In Java, a default constructor is a constructor that takes no arguments. It is also called a no-argument constructor, because it doesn't take any arguments. If no constructor is defined in a class, Java will provide a default constructor that takes no arguments.

Here's an example of a default constructor:

public class MyClass {
    private int value;

    public MyClass() {
        value = 0;
    }

    public int getValue() {
        return value;
    }
}

In this example, we have a class called MyClass with a single field value, and a default constructor that sets the value of the value field to 0. To create an object of MyClass using this constructor, we can use the following code:

MyClass myObj = new MyClass();

This will create a new instance of MyClass, with the value field set to 0.

If you define any constructor explicitly in a class, the default constructor will not be provided by Java. However, if you still want to provide a no-argument constructor in your class, you can define it explicitly like in the example above.

Note that constructors can also be parameterized, which means you can define constructors with one or more parameters, including constructors that take no arguments. This allows you to create objects with different initial values or behaviors depending on the constructor used.