where do we use interface in java code example

Example 1: Interface in java

// interface in java example
interface Vehicle
{
   public void accelerate();
}
class BMW implements Vehicle
{
   public void accelerate()
   {
      System.out.println("BMW accelerating...");
   }
}
public class InterfaceDemo
{
   public static void main(String[] args)
   {
      BMW obj = new BMW();
      obj.accelerate();
   }
}

Example 2: why we use interface in java

interface Animal {
   void child();
}
class Cat implements Animal {
   public void child() {
      System.out.println("kitten");
   }
}
class Dog implements Animal {
   public void child() {
      System.out.println("puppy");
   }
}
public class LooseCoupling{
   public static void main(String args[]) {
      Animal obj = new Cat();
      obj.child();
   }
}