Top 20 Java Interview Programs

Below programs covered in section:

Fibonacci Series, Armstrong Number, Anagrams Number, Prime Number, Reverse Number / Palindrome Number, Perfect Number, Duplicate Numbers and String/ Word/Characters, Factorial of number,  String Rotation, Binary to Decimal, Largest & Second largest Number, Calculate Sum of All Numbers Contained in String, Find Number of Words in Paragraph, Programs on patterns Of Triangles, Print Pyramid, Number series etc.

1. Fibonacci Series:

public static void main(String[] args) throws Exception {

int ipnum=6, oldVal=1, newVal=1, sum=0;

for(int i=0; i<=ipnum; i++)

{

System.out.print(" "+sum);//0 1 1 2 3 5 8

oldVal=newVal;

newVal=sum;

sum=oldVal + newVal;

}

}

Output:
0 1 1 2 3 5 8

2. Armstrong Number:

int num, rem, sum=0, temp;

System.out.println("Enter any number:");

Scanner sc =new Scanner(System.in);

num=sc.nextInt();

temp=num;

while (num!=0) {

rem = num % 10;

sum = sum+rem*rem*rem; 

num= num /10;

}

if(sum==temp)

{

System.out.println("Armstrong Number");

}

else

System.err.println("Not Armstrong Number");

}
}

Output:
Enter any number:
153
Armstrong Number

3. Anagrams Number:

public static void main(String[] args) {

System.out.println("Enter String: ");

Scanner sc=new Scanner(System.in);

String str1=sc.nextLine();

System.out.println("Enter Another String: ");

String str2=sc.nextLine();

//Step 1: Convert to Char Array

char [] c1=str1.toCharArray();

char [] c2=str2.toCharArray();

//Step 2: Sort an Array

Arrays.sort(c1);

Arrays.sort(c2);

//Step 3:Compare by equals()

if (Arrays.equals(c1, c2)) {

System.out.println("****Anagrams****");}

else {

System.err.println("**Not Anagrams**");

}

}

Output:
Enter String: Tony
Enter Another String: Stark
**Not Anagrams**

(Check for Anagrams)
Enter String: Fired
Enter Another String: Fried
****Anagrams****

4. Duplicate Numbers:

public static void main(String a[]) {

int[ ] numbers = { 21, 12, 35, 31, 24, 73, 64, 85, 55, 35, 24};

Arrays.sort(numbers);

for(int i = 1; i < numbers.length; i++) {

if(numbers[i] == numbers[i-1])

{

System.out.println("Duplicate: " + numbers[i]);

} }

Output:
Duplicate numbers are:  24 35

5. Find Duplicate String/ Word:

String str="Tutorials core Java and advanced Java and Java programming";

List<String> list=Arrays.asList(str.split(" ")); //Split all spaces 

Set<String> set=new HashSet<String>(list); 

for(String s : set)

{

System.out.println(s+" "+Collections.frequency(list, s));

}

Output:
core 1
Java 3
advanced 1
and 2
Tutorials 1
programming 1

5. Find Duplicate Characters:

public static void main(String[] args) {

String str="pursuit of happiness";

Map<Character, Integer> hm = new HashMap<Character, Integer>();

char[] chrs = str.toCharArray();

for(Character ch: chrs){

if(hm.containsKey(ch)){

hm.put(ch, hm.get(ch)+1);

}

else {

hm.put(ch, 1);

}

}

Set<Character> keys = hm.keySet();

for(Character ch:keys){

if(hm.get(ch) > 1)

{

System.out.println(ch+"--->"+hm.get(ch));

}

}

Output:
  --->2  //space
i--->2
p--->3
s--->3
u--->2

6. Find Number of Words in Paragraph:

public static void main(String[] args) {

System.out.println("Enter the string: ");

Scanner sc = new Scanner(System.in);

String str=sc.nextLine();

String[] words = str.trim().split(" ");

System.out.println("Number of words= "+words.length);

}

Output:
Enter the string:
The Lord of the King: The Return of the Ring
Number of words= 10



7. Reverse Number / Palindrome Number:

int num, temp, sum=0, rem; 
System.out.println("Enter any number:");
Scanner sc =new Scanner(System.in);
num=sc.nextInt();
temp=num; //store temp value of num to temp variable


while (num>0)

{

rem= num % 10; //3 //2 //1

sum=sum*10 + rem; //3 //32 //321

num= num / 10; //12 //1 //0

}

System.out.println("Reverse Number is:"+sum);

if(sum == temp){

System.out.println("It's Palidrome Number...I");

}

else

System.err.println("Not Palidrome Number...");

}

Output:

Enter any number:
143
Reverse Number is:341
Not Palidrome Number...

