QA Interview: Top 30: Java Programs for QA Automation Interview

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1. How to reverse a string in java?

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

        System.out.print("Reverse is:");
        for(int i=n-1;i>=0;i--){
            System.out.print(str.charAt(i));
        }
     }
}

Output:
Enter a String: ABCD
Reverse is: DCBA
2.1 How to reverse a number in Java? (Convert int to string)

import java.util.Scanner;
public class Test{
     public static void main(String []args){
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a Number:");
        int num = sc.nextInt();
        String str = Integer.toString(num);
        int n = str.length();
        
        System.out.print("Reverse is:");
        for(int i=n-1;i>=0;i--){
            System.out.print(str.charAt(i));
        }
     }
}

Output:
Enter a Number:12345
Reverse is:54321
2.2 How to reverse a number in Java? (using % operator)

import java.util.Scanner;
public class Test{
     public static void main(String []args){
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a Number:");
        int original = sc.nextInt();
        int reverse = 0;
        
        while(original!=0){
              int rem = original % 10;
              reverse = reverse * 10 + rem;
              original = original /10;
        }
        System.out.println("Reverse Number:"+reverse);
     }
}

Output:
Enter a Number:123456
Reverse is:654321
3.1 Check if string is Palindrome or not (Using equals method)

import java.util.*;
class Test {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a String:");
        String original = sc.nextLine();
        int n = original.length();
        String reverse= "";
        
        for(int i=n-1;i>=0;i--){
            reverse=reverse+original.charAt(i);
        }
        
        if(original.equals(reverse)){
            System.out.println("String is palindrome");
        }else{
            System.out.println("String is not palindrome");
        }
    }
}

Output:
Enter a String: abcba
String is palindrome
3.2 Check if string is Palindrome or not

import java.util.Scanner;
class Test {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a String:");
        String original = sc.nextLine();
        int length = original.length();
        boolean isPalindrome = true;
        
        for(int i=0;i<length;i++){
            if(original.charAt(i)!=original.charAt(length-i-1)){
                System.out.println("String is not palindrome");
                isPalindrome = false;
                break;
            }
        }
        if(isPalindrome){
            System.out.println("String is palindrome");
        }
    }
}

Output:
Enter a String:abcba
String is palindrome
4.1 Swap two numbers without using third variable

import java.util.Scanner;
class Test {
    public static void main(String[] args) {
        int x=5,y=10;
        x=x+y;
        y=x-y;
        x=x-y;
        System.out.print("Values After Swapping = X:"+x+" Y:"+y);
    }
}

Output:
Values After Swapping = X:10 Y:5
4.2 Swap two numbers using third variable

import java.util.Scanner;
class Test {
    public static void main(String[] args) {
        int x=5,y=10;
        int temp=x;
        x=y;
        y=temp;
        System.out.print("Values After Swapping = X:"+x+" Y:"+y);
    }
}

Output:
Values After Swapping = X:10 Y:5 
5.1 Fibonacci Series (Starting from 0)

import java.util.Scanner;
class Test {
    public static void main(String[] args) {
        int a=0,b=1,c;
        for(int i=1;i<=10;i++){
            System.out.print(a+" ");
            c=a+b;
            a=b;
            b=c;
        }
    }
}

Output: 0 1 1 2 3 5 8 13 21 34
5.2 Fibonacci Series (Starting from 1)

import java.util.Scanner;
class Test {
    public static void main(String[] args) {
        int a=0,b=1,c;
        for(int i=1;i<=10;i++){
            c=a+b;
            a=b;
            b=c;
            System.out.print(a+" ");
        }
    }
}

Output: 1 1 2 3 5 8 13 21 34
6. Factorial of a Number

import java.util.Scanner;
class Test {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int fact=1;
        
        System.out.print("Enter a Number:");
        int num = sc.nextInt();
    
        for(int i=1;i<=num;i++){
            fact = fact*i;
        }
        System.out.print("Factorial of a Number:"+fact);
    }
}

Output:
Enter a Number:5
Factorial of a Number:120
7. Check if given number is prime number or not

import java.util.Scanner;
class Test {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a Number:");
        int num = sc.nextInt();
        int m=num/2;
        int flag=0;
        
        if(num==0 || num==1){
            System.out.print("Given number is not a prime number.");
            flag=1;
        }else{
            for(int i=2;i<=m;i++){
                if(num%i == 0){
                    System.out.print("Given number is not a prime number.");
                    flag=1;
                    break;
                }
            }
        }
        if(flag == 0){
            System.out.print("Given number is a prime number.");
        }
    }
}

Output:
Enter a Number:23
Given number is a prime number.
8. Program to display the prime numbers from 1 to 100

public class Test
{   
public static void main(String[] args) {
int a=1,b=100;
for(int i=a;i<=b;i++){
    if(checkPrime(i)){
        System.out.print(i+" " );
    }
}
}
public static boolean checkPrime(int num){
    // 0, 1 and negative numbers are not prime
    if(num<2){
        return false;
    }
    else{
// no need to run loop till num-1 as for any number x the numbers in
    // the range(num/2 + 1, num) won't be divisible anyways. 
    // Example 36 wont be divisible by anything b/w 19-35
        int x= num/2;
        for(int i=2;i<x;i++){
            if(num%i==0){
                return false;
            }
        }
    }
    // the number would be prime if we reach here
    return true;
}
}

Output:
2 3 4 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 
9.1 Count Occurrence of each character in a String

import java.util.*;
class Test {
    public static void main(String[] args) {
        String str = "iamiball";
        char arr[] = str.toCharArray();
        
