java-array-list examples

import java.util.ArrayList;
import java.util.List;

public class AccessElementsFromArrayListExample {
    public static void main(String[] args) {
        List<String> topCompanies = new ArrayList<>();

        // Check if an ArrayList is empty
        System.out.println("Is the topCompanies list empty? : " + topCompanies.isEmpty());

        topCompanies.add("Google");
        topCompanies.add("Apple");
        topCompanies.add("Microsoft");
        topCompanies.add("Amazon");
        topCompanies.add("Facebook");

        // Find the size of an ArrayList
        System.out.println("Here are the top " + topCompanies.size() + " companies in the world");
        System.out.println(topCompanies);

        // Retrieve the element at a given index
        String bestCompany = topCompanies.get(0);
        String secondBestCompany = topCompanies.get(1);
        String lastCompany = topCompanies.get(topCompanies.size() - 1);

        System.out.println("Best Company: " + bestCompany);
        System.out.println("Second Best Company: " + secondBestCompany);
        System.out.println("Last Company in the list: " + lastCompany);

        // Modify the element at a given index
        topCompanies.set(4, "Walmart");
        System.out.println("Modified top companies list: " + topCompanies);
    }
}

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import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class ArrayListCollectionsSortExample {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>();
        numbers.add(13);
        numbers.add(7);
        numbers.add(18);
        numbers.add(5);
        numbers.add(2);

        System.out.println("Before : " + numbers);

        // Sorting an ArrayList using Collections.sort() method
        Collections.sort(numbers);

        System.out.println("After : " + numbers);
    }
}
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import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class ArrayListIteratorRemoveExample {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>();
        numbers.add(13);
        numbers.add(18);
        numbers.add(25);
        numbers.add(40);

        Iterator<Integer> numbersIterator = numbers.iterator();
        while (numbersIterator.hasNext()) {
            Integer num = numbersIterator.next();
            if(num % 2 != 0) {
                numbersIterator.remove();
            }
        }

        System.out.println(numbers);
    }
}
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import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

class Person {
    private String name;
    private Integer age;

    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

public class ArrayListObjectSortExample {
    public static void main(String[] args) {
        List<Person> people = new ArrayList<>();
        people.add(new Person("Sachin", 47));
        people.add(new Person("Chris", 34));
        people.add(new Person("Rajeev", 25));
        people.add(new Person("David", 31));

        System.out.println("Person List : " + people);

        // Sort People by their Age
        people.sort((person1, person2) -> {
            return person1.getAge() - person2.getAge();
        });

        // A more concise way of writing the above sorting function
        people.sort(Comparator.comparingInt(Person::getAge));

        System.out.println("Sorted Person List by Age : " + people);

        // You can also sort using Collections.sort() method by passing the custom Comparator
        Collections.sort(people, Comparator.comparing(Person::getName));
        System.out.println("Sorted Person List by Name : " + people);
    }
    
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import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

public class ArrayListSortExample {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Lisa");
        names.add("Jennifer");
        names.add("Mark");
        names.add("David");

        System.out.println("Names : " + names);

        // Sort an ArrayList using its sort() method. You must pass a Comparator to the ArrayList.sort() method.
        names.sort(new Comparator<String>() {
            @Override
            public int compare(String name1, String name2) {
                return name1.compareTo(name2);
            }
        });

        // The above `sort()` method call can also be written simply using lambda expression
        names.sort((name1, name2) -> name1.compareTo(name2));

        // Following is an even more concise solution
        names.sort(Comparator.naturalOrder());

        System.out.println("Sorted Names : " + names);
    }
}
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import java.util.ArrayList;
import java.util.List;

class User {
    private String name;
    private int age;

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

public class ArrayListUserDefinedObjectExample {
    public static void main(String[] args) {
        List<User> users = new ArrayList<>();
        users.add(new User("Rajeev", 25));
        users.add(new User("John", 34));
        users.add(new User("Steve", 29));

        users.forEach(user -> {
            System.out.println("Name : " + user.getName() + ", Age : " + user.getAge());
        });
    }
}
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import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

public class ArrayListSortExample {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Lisa");
        names.add("Jennifer");
        names.add("Mark");
        names.add("David");

        System.out.println("Names : " + names);

        // Sort an ArrayList using its sort() method. You must pass a Comparator to the ArrayList.sort() method.
        names.sort(new Comparator<String>() {
            @Override
            public int compare(String name1, String name2) {
                return name1.compareTo(name2);
            }
        });

        // The above `sort()` method call can also be written simply using lambda expression
        names.sort((name1, name2) -> name1.compareTo(name2));

        // Following is an even more concise solution
        names.sort(Comparator.naturalOrder());

        System.out.println("Sorted Names : " + names);
    }
}
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import java.util.ArrayList;
import java.util.List;

public class CreateArrayListExample {

    public static void main(String[] args) {
        // Creating an ArrayList of String using
        List<String> animals = new ArrayList<>();

