ex3.java

java编程思想第四版习题答案

// interfaces/Ex3.java
// TIJ4 Chapter Interfaces, Exercise 3, page 315
/* Create a base class with an abstract print() method that is overridden in a
* derived class. The overridden version of the method prints the value of an int
* variable defined in the derived class. At the point of definition of this
* variable, give it a nonzero value. In the base-class constructor, call this
* method. In main(), create an object of the drived type, and then call its
* print() method. Explain the results.
*/
import static org.greggordon.tools.Print.*;

abstract class Dad {
	protected abstract void print();
	Dad() { print(); }
}

class Son extends Dad {
	private int i = 1;
	@Override protected void print() { println("Son.i = " + i); }
}

public class Ex3 {
	public static void main(String[] args) {
		/* Process of initialization:
		* 1. Storage for Son s allocated and initialized to binary zero
		* 2. Dad() called
		* 3. Son.print() called in Dad() (s.i = 0)
		* 4. Member initializers called in order (s.i = 1)
		* 5. Body of Son() called
		*/
		Son s = new Son();
		s.print();
	}
}