String important interview questions in java (2023)

1. Write a program to find duplicate characters in java(using Mapping).

import java.util.*;

class Duplicate

{

public static void main(String[] args)

{

System.out.println("Dulicate char in java::");

findDuplicates("java");

System.out.println("Dulicate char is Programming::");

findDuplicates("programming");

}

public static void findDuplicates(String str)

{

HashMap<Character,Integer> m=new HashMap<>();

char[] ch=str.toCharArray();

for(char c1:ch)

{

if(m.containsKey(c1))

{

m.put(c1,m.get(c1)+1);

}

else

{

m.put(c1,1);

}

}

Iterator<Character> itr=m.keySet().iterator();

while(itr.hasNext())

{

char ch1=itr.next();

if(m.get(ch1)>1)

{

System.out.println(ch1+": " + m.get(ch1));

}

}

}

}

Output:

Duplicate char in java:a: 2
Duplicate char in Programming:r:2 g:2 m:2

2.Write a program to find duplicate words in java.

import java.util.*;

class Test

{

public static void main(String[] args)

{

findDuplicatesWords("My java java oh my java oh my java");

}

public static void findDuplicatesWords(String s)

{

String[] str=s.split(" ");

HashMap<String,Integer> m=new HashMap<>();

for(String s1:str)

{

if(m.get(s1)!=null)

{

m.put(s1,m.get(s1)+1);

}

else

{

m.put(s1,1);

}

}

Iterator<String> itr=m.keySet().iterator();

while(itr.hasNext())

{

String temp=itr.next();

if(m.get(temp)>1)

{

System.out.println(temp+"::"+m.get(temp));

}

}

}

}

Output:

java::4

oh::2

my::2

3.Write a program to reverse a given string in java in java .

import java.util.Scanner;
class Test
{
static String revStr="";
static String origStr;
public static void main(String[] args)
{

reverseString();



}

public static void reverseString()
{
System.out.println("Enter a string for reverse");
Scanner sc=new Scanner(System.in);
origStr=sc.nextLine();
int len=origStr.length();
for(int i=len-1;i>=0;i--)
{
revStr=revStr+origStr.charAt(i);
}

System.out.println("orignal string is: "+ origStr);
System.out.println("reverseString  string is: "+ revStr);

}

}

OUTPUT:
java
orignal string is: java
reverseString  string is: avaj

4. Write a program to check whether string is palindrome or not in java .

import java.util.Scanner;

class Test

{

public static void main(String[] args)

{

String revStr="";

String origStr;

System.out.println("Enter a string for reverse");

Scanner sc=new Scanner(System.in);

origStr=sc.nextLine();

int len=origStr.length();

for(int i=len-1;i>=0;i--)

{

revStr=revStr+origStr.charAt(i);

}

if(origStr.equals(revStr))

{

System.out.println("String is palindrome!!");

}

else

{

System.out.println("String is not a palindrome!!");

}

}

}

OUTPUT:

Enter a string for reverse

java

String is not a palindrome!!

5.Write a program to count total number of characters in the given String  in java By input to user.

import java.util.Scanner;
class Test
{
public static void main(String[] args)
{
String str;
System.out.println("Enter a string:");
Scanner sc=new Scanner(System.in);
str=sc.nextLine();

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

}

System.out.println("No of characters in string are:"+count);
}
}

OUTPUT:
Enter a string:
viren
No of characters in string are:5