Understanding Parameterized Constructors in Java

package ch7.l7;

class Rectangle {
    double length;
    double width;
 
    // Parameterized constructor
    public Rectangle(double l, double w) {
        length = l;
        width = w;
    }
    //Method to Calculate Area
    double calculateArea() {
        return length * width;
    }
}
 
public class RectangleMain {
    public static void main(String[] args) {
    	
        Rectangle rect1 = new Rectangle(5.0, 3.0);
        Rectangle rect2 = new Rectangle(5.0, 3.0);
        
        System.out.println("Area of rect1: " + rect1.calculateArea());
        System.out.println("Area of rect 2: " + rect2.calculateArea());
    }
}

Area of rect1: 15.0
Area of rect 2: 450.0

class Student {
    private String name;
    private int age;

    public Student(String name, int age) {
        this.name = name;
        if (age >= 0 && age <= 150) { // Data validation
            this.age = age;
        } else {
            System.out.println("Invalid age for student " + name + ". Setting age to 0.");
            this.age = 0; // Or throw an exception
        }
    }

    // Getters
    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

public class ParameterizedConstructorExample2 {
    public static void main(String[] args) {
        Student student1 = new Student("Alice", 20);
        System.out.println("Student 1: Name = " + student1.getName() + ", Age = " + student1.getAge());

        Student student2 = new Student("Bob", -5); // Invalid age
        System.out.println("Student 2: Name = " + student2.getName() + ", Age = " + student2.getAge()); // Age will be 0

        Student student3 = new Student("Charlie", 160); // Invalid age
        System.out.println("Student 3: Name = " + student3.getName() + ", Age = " + student3.getAge()); // Age will be 0

    }
}

Rectangle 1: Length = 10, Width = 5
Area = 50
Rectangle 2: Length = 7, Width = 12
Area = 84