Java Functional Interface.

Java functional interface

• A functional interface is simply an interface that has exactly one abstract method.
• A functional interface is to be used by Lambda Expression.
• The following types of members in an interface do NOT count for defining a functional interface:
  • Default methods.
  • Static methods.
  • Public methods inherited from the Object class.
  • Constants.

  @FunctionalInterface // This is not required 
  public interface Percentage { 
    static final double MAX = 100, MIN = 0; // It is allowed to have  constants
    public double getPercentage(double amounts, double value);  // the abstract method
    // It is allowed to override methods in Object class 
   @Override
    public boolean equals(Object obj);  
    default public double getMaxAdjusted() { // It is allowed to have default methods
      return MAX - 10;
    }
    static public double getMinPercentage() { // It is allowed to have static methods
      return MIN + 10;
    }
  }