我在使用这个构造函数时遇到问题

Question

Can anyone tell me, what is the mistake that i made in using "this" constructor, inside the constructor public Student(). Please tell me how to correct it. Compiler is showing this error -

Error:(10, 11) java: constructor Student in class com.shreyansh.Student cannot be applied to given types; required: no arguments found: int,java.lang.String reason: actual and formal argument lists differ in length

****The code is shown here****

package com.shreyansh;

import java.util.Scanner;

public class Student {
      private int rno;
      private String name;

      public Student() {
          this(0, "Not defined"); //what is the error in this line
      }

      public void enter() {
          System.out.println("Enter name of the student - ");
          Scanner scanner = new Scanner(System.in);
          this.name=scanner.nextLine();
          System.out.println("Enter the roll number - ");
          this.rno=scanner.nextInt();
          scanner.close();
      }
      public void show() {
          System.out.println("The name of the student is - "+name);
          System.out.println("And the roll number is - "+rno);
      }
}

Answer 1

When you call a constructor from another constructor, you must define the constructor you are calling:

Adding this constructor:

public Student(int rno, String name) {
    this.rno = rno;
    this.name = name;
}

will allow the

this(0, "Not defined");

call to pass compilation.

Answer 2

public Student() {
          this(0, "Not defined"); //what is the error in this line
      }

What that tries to do, is call a constructor in the same class, with those parameters. In order for that to work, this constructor must be there:

public Student (int rno, String name) {
  this.rno = rno;
  this.name = name;
}

but you don't have such a constructor, so change your current constructor to:

public Student() {
  this.rno = 0;
  this.name = "Not defined";
}

or, add the second constructor.

Answer 3

When you are using this inside your constructor, you are calling another constructor inside your class, but you don't actually have any other constructor that has such arguments, so you should create another constructor with said parameters like this:

public Student(int rno, String name) 
{
   this.rno = rno;
   this.name;
}

Answer 4

the problem is the way you creating your object. your constructor must be like:

public Student() {
       // you have to indicate the value of each variable here
      this.rno = 0; 
      this.name = "name";
}