        // Adding new elements to the ArrayList
        animals.add("Lion");
        animals.add("Tiger");
        animals.add("Cat");
        animals.add("Dog");

        System.out.println(animals);

        // Adding an element at a particular index in an ArrayList
        animals.add(2, "Elephant");

        System.out.println(animals);
    }
}
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import java.util.ArrayList;
import java.util.List;

public class CreateArrayListFromCollectionExample {

    public static void main(String[] args) {
        List<Integer> firstFivePrimeNumbers = new ArrayList<>();
        firstFivePrimeNumbers.add(2);
        firstFivePrimeNumbers.add(3);
        firstFivePrimeNumbers.add(5);
        firstFivePrimeNumbers.add(7);
        firstFivePrimeNumbers.add(11);

        // Creating an ArrayList from another collection
        List<Integer> firstTenPrimeNumbers = new ArrayList<>(firstFivePrimeNumbers);


        List<Integer> nextFivePrimeNumbers = new ArrayList<>();
        nextFivePrimeNumbers.add(13);
        nextFivePrimeNumbers.add(17);
        nextFivePrimeNumbers.add(19);
        nextFivePrimeNumbers.add(23);
        nextFivePrimeNumbers.add(29);

        // Adding an entire collection to an ArrayList
        firstTenPrimeNumbers.addAll(nextFivePrimeNumbers);

        System.out.println(firstTenPrimeNumbers);
    }
}
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import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;

public class IterateOverArrayListExample {
    public static void main(String[] args) {
        List<String> tvShows = new ArrayList<>();
        tvShows.add("Breaking Bad");
        tvShows.add("Game Of Thrones");
        tvShows.add("Friends");
        tvShows.add("Prison break");

        System.out.println("=== Iterate using Java 8 forEach and lambda ===");
        tvShows.forEach(tvShow -> {
            System.out.println(tvShow);
        });

        System.out.println("\n=== Iterate using an iterator() ===");
        Iterator<String> tvShowIterator = tvShows.iterator();
        while (tvShowIterator.hasNext()) {
            String tvShow = tvShowIterator.next();
            System.out.println(tvShow);
        }

        System.out.println("\n=== Iterate using an iterator() and Java 8 forEachRemaining() method ===");
        tvShowIterator = tvShows.iterator();
        tvShowIterator.forEachRemaining(tvShow -> {
            System.out.println(tvShow);
        });

        System.out.println("\n=== Iterate using a listIterator() to traverse in both directions ===");
        // Here, we start from the end of the list and traverse backwards.
        ListIterator<String> tvShowListIterator = tvShows.listIterator(tvShows.size());
        while (tvShowListIterator.hasPrevious()) {
            String tvShow = tvShowListIterator.previous();
            System.out.println(tvShow);
        }

        System.out.println("\n=== Iterate using simple for-each loop ===");
        for(String tvShow: tvShows) {
            System.out.println(tvShow);
        }

        System.out.println("\n=== Iterate using for loop with index ===");
        for(int i = 0; i < tvShows.size(); i++) {
            System.out.println(tvShows.get(i));
        }
    }
}
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import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;

public class RemoveElementsFromArrayListExample {
    public static void main(String[] args) {
        List<String> programmingLanguages = new ArrayList<>();
        programmingLanguages.add("C");
        programmingLanguages.add("C++");
        programmingLanguages.add("Java");
        programmingLanguages.add("Kotlin");
        programmingLanguages.add("Python");
        programmingLanguages.add("Perl");
        programmingLanguages.add("Ruby");

        System.out.println("Initial List: " + programmingLanguages);

        // Remove the element at index `5`
        programmingLanguages.remove(5);
        System.out.println("After remove(5): " + programmingLanguages);

        // Remove the first occurrence of the given element from the ArrayList
        // (The remove() method returns false if the element does not exist in the ArrayList)
        boolean isRemoved = programmingLanguages.remove("Kotlin");
        System.out.println("After remove(\"Kotlin\"): " + programmingLanguages);

        // Remove all the elements that exist in a given collection
        List<String> scriptingLanguages = new ArrayList<>();
        scriptingLanguages.add("Python");
        scriptingLanguages.add("Ruby");
        scriptingLanguages.add("Perl");

        programmingLanguages.removeAll(scriptingLanguages);
        System.out.println("After removeAll(scriptingLanguages): " + programmingLanguages);

        // Remove if the element matches a given predicate
        programmingLanguages.removeIf(new Predicate<String>() {
            @Override
            public boolean test(String s) {
                return s.startsWith("C");
            }
        });

        /*
            The above removeIf() call can also be written using lambda expression like this -
            programmingLanguages.removeIf(s -> s.startsWith("C"))
        */

        System.out.println("After Removing all elements that start with \"C\": " + programmingLanguages);

        // Remove all elements from the ArrayList
        programmingLanguages.clear();
        System.out.println("After clear(): " + programmingLanguages);
    }
}