In Java, what is the difference between default constructor and constructor with parameters?

Default Constructor

• The default constructor is a 0-argument constructor that contains a reference to the superclass constructor The parameterless call.
• Assigning default values ​​to newly created objects is the main responsibility of the default constructor.
• Only when the program does not write any constructor, the compiler will write a default constructor in the code.
• The access modifier of a default constructor is always the same as the class modifier, but this rule only applies to "public" and "default"

When does the compiler add a default constructor

• The compiler adds a default constructor in the code only when the programmer adds a default constructor in the code without writing a constructor.
• If the programmer writes any constructor in the code, the compiler will not add any constructor.
• Every default constructor is a 0-argument constructor, but every 0-argument constructor is not a default constructor.

Parameterized constructor

• A parameterized constructor is a constructor that has a specific number of parameters to be passed.
• The purpose of parameterized constructors is to assign specific values ​​that the user wants to instance variables of different objects.
• Parameterized constructors are written explicitly by the programmer.
• The access modifier of a default constructor is always the same as the class modifier, but this rule only applies to the "public" and "default" modifiers.

Example

Real-time demonstration

public class Student {
   int roll_no;
   String stu_name;
   Student(int i, String n) { // Parameterized constructor
      roll_no = i;
      stu_name = n;
   }
   void display() {
      System.out.println(roll_no+" "+stu_name);
   }
   public static void main(String args[]) {
      Student s1 = new Student(1,"Adithya");
      Student s2 = new Student(2,"Jai");
      s1.display();
      s2.display();
   }
}

In the above program, the programmer defines a parameterized constructor with 2 parameters. Now the compiler doesn't add a default constructor to the code, and the programmer doesn't write any 0-argument constructors.

Output

1 Adithya
2 Jai

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