Initializing and using Interfaces in Java?

Question

First of all, I learned that:

• You cannot instantiate an Interface
• An Interface doesn't implement its functions

After seeing the following Java code:

public class MyClassTest {

    public static void main(String[] args) {

        // String to CharSequence?

        CharSequence c = "Java";

        System.out.println(c);
        System.out.println(c.length());
    }
}

I am very confused when I learned that CharSequence is an Interface

• How can you use an Interface like an object and initialize it?

• Why does CharSequence implements a length function if its an interface?

Answer 1

"Java" is an instance of the String class, which implements the CharSequence interface, which includes implementing the length() method. Therefore you can assign it to a CharSequence variable.

A variable whose type is an interface can be assigned references to instances (objects) of any classes that implement that interface.