biking.java

Thinking in Java第四版 课后习题的源码

// polymorphism/biking/Biking.java
// TIJ4 Chapter Polymorphism, Exercise 1, page 281
/* Create a Cycle class, with subclasses Unicycle, Bicycle and Tricycle. 
* Demonstrate that an instance of each type can be upcast to Cycle via a ride()
* method.
*/
package polymorphism.biking;
import static org.greggordon.tools.Print.*;

class Cycle {
	private String name = "Cycle";
	public static void travel(Cycle c) {
		println("Cycle.ride() " + c);
	}
	public String toString() {
		return this.name;
	}
}

class Unicycle extends Cycle {
	private String name = "Unicycle";
	public String toString() {
		return this.name;
	}	
}

class Bicycle extends Cycle {
	private String name = "Bicycle";
	public String toString() {
		return this.name;
	}	

}

class Tricycle extends Cycle {
	private String name = "Tricycle";
	public String toString() {
		return this.name;
	}	
}

public class Biking {
	public static void ride(Cycle c) {
		c.travel(c);
	}
	public static void main(String[] args) {
		Unicycle u = new Unicycle();
		Bicycle b = new Bicycle();
		Tricycle t = new Tricycle();
		ride(u);
		ride(b);
		ride(t);		
	}
}