Our goal in this tutorial is to introduce and explain the various algorithms and utilities provided by the Java Collections class. We will be focusing on the methods used for sorting, searching, and modifying collections in different ways.
By the end of this tutorial, you will have a better understanding of the collection algorithms and utilities. You will learn how to use the various methods provided by the Java Collections class to sort, search, and modify collections.
This tutorial assumes that you have a basic understanding of Java programming, including concepts like classes, objects, and data structures.
The Collections class in Java provides several methods for operating on collections. These include:
Collections.sort() method is used to sort elements in a list.Collections.binarySearch() method is used to search for an element in a sorted list.Collections.reverse() for reversing the order of elements and Collections.shuffle() for randomly rearranging elements.The Collections.sort() method sorts the elements of a list according to their natural ordering. If the elements do not implement the Comparable interface, you need to provide a Comparator.
List<Integer> numbers = new ArrayList<>(Arrays.asList(3, 1, 4, 1, 5, 9));
Collections.sort(numbers);
System.out.println(numbers); // prints [1, 1, 3, 4, 5, 9]
The Collections.binarySearch() method performs a binary search on a sorted list and returns the index of the element if it is found.
int index = Collections.binarySearch(numbers, 4);
System.out.println(index); // prints 3
The Collections.reverse() method reverses the order of elements in a list, and the Collections.shuffle() method randomly rearranges the elements.
Collections.reverse(numbers);
System.out.println(numbers); // prints [9, 5, 4, 3, 1, 1]
Collections.shuffle(numbers);
System.out.println(numbers); // output varies
List<String> fruits = new ArrayList<>(Arrays.asList("Apple", "Banana", "Cherry"));
Collections.sort(fruits);
System.out.println(fruits); // prints [Apple, Banana, Cherry]
Here, we create a list of strings and sort it using the Collections.sort() method. The strings are sorted in lexicographic (alphabetical) order.
int index = Collections.binarySearch(fruits, "Cherry");
System.out.println(index); // prints 2
In this example, we perform a binary search for the string "Cherry" in the sorted list. The method returns the index of the string in the list.
Collections.reverse(fruits);
System.out.println(fruits); // prints [Cherry, Banana, Apple]
Here, we reverse the order of elements in the list using the Collections.reverse() method.
In this tutorial, we learned about the methods provided by the Java Collections class for sorting, searching, and modifying collections. We also saw examples of how to use these methods in code.
To further your understanding, you might want to explore other methods provided by the Collections class, such as Collections.max(), Collections.min(), and Collections.rotate().
Solution to Exercise 1
List<Integer> numbers = new ArrayList<>(Arrays.asList(3, 1, 4, 1, 5, 9));
Collections.sort(numbers, Collections.reverseOrder());
System.out.println(numbers); // prints [9, 5, 4, 3, 1, 1]
Here, we use the Collections.sort() method with a reverse order comparator to sort the list in descending order.
Solution to Exercise 2
int index = Collections.binarySearch(numbers, 5, Collections.reverseOrder());
System.out.println(index); // prints 1
In this solution, we perform a binary search for the integer 5 in the sorted list. We provide a reverse order comparator because the list is sorted in descending order.
Solution to Exercise 3
Collections.reverse(numbers);
System.out.println(numbers); // prints [1, 1, 3, 4, 5, 9]
Finally, we reverse the order of elements in the list using the Collections.reverse() method.