Interfaces - Beginning Java 8 Fundamentals - page 675

Sometimes an interface may want to access the override default methods of its superinterfaces. Java 8 introduced
a new syntax for calling the overridden default methods of direct superinterfaces from an interface. The new syntax
uses the keyword super as shown:

SuperInterfaceName.super.superInterfaceDefaultMethod(arg1, arg2...)

■ Using the keyword super , only the default methods of the direct superinterfaces can be accessed. accessing
default methods of the superinterfaces of superinterfaces are not supported by the syntax. You cannot access the abstract
methods of the superinterfaces using this syntax.

Tip

Listing 17-31 contains the declaration for the SingerPlayer that resolves the conflict by overriding the getRate()
method with a default getRate() method. The method calls the getRate() method of the Player interface using
the Player.super.getRate() call, multiplies the value by 3.5, and returns it. It simply implements a rule that a
SingerPlayer is paid minimum 3.5 times a Player is paid. Any class implementing the SingerPlayer interface will
inherit the default implementation of the getRate() method.

Listing 17-31. Overriding the Conflicting Method with a Default Method That Calls the Method in the Superinterface
// SingerPlayer.java
package com.jdojo.interfaces;

public interface SingerPlayer extends Singer, Player{
// Override the getRate() method with a default method that calls the
// Player superinterface getRate() method
@Override
default double getRate() {
double playerRate = Player.super.getRate();
double singerPlayerRate = playerRate * 3.5;
return singerPlayerRate;
}
}

Listing 17-32 contains the code for the CharitySingerPlayer interface. It overrides the setRate() method
with an abstract method and the getRate() method with a default method. The getRate() method calls the default
getRate() method of the Player interface.

Listing 17-32. Overriding the Conflicting Methods in the CharitySinger Interface

// CharitySingerPlayer.java
package com.jdojo.interfaces;

public interface CharitySingerPlayer extends CharitySinger, Player {
// Override the setRate() method with an abstract method
@Override
void setRate(double rate);

// Override the getRate() method with a default method that calls the
// Player superinterface getRate() method
@Override