtime Environment).

How to convert ArrayList to String array in Java.

ArrayListExample1.java

package java8s;

import java.util.*;

public class ArrayListExample1 {

    public static void main(String[] args) {

        List al = new ArrayList<String>();

         

        al.add("First");

        al.add("Second");

        al.add("Third");

        al.add("Fourth");

        al.add("Fivth");

     

        String[] s1 = new String[al.size()];

        al.toArray(s1);

     

        for(String s2 : s1)

        System.out.println(s2);

    }

}

Output:

First

Second

Third

Fourth

Fivth

How to avoid duplicates from List / ArrayList

Hii frnds…this is the question that I have faced many times in interview, very popular frequently asked question. Let’s see in detail.

ArrayListExample.java

package java8s;

import java.util.*;

public class ArrayListExample {

          public static void main(String[] args) {

                  

                  

                                      ArrayList al = new ArrayList();

                    

                                            al.add("First");

                                            al.add("Second");

                                            al.add("Third");

                                            al.add("First");     //Duplicate

                                            al.add("First");     //Duplicate

                    

                                          

                                              ArrayList al1 = new ArrayList(new HashSet(al));     

                    

                                           // ArrayList al2 = new ArrayList(new LinkedHashSet(al));     

                    

                                           Iterator it= al1.iterator();

                                           while(it.hasNext())

                                           {

                                                 System.out.println(it.next());

                                           }

                    

                             }

                  

          }

Output:

Second

Third

First 

JAVA Program to check whether a given string is palindrome or not without taking the concept of reverse

.import java.util.*;
class StringPalindrome {

public static void main(String[] args)
{
String str;
int l,c=0;
Scanner s= new Scanner(System.in);
System.out.println("enter a string");
str= s.nextLine();
l=str.length();
for(int i=0;i<(l-1)/2; i++)
{
if(str.charAt(i)==str.charAt(l-1-i))
{
continue;
}
else
{
c++;
}
}
if(c==0)
System.out.println("the given string is a pallindrome");
else
System.out.println("the given string is a not pallindrome");

}

}

Output
enter a string
katak
the given string is pallindrome

Interface in JAVA 8(JDK 1.8 version)

It is possible to define method inside the interface by implementing default method or static method in JAVA 8.

Example1: using default method:

package test;

interface A{

default void show()

{

     System.out.println("java");

}

}

class B implements A

{

    

}

class InterfaceExample1

{

     public static void main(String[] args)

     {

          B obj=new B();

          obj.show();

     }

}

Output

java

Example2: Using static method:

package test;

interface A{

static void show()

{

    System.out.println("java");

}

}

class InterfaceExample2

{

    public static void main(String[] args)

    {

        A.show();

    }

}

Output

java

Why Interface in Java ?

Ans:

1. Support the functionality of multiple inheritance.

2. Achieve fully abstraction.

3. Achieve loose coupling, which is the biggest advantage of interface.

How to sort ArrayList in JAVA.

To sort values in ArrayList, we use Collections class, and invoke sort() method. consider this example:

package java8s;

 

import java.util.*;

 

public class SortCollectionDemo {

 

public static void main(String[] args)

{

 

    List li = new ArrayList();

 

    li.add("Santosh");

    li.add("Akshay");

    li.add("Tapuuu");

    li.add("Millan);

    li.add("Rakesh");

 

    Collections.sort(li);

 

for(String temp: li)

{

System.out.println("Countries : "+temp);

}

}

}

Output:

Akshay

Millan

Rakesh

Santosh

Tapuuu