Home Java Coding Questions LazyQA.com Frequently Asked Java Programs for QA Top 10 numbers Questions 1. Swap two numbers Input: a = 100, b= 200; Output: a = 200, b= 1 00; public static void main(String[] args ) { int a = 100, b = 200; System. out .println( "After swapping, a = " + a + " and b = " + b ); // 1. Swapping using three Variables int temp = a ; a = b ; b = temp ; System. out .println( "After swapping, a = " + a + " and b = " + b ); // 2. Using Two Variables a = a + b ; b = a - b ; a = a - b ; System. out .println( "After swapping, a = " + a + " and b = " + b ); // 3. Swapping a and b using XOR a = a ^ b ; b = a ^ b ; a = a ^ b ; System. out .println( "After swapping, a = " + a + " and b = " + b ); } ------------------------------------------------------------------------------------------------------------ 2. Ar mstrong number - Armstrong number is a number that is equal to the sum of cubes of its digits. Input: 153 , Output: Yes 153 is an Armstrong number. ==> (1*1*1) + (5*5*5) + (3*3*3) = 153 public static void main(String[] args ) { int sum = 0, res , temp ; int num = 153; // It is the number to check Armstrong temp = num ; while ( num > 0) { res = num % 10; num = num / 10; sum = sum + ( res * res * res ); } if ( temp == sum ) System. out .println( temp + " is armstrong number" ); else System. out .println( temp + " is Not arms trong number" ); } ------------------------------------------------------------------------------------------------------------ LazyQA.com 3. Fibonacci Series – In Fibonacci series, next number is the sum of previous two numbers Input = First 10 Numbers Output = 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55 etc. The first two numbers of Fibonacci series are 0 and 1. public static void main(String[] args ) { int num1 = 0, num2 = 1, num =10; for ( int i = 0; i <= num ; i ++) { System. out .print( num1 + " " ); int num3 = num2 + num1 ; // S wap num1 = num2 ; num2 = num3 ; } } ------------------------------------------------------------------------------------------------------------ 4. Reverse a numbers and Number is Palindrome or Not. Input = 12321 Output =12321 public static void main(String[ ] args ) { int num = 12321; // 1. Reverse a Number Using the While Loop reversed number int rev = 0; int temp = num ; int rem ; // remainder while ( num > 0) { rem = num % 10; rev = ( rev * 10) + rem ; num = num / 10; } System. out .println( "Reversed Number is " + rev ); // Verify number is palindrome or not if ( rev == temp ) { System. out .println( "palindrome number " ); } else { System. out .println( "not palindrome" ); } } -------------------------------------------------------------------------------------------------- ---------- 5. Factorial Number Factorial Program in Java: Factorial of n is the product of all positive descending integers. Input = 5! O utput = 5! = 5*4*3*2*1 = 120 LazyQA.com public static void main(String[] args ) { Scanne r sc = new Scanne r (System. in ); System. out .println( "Enter number which you want for Factorial: " ); int num = sc .nextInt(); int fact = 1; for ( int i = 1; i <= num ; i ++) { fact = fact * i ; } System. out .println( "Factorial of" + num + " is " + fact ); } ------------------------------------------------------------------------------------------------------------ 6. OddEvenNumbers I nput = 11 O utput = Given number is odd number public static void main(String[] args) { // 1. Using Brute Force w Approach Scanne r sc = new Scanne r (System.in); System.out.println( "Enter Number: - " ); int num = sc.nextInt(); if (num % 2 == 0) // Brute Force w Approach { System.out.println( "Given is even number" ); } else { System.out.println( " Given number is odd number" ); } ------------------------------------------------------------------------------------------------------------ 7. Prime Numbe r Prime number is a number that is greater than 1 and divided by 1 or itself only. Input = 31 , O utput = The number is prime . public static void main(String[] args ) { int num = 31; int count = 0; if ( num <= 1) { System. out .println( " The number is not prime" ); return ; } for ( int i = 2; i <= num / 2; i ++) { if ( num % i == 0) count ++; } if ( count > 1) { System. out .println( "The number is not prime" ); } else { System. out .println( "The number is prime" ); } ------------------------------------------------------------------------------------------------------------ LazyQA.com 8. Largest number from 3 number/ given