Interfaces - Beginning Java 8 Fundamentals - page 672

@Override
default double getRate() {
return 0.0;
}
}
The setRate() method is a no-op. The getRate() method returns zero. The class that implements the
CharitySinger interface will need to implement the sing() method and provide an implementation for it. The class
will inherit the default methods setRate() and getRate() .
It is possible that the same person is a singer as well as a writer. You can create an interface named SingerWriter ,
which inherits from the two interfaces Singer and Writer , as shown in Listing 17-27.
Listing 17-27. A SingerWriter Interface That Inherits from Singer and Writer Interfaces
// SingerWriter.java
package com.jdojo.interfaces;
public interface SingerWriter extends Singer, Writer {
// No code
}
How many methods does the SingerWriter interface have? It inherits three abstract methods from the Singer
interface and three abstract methods from the Writer interface. It inherits methods setRate() and getRate()
twice - once from the Singer interface and once from the Writer interface. These methods have the same declarations
in both superinterfaces and they are abstract. This does not cause a problem as both methods are abstract. The class
that implements the SingerWriter interface will need to provide implementation for both methods only once.
Listing 17-28 shows the code for a Melodist class that implements the SingerWriter interface. Note that it
overrides the setRate() and getRate() methods only once.
Listing 17-28. A Melodist Class That Implements the SingerWriter Interface
// Melodist.java
package com.jdojo.interfaces;
public class Melodist implements SingerWriter {
private String name;
private double rate = 500.00;
public Melodist(String name) {
this.name = name;
}
@Override
public void sing() {
System.out.println(name + " is singing.");
}
@Override
public void setRate(double rate) {
this.rate = rate;
}