import java.util.*;

class Person {
    String name;

    Person(String name) {
        this.name = name;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Person person)) return false;
        return Objects.equals(name, person.name);
    }
}

public class Main {
    public static void main(String[] args) {
        Map<Person, String> map = new HashMap<>();

        Person p1 = new Person("Alex");
        Person p2 = new Person("Alex");

        map.put(p1, "Developer");

        System.out.println(map.get(p2));
    }
}

final StringBuilder sb = new StringBuilder("Java");
sb.append("!");
System.out.println(sb);

class User {
    final int age;  //1

    User(int age) {
        this.age = age; //2
    }

    void updateAge() {
        age = 30;   //3
    }
}

final StringBuilder sb = new StringBuilder("Java");
sb.append("!"); //можно, результат Java!
sb = new StringBuilder("Other"); // ошибка компиляции

String s = "Java";
s.concat("!"); 
System.out.println(s); //выводит Java, поскольку String immutable

public class Main {
    public static void main(String[] args) {
        System.out.println('A' + 1);
    }
}

public class Main {
    public static void main(String[] args) {
        System.out.println(2 + 3 + "4");
        System.out.println("2" + 3 + 4);
    }
}

class Animal {
    static void info() {
        System.out.println("Animal info");
    }

    void speak() {
        System.out.println("Animal speaks");
    }
}

class Dog extends Animal {
    static void info() {
        System.out.println("Dog info");
    }

    void speak() {
        System.out.println("Dog barks");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal a = new Dog();

        a.info();
        a.speak();
    }
}

class A {
    A() {
        System.out.print("A");
    }
}

class B extends A {
    B() {
        System.out.print("B");
    }
}

public class Main {
    public static void main(String[] args) {
        new B();
    }
}