list public static void main(String[] args) { // TODO Auto - generated method stub // 1. By using if else condition int num1 = 7, num2 = 9, num3 = 10; if( num1 >= num2 && num1 >= num3) System.out.println(num1 + " is the largest number."); else if (num2 >= num1 && num2 >= num3) System.out.println(num2 + " is the largest number."); else System.out.println(num3 + " is the largest number."); // 2. Using Collections.max() method and ArrayList ArrayList<Integer> x = new ArrayList<>(); x.add(12); x.add(22); x.add(54); System.out.println(Collections.max(x)+ " is the largest number."); } ------------------------------------------------------------------------------------------------------------ 9. Sum o f Digits Sum of all given numbers. Input = 987 Output = 24 public static void main(String[] a rgs ) { int n = 987; int sum = 0; while ( n != 0) { sum = sum + n % 10; n = n / 10; } System. out .println( "Using While: - " + sum ); } ------------------------------------------------------------------------------------------------------------ 10. Count digits in an integer number Input = 29845315 , Output = 8 public static void main(String[] args ) { // TODO Auto - generated method stub long num = 29845315; int count = 0, num2 = 298453; // 1. by using while loop while ( num != 0) { LazyQA.com num = num / 10; count ++; } System. out .println( "Number of digits : " + count ); // 2. Converting given number to string solution to count digits in an integer String result = Integer. toString ( num2 ); // calculate the size of string System. out .println(+ result .length()); } ------------------------------------------------------------------------------------------------------------ Top 15 String Que stions 1. Reverse a string Input = mama Output = mama public static void main(String[] args) { String str = "mama"; String s2 = ""; // 1. by using the charAt() method for (int i = str.length() - 1; i >= 0; i -- ) { s2 = s2 + str.charAt(i);// extracts each character and store in string } System.out.println("Reversed word: " + s2); // below is code to check weather given string is Palindrome or not if (str.equalsIgnoreCase( s2 )) { System. out .println("String is Palindrome"); } else { System. out .println("String is not Palindrome"); } } // 2 . Using built in reverse() method of the StringBuilder class: String input = "Welcome To Jave Learning"; StringBuilder input1 = new StringBuilder(); input1.append(input); // append a string into StringBuilder input1 input1.reverse(); System. out .println(inp ut1); // 3. Using StringBuffer: String strText = "Java Learning"; // conversion from String object to StringBuffer StringBuffer sbr = new StringBuffer(strText); sbr.reverse(); System. out .println(sbr); ------------------------------------------------------ ------------------------------------------------------ LazyQA.com 2. Remove space form given string Input String = “ hello java Learning ” Output String = “ hello java Learning ” public static void main(String[] args ) { System. out .println( "Enter String " ); Scanne r sc = new Scanne r (System. in ); String input = sc .nextLine(); System. out .println( "Original String - " + input ); input = input .replaceAll( " \ \ s" , "" ); System. out .println( "Final String - " + input ); } ------------------------------------------------------------------------------------------------------------ 3. Finding Common Elements in Array s Input = array1 = { 4, 2, 3, 1, 6 }; array2 = { 6, 7, 8, 4 }; Output = 6,4 // By using the for loop Integer[] array1 = { 4, 2, 3, 1, 6 }; Integer[] array2 = { 6, 7, 8, 4 }; List<Integer> commonElements = new ArrayList<>(); for ( int i = 0; i < array1 . length ; i ++) { for ( int j = 0; j < array2 . length ; j ++) { if ( array1 [ i ] == array 2 [ j ]) { commonElements .add( array1 [ i ]); } }} System. out .println( "Common Elements for given two array List is:" + commonElements ); // by using ArrayList with retainAll method ArrayList<Integer> list1 = new ArrayList<>(Arrays. asList ( array1 )); ArrayList<Integ er> list2 = new ArrayList<>(Arrays. asList ( array2 )); list1 .retainAll( list2 ); System. out .println( "Common Elements:" + list1 ); // By using Java Stream String[] array3 = { "Java" , "JavaScript" , "C" , "C++" }; String[] array4 = { "Python" , "C#" , "Java" , "C++" } ; ArrayList<String> list3 = new ArrayList<>(Arrays. asList ( array3 )); ArrayList<String> list4 = new ArrayList<>(Arrays. asList ( array4 )); List<String> commonElements1 = list3 .stream().filter( list4 ::contains).collect(Collectors. toList ()); System. out .println( com monElements1 ); } } ------------------------------------------------------------------------ ---------------------- LazyQA.com 4 . Find first and last element of ArrayList in java Input = array1 = { 4, 2, 3, 1, 6 }; Output = First is:4, Last is : 6 ArrayList<Integer> list = new ArrayList<Integer>(5); // find first element int first = list.get(0); //First Element // find last element int last = list.get(list.size() - 1); //last Element ------------------------------------------------------------------------ ---------------------- 5. Second Largest and Second Smallest Numbers: // Code to find secon d largest and second smallest numbers in an array int [] arrayList = { 4, 2, 3, 1,0, 6,12,15,20 }; int num = arrayList . length ; Arrays. sort ( arrayList ); System. out .println( "Second Largest element is " + arrayList [ num - 2]); //Display Second Smallest System. out .prin tln( "Second Smallest element is " + arrayList [1]); ------------------------------------------------------------------------- --------------------- 6 . How to sort an Array without using i nbuilt method? Input = array[] = { 10, 5, 20, 63, 12, 57, 88, 60 }; Output = 5 10 12 20 57 60 63 88 int temp, size; int array[] = { 10, 5, 20, 63, 12, 57, 88, 60 }; size = array.length; for (int i = 0; i < size; i++) { for (int j = i + 1; j < size; j++) { if (array[i] > array[j]) { temp = array[i]; array[i] = array[j]; array[j] = temp; }}} for (int i = 0; i < array.length; i++) { System.out.println(" Array sorted: " + array[i]); } // Print 3rd Largest number from an Array System.out.println("Third largest number is:: " + array[size - 3]); System.out.println("*********************"); // sort array using the Arrays.sort method Arrays.sort(array); System. out.println("sorted array - " + Arrays.toString(array)); int thirdMaxNum=array[size - 3]; System.out.println("Third highest array - " +thirdMaxNum ); ------------------------------------------------------------------------- --------------------- LazyQA.com 7 . Co unting number of occurrences of given word in a string using Java? String = "Java is a programming language. Java is widely used in software Testing" ; Input = ” J ava ” , Output = 2 public static void main(String[] args ) { String string = "Java is a programming language. Java is widely used in software Testing" ; String[] words = string .toLowerCase().split( " " ); String word = "java" ; int occurrences = 0; for ( int i = 0; i < words . length ; i ++) if ( words [ i ].equals( word )) occurrences ++; System. out .println( occurrences ); } ------------------------------------------------------------------------- --------------------- 8 . Find each word occurrence from given st ring in string java Input = "Alice is girl and Bob is boy"; Output = {Bob=1, Alice=1, and=1, is=2, girl=1, boy=1} public static void main(String[] args ) { String str = "Alice is girl and Bob is boy" ; Map<String, Integer> hashMap = new HashMap<>(); String[] words = str .split( " " ); for (String word : words ) { if ( hashMap .containsKey( word )) hashMap .put( word , hashMap .get( word ) + 1); else hashMap .put( word , 1); } System. out .println( hashMap ); ------------------------------------------------------------------------------------------------------------ 9 . Reverse the entire sentence Input = "India is country My" Output = "My country is India" public static void main(String[] args ) { String str [] = "India is country My" .split( " " ); String ans = "" ; for ( int i = str . length - 1; i >= 0; i -- ) { ans = ans + str [ i ] + " " ; } System. out .println( ans .substring(0, ans .length() - 1)); } LazyQA.com 10 . count the occurrences of each character? Input = "This is an example"; Output = p = 1, a = 2, s = 2, T = 1, e = 2, h = 1, x = 1, i = 2, l = 1, m = 1, n = 1 public static void main(String[] args ) { String str = "This is an example" ; Has hMap<Character, Integer> count = new HashMap<Character, Integer>(); // convert string to character array char [] arr = str .toCharArray(); // traverse every character and count the Occurrences for ( char c : arr ) { // filter out white spaces if ( c != ' ' ) { if ( count .containsKey( c )) { // if character already traversed, increment it count .put( c , count .get( c ) + 1); } else { // if character not traversed, add it to hashma p count .put( c , 1); } } } // traverse the map and print the number of occurence