        HashMap<Character,Integer> hm = new HashMap<Character,Integer>();
        
        for(char c:arr){
            if(hm.containsKey(c)){
                hm.put(c,hm.get(c)+1);
            }else{
                hm.put(c,1);
            }
        }
        
        for(Map.Entry <Character,Integer>e:hm.entrySet()){
            System.out.println(e.getKey()+" : "+e.getValue());
        }
    }
}

Output:
a : 2
b : 1
i : 2
l : 2
m : 1
9.2 Count Occurrence of each character in a String

import java.util.Scanner;
public class EachCharacterCount {
    public static void main(String args[]) {
        String str;
        int i, len, counter[] = new int[256];
 
        Scanner scanner = new Scanner(System.in);
        System.out.println("Please enter a string : ");
        str = scanner.nextLine();
        len = str.length();
 
        // loop through string and count frequency of every char and store it in counter array
        for (i = 0; i < len; i++) {
            counter[(int) str.charAt(i)]++;
        }
        
        // Print Frequency of characters
        for (i = 0; i < 256; i++) {
            if (counter[i] != 0) {
                System.out.println((char) i + " --> " + counter[i]);
            }
        }
    }
}

Output:
Please enter a string : 
iamiball
a --> 2
b --> 1
i --> 2
l --> 2
m --> 1
10. Count Occurrence of each word in a String

import java.util.*;
class Test {
    public static void main(String[] args) {
        String str = "India is my country. India is very beautiul";
        String arr[] = str.split(" ");
        
        HashMap<String,Integer> hm = new HashMap<String,Integer>();
        for(String s:arr){
            if(hm.containsKey(s)){
                hm.put(s,hm.get(s)+1);
            }else{
                hm.put(s,1);
            }
        }
        
        for(Map.Entry <String,Integer>e:hm.entrySet()){
            System.out.println(e.getKey()+" : "+e.getValue());
        }
    }
}

Output:
very : 1
beautiul : 1
is : 2
country. : 1
my : 1
India : 2

11. Write program for:
Input: 1,3,5,7,9,3,5,11,13,9 | Output: 1 3 5 7 9 11 13

import java.util.*;
class Test {
    public static void main(String[] args) {
        int[] arr={1,3,5,7,9,3,5,11,13,9};
        List<Integer> ls = new ArrayList<Integer>(arr.length);
        
        for(int i:arr){
            ls.add(i);
        }
        
        LinkedHashSet lhs = new LinkedHashSet(ls);
        Object[] obj = lhs.toArray();
        
        System.out.println("Printing numbers only once:");
        for(Object o:obj){
            System.out.print(o+ " ");
        }
    }
}

Output:
Printing numbers only once:
1 3 5 7 9 11 13
12. Remove duplicates from an integer array
Input: 1,3,5,7,9,11,13,3,5,7,15 | Output: 1 9 11 13 15 

import java.util.*;
class Test {
    public static void main(String[] args) {
        int[] arr = {1,3,5,7,9,11,13,3,5,7,15};
        HashMap<Integer,Integer> hm = new HashMap<Integer,Integer>();
        
        for(int i:arr){
            if(hm.containsKey(i)){
                hm.put(i,hm.get(i)+1);
            }else{
                hm.put(i,1);
            }
        }
        
        for(Map.Entry <Integer,Integer>e:hm.entrySet()){
            if(e.getValue() < 2){
            System.out.print(e.getKey()+" ");
        }
        }
    }
}

Output:
1 9 11 13 15 
13. Write program for:
Input: IND SL PAK SL NEP BAN SL | Output: IND, SL, PAK, NEP, BAN

import java.util.*;
class Test {
    public static void main(String[] args) {
        String arr[] = {"IND","SL","PAK","SL","NEP","BAN","SL"};
        ArrayList<String> al = new ArrayList<String>(arr.length);
        
        for(String s:arr){
            al.add(s);
        }
        
        LinkedHashSet<String> lhs = new LinkedHashSet<String>(al);
        Object[] obj = lhs.toArray();
        for(Object o:obj){
            System.out.print(o+" ");
        }
    }
}

Output:
IND SL PAK NEP BAN

14.  Remove duplicates from string array
Input: IND SL PAK SL NEP PAK BAN | Output: NEP IND BAN

import java.util.*;
class Test {
    public static void main(String[] args) {
        String[] arr = {"IND","SL","PAK","SL","NEP","PAK","BAN"};
        HashMap<String,Integer> hm = new HashMap<String,Integer>();
        
        for(String s:arr){
            if(hm.containsKey(s)){
                hm.put(s,hm.get(s)+1);
            }else{
                hm.put(s,1);
            }
        }
        
        for(Map.Entry <String,Integer>e:hm.entrySet()){
            if(e.getValue() < 2){
            System.out.print(e.getKey()+" ");
        }
        }
    }
}

Output:
NEP IND BAN 

15. Reverse words in a string array
Input: IND SL PAK NEP BAN | Output: BAN NEP PAK SL IND

import java.util.*;
class Test {
    public static void main(String[] args) {
        String[] arr = {"IND","SL","PAK","NEP","BAN"};
        ArrayList<String> al = new ArrayList<String>(arr.length);
        for(String s:arr){
            al.add(s);
        }
        Collections.reverse(al);
        Object[] obj = al.toArray();
        for(Object o:obj){
            System.out.print(o+" ");
        }
    }
}

Output: BAN NEP PAK SL IND

          

Next: Java Programs for QA Automation Interview (16-30)

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