why use an interface 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: how to declare a interface in java

// Assume we have the simple interface:
interface Appendable {
	void append(string content);
}
// We can implement it like that:
class SimplePrinter implements Appendable {
 	public void append(string content) {
   		System.out.println(content); 
    }
}
// ... and maybe like that:
class FileWriter implements Appendable {
 	public void append(string content) {
   		// Appends content into a file 
    }
}
// Both classes are Appendable.
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how to implement a interface in java

Example 3: creating the functional interface in java

package com.concretepage;

@FunctionalInterface
public interface Calculator {
   long calculate(long num1, long num2);
}