Learn JAVA with Real Code Examples

import java.util.*;
import java.util.stream.Collectors;

public class StreamExample {
    public static void main(String[] args) {
        List<String> names = Arrays.asList(
        "Alice", "Bob", "Charlie", "David", "Eve"
        );

        List<String> filteredNames = names.stream()
        .filter(name -> name.length() > 3)
        .map(String::toUpperCase)
        .sorted()
        .collect(Collectors.toList());

        System.out.println("Filtered names: " + filteredNames);

        Optional<String> longest = names.stream()
        .max(Comparator.comparing(String::length));

        longest.ifPresent(name ->
        System.out.println("Longest name: " + name)
        );
    }
}

Shows modern Java features including streams, lambda expressions, and collection operations.

class Person {
    String name;
    int age;

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

    void introduce() {
        System.out.println("Hi, I'm " + name + ", age " + age);
    }
}

public class Main {
    public static void main(String[] args) {
        Person p = new Person("Alice", 25);
        p.introduce();
    }
}

Defines a class with properties and methods and demonstrates object creation.

import java.util.*;

public class MapExample {
    public static void main(String[] args) {
        Map<String, Integer> ages = new HashMap<>();
        ages.put("Alice", 25);
        ages.put("Bob", 30);

        for(Map.Entry<String, Integer> entry : ages.entrySet()) {
        System.out.println(entry.getKey() + " is " + entry.getValue() + " years old");
        }
    }
}

Demonstrates using HashMap, adding entries, and iterating over keys and values.

import java.util.*;

public class SortExample {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(5, 3, 8, 1, 9);
        Collections.sort(numbers);
        System.out.println("Sorted: " + numbers);

        numbers.sort((a, b) -> b - a);
        System.out.println("Reverse sorted: " + numbers);
    }
}

Shows sorting a list of integers using Collections.sort and lambda expressions.

public class ExceptionExample {
    public static void main(String[] args) {
        try {
        int result = 10 / 0;
        } catch (ArithmeticException e) {
        System.out.println("Cannot divide by zero");
        } finally {
        System.out.println("Execution finished");
        }
    }
}

Demonstrates try-catch-finally blocks to handle exceptions safely.

import java.util.*;

public class LambdaExample {
    public static void main(String[] args) {
        List<String> fruits = Arrays.asList("Apple", "Banana", "Cherry");
        fruits.forEach(fruit -> System.out.println(fruit));
    }
}

Iterates over a list using forEach and a lambda expression.

import java.util.*;

public class OptionalExample {
    public static void main(String[] args) {
        Optional<String> name = Optional.ofNullable(null);
        System.out.println(name.orElse("Default Name"));
    }
}

Shows how to use Optional to handle potential null values.

import java.util.*;
import java.util.stream.Collectors;

public class FilterExample {
    public static void main(String[] args) {
        List<Integer> nums = Arrays.asList(1,2,3,4,5,6);
        List<Integer> even = nums.stream()
        .filter(n -> n % 2 == 0)
        .collect(Collectors.toList());
        System.out.println("Even numbers: " + even);
    }
}

Filters a list of integers and collects results using Stream API.

import java.util.*;

public class SetExample {
    public static void main(String[] args) {
        Set<String> set = new HashSet<>();
        set.add("Alice");
        set.add("Bob");
        set.add("Alice"); // Duplicate ignored
        System.out.println(set);
    }
}

Demonstrates usage of HashSet to store unique elements.

import java.util.*;

class Person {
    String name;
    int age;
    Person(String name, int age) { this.name = name; this.age = age; }
    public String toString() { return name + "(" + age + ")"; }
}

public class ComparatorExample {
    public static void main(String[] args) {
        List<Person> people = Arrays.asList(
        new Person("Alice", 25),
        new Person("Bob", 30),
        new Person("Charlie", 20)
        );
        people.sort(Comparator.comparingInt(p -> p.age));
        System.out.println(people);
    }
}

Sorts a list of custom objects using a custom comparator.