A lecture snippet with a mentor as part of the Codegym University course. Sign up for the full course.

"Now it's high time that I tell you about constructors. This is really simple concept. Programmers have invented a shorthand way to create and initialize objects."

Without a constructor With a constructor 
MyFile file = new MyFile();
file.initialize("c:\data\a.txt");
String text = file.readText();
 
MyFile file = new MyFile("c:\data\a.txt");
String text = file.readText();
 
MyFile file = new MyFile();
file.initialize("c:\data\", "a.txt");
String text = file.readText();
 
MyFile file = new MyFile("c:\data\", "a.txt");
String text = file.readText();
 
MyFile file = new MyFile();
file.initialize("c:\data\a.txt");

MyFile file2 = new MyFile();
file2.initialize( MyFile file, "a.txt");
String text = file2.readText();
 
MyFile file = new MyFile("c:\data\a.txt");


MyFile file2 = new MyFile(file, "a.txt");
String text = file2.readText();

"I just finished learning about the initialize method…"

"Look harder. With constructors, the code is more convenient and compact."

"So it is. Here's a question. I know how to write an initialize method inside a class, but how do I write a constructor?"

"First, look at this example:"

Without a constructor With a constructor 
class MyFile
{
  private String filename = null;

  public void initialize(String name)
  {
    this.filename = name;
  }

  public void initialize(String folder, String name)
  {
    this.filename = folder + name;
  }

  public void initialize(MyFile file, String name)
  {
    this.filename = file.getFolder() + name;
  }

…
}
 
class MyFile
{
  private String filename = null;

  public MyFile(String name)
  {
    this.filename = name;
  }

  public MyFile(String folder, String name)
  {
    this.filename = folder + name;
  }

  public MyFile(MyFile file, String name)
  {
    this.filename = file.getFolder() + name;
  }

…
}

"It's easy to declare a constructor inside a class. A constructor is similar to the initialize method, with just two differences:

1. The name of a constructor is the same as the class name (instead of initialize).

2. A constructor has no type (no type is indicated)."

"OK, so it's like initialize, but with a few differences. I think I get it."