We often need to convert a list to a map in Java. In this lesson, you will learn how to do that with Java 8. If you are looking for more information on working with maps in Java, check out our tutorial on Map in Java. Let’s say we have a list of User objects. …
Read More Convert List to Map in Javapublic class Test { public static void main(String[] args) { Integer[] array = new Integer[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; // reverse an array Integer[] reversedArray = reverse(array); // print the elements Arrays.stream(reversedArray).forEach(item -> System.out.print(item + ” “)); } public static Integer[] reverse(Integer[] array) { List arrayList = Arrays.asList(array); Collections.reverse(arrayList); return…
Read More Reverse an Array in Javapublic class Test {z public static void main(String[] args) { List<Integer> numbers = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)); Collections.reverse(numbers); System.out.println(numbers); } } Output: [10, 9, 8, 7, 6, 5, 4, 3, 2, 1] Reverse a List using List.add() and List.remove() methods public class Test { public static void main(String[]…
Read More Reverse a List in Javaimport java.util.*; public class Test { public static void main(String[] args) { List<String> names = new ArrayList<>(Arrays.asList(“Megan”, “Tom”, “Steve”, “Megan”, “Meliisa”, “Tom”, “John”)); Set<String> uniqueNames = new HashSet<>(names); // creating a Set from the List System.out.println(uniqueNames); } } Output: [Megan, Tom, Steve, John, Meliisa] Remove duplicates from a List in Java using the Java 8…
Read More Remove Duplicates from a List in Javaimport java.util.*; public class Test { public static void main(String[] args) { List<Integer> numbers = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)); System.out.println(numbers.stream().mapToInt(Integer::intValue).average().getAsDouble()); } } Output: 5.5 Here, we used the mapToInt(Integer::intValue) to convert the Stream<Integer> which is the result of the stream() method, to IntStream. import java.util.*; public class…
Read More Find the Average of Numbers in Javapublic class Test { public static void main(String[] args) { int[] array = new int[]{7, 1, 9, 2, 5}; Arrays.sort(array); Arrays.stream(array).forEach(System.out::print); } } Output: 1 2 5 7 9 Note: values of type int will be automatically converted to the corresponding Wrapper class. And since the Integer Wrapper class implements Comparable, we can sort…
Read More Sort an Array in Javaimport java.util.*; public class Test { public static void main(String[] args) { List<Integer> numbers = new ArrayList<>(Arrays.asList(7, 12, 5, 28, 97, 14, 2, 7, 8, 12, 19, 22)); Collections.sort(numbers); System.out.println(numbers); } } Output: [2, 5, 7, 7, 8, 12, 12, 14, 19, 22, 28, 97] Using the sort() method from ArrayList class public class Test…
Read More Sort a List in Javaclass Test { public static void main(String[] args) { Map<Integer, String> map = new HashMap<>(); map.put(1, “Java”); map.put(7, “Python”); map.put(10, “Ruby”); map.put(3, “Kotlin”); for (Map.Entry<Integer, String> entry : map.entrySet()) { System.out.println(“Key = ” + entry.getKey() + “, Value = ” + entry.getValue()); } } } Output: Key = 1, Value = Java Key = 3,…
Read More Iterate over a Map in Javapublic class Test { public static void main(String[] args) { System.out.println(factorial(5)); } static int factorial(int num) { if (num == 1) { return 1; } else return (num * factorial(num – 1)); } } Output: 120 This code defines a static method named “factorial” that takes an integer argument and calculates the factorial of…
Read More Find Factorial of a Number in Javapublic class Test { public static void main(String[] args) { int num = 8; int num2 = 9; if(num % 2 == 0) { System.out.println(“num is an even number!”); } else { System.out.println(“num is odd number!”); } if(num2 % 2 == 0) { System.out.println(“num2 is an even number!”); } else { System.out.println(“num2 is odd number!”);…
Read More Check if the Number is Even or Odd in Javapublic class Test { public static void main(String[] args) { String str = “racecar”; System.out.println(str.equals(new StringBuilder(str).reverse().toString())); } } Output: true We can do the same with the StringBuffer class since it also has the reverse() method. Using the for loop public class Test { public static void main(String[] args) { String str = “racecar”;…
Read More Check if String is Palindrome in Javapublic class Test { public static void main(String[] args) { String str1 = “Learn Java Programming with alegrucoding.com”; String str2 = “Learn Java”; String str3 = “Simple Java Programming”; // check if str1 contains str2 if (str1.contains(str2)) { System.out.println(“str2 is present in str1”); } else { System.out.println(“str2 is not present in str1”); } // check…
Read More Check if a String Contains a Substring in Javapublic class Test { public static void main(String[] args) { // create an object of Random class Random random = new Random(); // Generate random integer 0 to 100 int randomInteger1 = random.nextInt(101); // Generate random integer 0 to 10000 int randomInteger2 = random.nextInt(10001); // Generate random double value double randomDouble = random.nextDouble(); // Generate…
Read More Generate a Random Number in Javapublic class Test { public static void main(String[] args) { List<Integer> list = new ArrayList<>(Arrays.asList(7, 19, 14, 1, 12, 22, 18, 3, 28, 5)); System.out.println(“Maximum value: ” + Collections.max(list)); System.out.println(“Minimum value: ” + Collections.min(list)); } } Output: Maximum value: 28 Minimum value: 1 Finding the maximum and minimum values in List using the Java 8…
Read More Find Max and Min Values of a List in Java