Editing Constructor (object-oriented programming) (section)

=== Java ===
In [[Java (programming language)|Java]], constructors differ from other methods in that:

* Constructors never have an explicit return type.
* Constructors cannot be directly invoked (the keyword “<code>new</code>” invokes them).
* Constructors should not have non-access modifiers.

Java constructors perform the following tasks in the following order:

# Call the default constructor of the superclass if no constructor is defined.
# Initialize member variables to the specified values.
# Executes the body of the constructor.

Java permit users to call one constructor in another constructor using <code>this()</code> keyword.
But <code>this()</code> must be first statement. <ref>{{Cite web|url=https://ranjeetkumarmaurya.wordpress.com/2017/02/06/constructor-in-java/|title=Details on Constructor in java}}</ref>

<syntaxhighlight lang="java">
class Example
{ 
    Example() // Non-parameterized constructor
    {
        this(1);  // Calling of constructor
        System.out.println("0-arg-cons");
    }
    Example(int a) // Parameterized constructor
    {
        System.out.println("1-arg-cons");
    }
}
public static void main(String[] args)
{
  Example e = new Example();
}
</syntaxhighlight>

Java provides access to the [[superclass (computer science)|superclass's]] constructor through the <code>super</code> keyword.

<syntaxhighlight lang="java">
public class Example
{
    // Definition of the constructor.
    public Example()
    {
        this(1);
    }

    // Overloading a constructor
    public Example(int input)
    {
        data = input; // This is an assignment
    }

    // Declaration of instance variable(s).
    private int data;
}
</syntaxhighlight>

<syntaxhighlight lang="java">
// Code somewhere else
// Instantiating an object with the above constructor
Example e = new Example(42);
</syntaxhighlight>

A constructor taking zero number of arguments is called a "no-arguments" or "no-arg" constructor.<ref>{{cite web|url=http://docs.oracle.com/javase/tutorial/java/javaOO/constructors.html|title= Providing Constructors for Your Classes |publisher=Oracle Corporation|date=2013|access-date=2013-12-20}}</ref>