Enter any number:
151
Reverse Number is:151
It's Palidrome Number!

8. String Rotation:

String s1 = "nullpointer";

String s2 = "pointernull";

String s3 = s1 + s1;

if(s3.contains(s2)) {

System.out.println("Rotation Version");

}

else{

System.err.println("Not rotation Version");

}

}

Output:
Rotation Version

9. Check Prime Number:

int num, temp, sum=0, rem, den=2; 
System.out.println("Enter any number:");
Scanner sc =new Scanner(System.in);
num=sc.nextInt();
temp=num; //store temp value of num to temp variable

while (den<num) {

if (num % den == 0) {

System.err.println("Not Prime Number");

break;

}

den++;

}

if (den==num) {

System.out.println("Prime Number!");

}

Output:
Enter any number:
47

Prime Number!

10. Find Largest & Second largest Number:

int large= 0;

int secondlarge= 0;
int array[]={1,6,3,140,799,24,55,77};

for(int i=0; i<array.length; i++)

{

//for large

if(array[i]>large)

{

secondlarge = large;

large= array[i];

}

//for secongLarge

else if(array[i] > secondlarge)

{

secondlarge = array[i];

}

}

System.out.println("Large:"+large);

System.out.print("Second Large:"+secondlarge);

}

Output:
Large:799

Second Large:140

11. Calculate Sum of All Numbers Contained in String:

public static void main(String[] args) {

String str="Marriage on 11th May at 10:45 am and reception on 12th May at 8:30pm";

//1. replace non digit as Space

str=str.replaceAll("[\\D]", " ");

//2. Split into Space

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

int sum=0;

for (int i = 0; i < splits.length; i++) {

try {

sum = sum + Integer.parseInt(splits[i]);

}

catch (Exception e) {

}

}

System.out.println(sum);

}

Output:
Sum of all numbers:116

12. Calculate Factorial / Sum of all numbers:

int num, temp, sum=0, fact=1; 
System.out.println("Enter any number:");
Scanner sc =new Scanner(System.in);
num=sc.nextInt();

for (int i = 1; i <= num; i++) {

fact = fact *i;

sum = sum + i;

}

System.out.println("Factorial is:"+fact);

System.out.println("Sum is:"+sum);

Output:
Enter any number: 5
Factorial is:120

Sum is:15

13. Perfect Number: (Please google about perfect number)

int num, temp, sum=0; 
System.out.println("Enter any number:");
Scanner sc =new Scanner(System.in);
num=sc.nextInt();

for (int i = 1; i <=num/2; i++) {

i
f (num%i==0) {

sum = sum+i;

}

}

if (sum==num) {

System.out.println("Perfect Number: "+num);

}

else{

System.err.println("Not a Perfect Number");

}

Output:
Enter any number: 28
Yeah..It's Perfect Number

14. Binary to Decimal:

int sum=0, rem, i=0;
int num=1111; //Or we can take number from console

while(num>0)

{

rem=num%10;

sum=(int) (sum + rem * Math.pow(2, i));

num=num/10;

i++;

}

System.out.println(sum); 

Output: 
15

15. Decimal to Binary:

int num=15, index =0;

int binary[]=new int[10];

while (num>0)

{

binary [index++]=num % 2;

num=num/2;

}

for (int i = index-1; i >=0; i--) {

System.out.print(binary[i]);

}

} 

Output: 

1111

16. Patterns Of Triangle and Others:

public class Patterns {

public static void main(String[] args) {

/** 1. Ascending Order

*

* for column: for rows:

* 1 2 3 4 5 1 1 1 1 1

1 2 3 4 5 2 2 2 2 2

1 2 3 4 5 3 3 3 3 3

1 2 3 4 5 4 4 4 4 4

1 2 3 4 5 5 5 5 5 5

*/

for (int i=1; i <=5; i++) {

    for (int j=1; j <=5; j++) {

       System.out.print(i+" ");

  }

      System.out.println(" ");

 }

/** 2. Descending Order

*

5 4 3 2 1 5 5 5 5 5

5 4 3 2 1 4 4 4 4 4

5 4 3 2 1 3 3 3 3 3

5 4 3 2 1 2 2 2 2 2

5 4 3 2 1 1 1 1 1 1

*/

for (int i=5; i>=1; i--)  {

     for (int j=5; j>=1; j--) {

         System.out.print(i+" ");

   }

         System.out.println(" ");

}

/**

* 3. Characters in Ascending Orders:

*

A A A A A A B C D E

B B B B B A B C D E

C C C C C A B C D E

D D D D D A B C D E

E E E E E A B C D E

*/

for (char i ='A'; i <='E'; i++) {

     for (char j ='A'; j <='E'; j++) {

         System.out.print(i+" ");

    }

       System.out.println(" ");

}

/**

* 4. Characters in Descending Orders:

*

E D C B A E E E E E

E D C B A D D D D D

E D C B A C C C C C

E D C B A B B B B B

E D C B A A A A A A

*/

for (char i ='E'; i >='A'; i--) {

      for (char j ='E'; j >='A'; j--) { 

        System.out.print(j+" ");

    }

        System.out.println(" ");

   }

/**

* 5. Triangle: (check condition in column loop)

*

* 1 1

* * 1 2 2 2

* * * 1 2 3 3 3 3

* * * * 1 2 3 4 4 4 4 4

* * * * * 1 2 3 4 5 5 5 5 5 5

Do same for Characters and reverse numbers:

*/

for (int i=1; i<=5; i++) {

      for (int j=1; j<=i; j++) {

        System.out.print(i+" ");

      } 

       System.out.println(" ");

   }

/**

*  6. Triangle as below:

5 5 5 5 5 1 2 3 4 5 * * * * *

4 4 4 4 1 2 3 4 * * * *

3 3 3 1 2 3 * * *

2 2 1 2 * *

1 1 *

*Do same for Characters:

*/

for (int i=5; i>=1; i--) {

for (int j=1; j<=i; j++) {

System.out.print(j+" ");

}

System.out.println(" ");

}

for (char i='A'; i<='E'; i++) {

for (int j='E'; j>=i ;j--) {

System.out.print(i+" ");

}

System.out.println(" ");

}}

}

17. Prog to Print Pyramid

*

***

*****

*******

int i, j, k;

int min = 1, num=4 (4 rows of *);

for (i = 0; i < num; i++) {

      for (j = num - 1; j > i; j--) {

          System.out.print(" "); //here should be a space

   }

     for (k = 0; k < min; k++) {

   System.out.print("*");

}

   System.out.println();

   min = min + 2;

}

18. Program to Print Rectangle:

 *****

*      *

*      *

*      *

 *****

int i,j;

for(i=0; i<=4; i++){

     for(j=0; j<=4; j++){

           if (i==4 ||i==0 || j==4|| j==0) {

             System.out.print("*");

         }

else{

System.out.print(" ");

     }

  }

System.out.println();
}

19. Program to Print Series Of Numbers:

1 2 3 4 5

2 3 4 5 1

3 4 5 1 2

4 5 1 2 3

5 1 2 3 4

int i,j;

for(i=1; i<=5; i++){

     for(j=1; j<=5; j++){

int k=i+j-1;

if (k>5) {

System.out.print(k-5+" ");

}

else{

System.out.print(k+" ");

     }

  }

System.out.println();

}

20. Prog to Swap numbers without using 3rd variable:

public static void main(String[] args) {
int x, y;
System.out.print("Enter x and y : ");
Scanner in = new Scanner(System.in);
x = in.nextInt();
y = in.nextInt();

System.out.println("Before Swapping: " + " x=" + x + " y=" + y);
x = x + y;
y = x - y;
x = x - y;
System.out.println("After Swapping: " + " x=" + x + " y=" + y);

}




Please Note: Another new advance programs will upload soon on all core Java topics.