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C

Collection Programs

Working with lists, sets, and maps hands-on is the best way to become comfortable with the Collection Framework for real projects and interviews.

Why practice these?

Working with lists, sets, and maps hands-on is the best way to become comfortable with the Collection Framework for real projects and interviews.

Program 1: Remove Duplicates from a List Using a Set

java
import java.util.*;

public class RemoveDuplicates {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 2, 3, 4, 4, 5);
        Set<Integer> uniqueNumbers = new LinkedHashSet<>(numbers);

        System.out.println(uniqueNumbers);
    }
}

Output:

[1, 2, 3, 4, 5]

Program 2: Count Word Frequency Using a Map

java
import java.util.*;

public class WordFrequency {
    public static void main(String[] args) {
        String[] words = {"apple", "banana", "apple", "orange", "banana", "apple"};
        Map<String, Integer> frequency = new HashMap<>();

        for (String word : words) {
            frequency.put(word, frequency.getOrDefault(word, 0) + 1);
        }
        System.out.println(frequency);
    }
}

Output:

{banana=2, orange=1, apple=3}

Program 3: Sort a List of Names Alphabetically

java
import java.util.*;

public class SortNames {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>(Arrays.asList("Riya", "Aman", "Karan"));
        Collections.sort(names);
        System.out.println(names);
    }
}

Output:

[Aman, Karan, Riya]

Key Points to Remember

  • getOrDefault() is a handy HashMap method for counting occurrences without extra null-checking code.
  • Converting a List into a Set is a quick, common way to remove duplicates.
  • Collections.sort() is the standard way to sort a List using its natural ordering.