s of a charact er for ( Map.Entr y entry : count .entrySet()) { System. out .print( entry .getKey() + " = " + entry .getValue()+ ", " ); } } ------------------------------------------------------------------------- ------------------------------- 11 . Removing Duplicates from an Array // using for loop String[] strArray = { "abc" , "def" , "abc" , "mno" , "xyz" , "pqr" , "xyz" , "pqr" }; //1. Using Brute Force Method for ( int i = 0; i < strArray . length - 1; i ++) { for ( int j = i +1; j < strArray . length ; j ++) { if ( ( strArray [ i ]==( strArray [ j ])) ) { System. out .println( "Brute Force Method : Duplicate Element is : " + strArray [ j ]); }}} // using Hashset HashSet<String> hs = new HashSet<String>(); for (String arrayElement : strArray ) { if (! hs .add( arrayElement )) {System. out .println( "HashSet :Duplicate Elemen t is : " + arrayElement ); }} ------------------------------------------------------------------------ ------------------------------- LazyQA.com 1 2 . Reverse each word in a sentence Input = "reverse each word in a string"; Output = "esrever hcae drow ni a gnirts" public static void main(String[] args ) { String str = " reverse each word in a string" ; String words [] = str .split( " \ \ s" ); String reverseWord = "" ; for (String w : words ) { StringBuilder sb = new StringBuilder( w ); sb .reverse(); reverseWord = reverseWord + sb .toString() + " " ; } System. out .println( reverseWord .tr im()); } ------------------------------------------------------------------ -------------------------------------- 13. String Anagrams: Determine if two str ings are anagrams of each other Input = String str1 = "Army"; String str2 = "Mary"; Output = army and mary are anagram. public static void main(String[] args ) { String str1 = "Army" ; String str2 = "Mary" ; str1 = str1 .toLowerCase(); str2 = str2 .toLowerCase(); // check if length is same if ( str1 .length() == str2 .length()) { // convert strings to char array char [] charArray1 = str1 .toCharArray(); char [] charArray2 = str2 .toCharArray(); // sort the char array Arrays. sort ( charArray1 ); Arrays. s ort ( charArray2 ); // if sorted char arrays are same, then the string is anagram boolean result = Arrays. equals ( charArray1 , charArray2 ); if ( result ) { System. out .println( str1 + " and " + str2 + " are anagram." ); } else { System. out .println( str1 + " and " + str2 + " are not anagram." ); } } else { System. out .println( str1 + " and " + str2 + " are not anagram." ); } ------------------------------------------------------------------------- ------------------------------- LazyQA.com 14. How to print duplicate charact ers from the string? Input = "apple is fruit"; Output = p i public static void main(String[] args ) { String str = "apple is fruit" ; char [] carray = str .toCharArray(); Sys tem. out .println( "The string is:" + str ); System. out .print( "Duplicate Characters in above string are: " ); for ( int i = 0; i < str .length(); i ++) { for ( int j = i + 1; j < str .length(); j ++) { if ( carray [ i ] == carray [ j ]) { System. out .print( carray [ j ] + "" ); break ; } } } } -------------------------------------------------------------------------------------------------------- 1 5 . Find and print the largest element in an arra y. // Initialize array int [] arr = new int [] { 25, 11, 7, 75, 56 }; // Initialize max with first element of array. int max = arr [0]; // Loop through the array for ( int i = 0; i < arr . length ; i ++) { // Compare elements of array with max if ( arr [ i ] > max ) ma x = arr [ i ]; } System. out .println( "Largest element present in given array: " + max ); -------------------------------------------------------------------------------------------------------- 1 6 . J ava program to split an alphanumeric digit without using split method Input = "Welcome234To567Java89Programming0@#!!"; Output = WelcomeToJavaProgramming 234567890 @#!! public static void main(String[] args ) { String str = "Welcome234To567Java89Programming0@#!!" ; StringBuffer alpha = new StringBuffer(), num = new StringBuffer(), special = new StringBuffer(); for ( int i = 0; i < str .length(); i ++) { LazyQA.com if (Character. isDigit ( str .charAt( i ))) num .append( str .charAt( i )); else if (Character. isAlphabetic ( str .charAt( i ))) alpha .append( str .charAt( i )); else special .append( str .charAt( i )); } System. out .println( alpha ); System. out .println( num ); System. out .println( special ); }
