Check out example codes for "how to compile and run java package program". It will help you in understanding the concepts better.

Code Example 1

package animals;
/* File name : MammalInt.java */
public class MammalInt implements Animal {
   public void eat() {
      System.out.println("Mammal eats");
   }
   public void travel() {
      System.out.println("Mammal travels");
   }
   public int noOfLegs() {
      return 0;
   }
   public static void main(String args[]) {
      MammalInt m = new MammalInt();
      m.eat();
      m.travel();
   }
}

Code Example 2

/* File name : Animal.java */
package animals;
interface Animal {
   public void eat();
   public void travel();
}

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