Java - lesson 5 | HackIndia Skills

Key point

One idea

A lambda is a short function value. A stream is a clean way to process a collection step by step without writing manual loops for every task.

Where this fits

Your recruiter CLI will have candidate data in lists. You may need to show shortlisted candidates, count skills, sort by score, or print names in a clean format.

You can do all of that with normal for loops. Streams are useful when the job is a pipeline: filter, transform, sort, collect.

Example

Candidate example

Assume your Candidate class has name, city, skills, and score getters. This code finds Java candidates in Bengaluru or remote-ready candidates, sorts by score, and prints a shortlist.

import java.util.Comparator;
import java.util.List;

public class ShortlistService {
    public List<Candidate> shortlist(List<Candidate> candidates) {
        return candidates.stream()
                .filter(candidate -> candidate.getSkills().contains("Java"))
                .filter(candidate -> candidate.getCity().equalsIgnoreCase("Bengaluru")
                        || candidate.isRemoteReady())
                .filter(candidate -> candidate.getScore() >= 70)
                .sorted(Comparator.comparingInt(Candidate::getScore).reversed())
                .toList();
    }

    public void printNames(List<Candidate> candidates) {
        candidates.stream()
                .map(Candidate::getName)
                .forEach(System.out::println);
    }
}

Read the pipeline

Read a stream from top to bottom. stream starts the pipeline. filter keeps only matching items. map changes each item into another value. sorted orders the items. toList creates a new list.

The arrow in candidate -> candidate.getScore() >= 70 is a lambda. It means: for each candidate, return true if their score is at least 70.

Your to-do

Use streams safely

Do each one yourself, then tap it to tick it off. The ticks are only a checklist for you: they are not marked or scored.

Start with a working for loop if the logic is new to you.
Convert one step at a time: first filter, then sort, then map.
Name lambda variables clearly, like candidate, skill, or company.
Collect the result into a list before passing it to your CLI output code.
Run the app after each change so you catch mistakes early.

0 of 5 done

Common mistake

Do not over-chain

A long stream can become harder to read than a loop. If you need many conditions, move them into a method with a clear name.

This is better for reviews. Another builder should understand your repo without asking you on WhatsApp.

private boolean isStrongJavaCandidate(Candidate candidate) {
    return candidate.getSkills().contains("Java")
            && candidate.getScore() >= 70
            && (candidate.getCity().equalsIgnoreCase("Bengaluru")
            || candidate.isRemoteReady());
}

public List<Candidate> shortlist(List<Candidate> candidates) {
    return candidates.stream()
            .filter(this::isStrongJavaCandidate)
            .sorted(Comparator.comparingInt(Candidate::getScore).reversed())
            .toList();
}

Tip

Use AI carefully

You can ask an AI tool to rewrite a loop as a stream. Then check three things yourself: it keeps the same result, it handles empty lists, and it stays readable.

Do not accept code that uses unknown libraries or changes your class names. Your final repo should build cleanly on another laptop.

Prompt:
Rewrite this Java for loop using streams. Keep the same class names and only use the Java standard library. Explain any behavior change.