Introduction To Java Programming Language

Answer: (iii) An object is created

A constructor runs when an object is instantiated with new (or through another constructor). It initializes the new object's state. Constructors have the class name and no return type.

class Student {
    Student() { System.out.println("Created"); }
}
Student s = new Student(); // invokes constructor

Find highest, lowest and average marks

public class Marks {
    public static void main(String[] args) {
        int[] marks = {72, 85, 61, 90, 77}; // example values
        int max = marks[0], min = marks[0], sum = 0;
        for (int mark : marks) {
            if (mark > max) max = mark;
            if (mark < min) min = mark;
            sum += mark;
        }
        double average = (double) sum / marks.length;
        System.out.println("Highest = " + max);
        System.out.println("Lowest = " + min);
        System.out.println("Average = " + average);
    }
}

Replace the example array with the 50 students' marks. Initializing max and min from the first element avoids assuming marks are non-negative. A single pass calculates all three values: O(n) time and O(1) extra space.

== versus .equals()

String s1 = "Java";
String s2 = new String("Java");

• s1 == s2 is false because == compares object references, and new String(...) creates a distinct object.
• s1.equals(s2) is true because String.equals() compares character contents.

For strings, use .equals() when comparing text. == is appropriate when reference identity is what you intend to test.

Constructors and object creation

A constructor initializes an object's state. It has the same name as its class and no return type. Constructors may be no-argument, parameterized, or overloaded; if no constructor is declared, Java supplies a default no-argument constructor.

class Book {
    String title;
    Book(String title) { this.title = title; }
}
Book b = new Book("Networks");

new allocates an object, initializes its fields to default values, and invokes the selected constructor. this(...) calls another constructor in the same class and must be first; super(...) calls a superclass constructor and must also be first.