初始化

//: c07:PolyConstructors.java
// Constructors and polymorphism
// don't produce what you might expect.
import com.bruceeckel.simpletest.*;

abstract class Glyph {
	abstract void draw();

	Glyph() {
		System.out.println("Glyph() before draw()");
		draw();
		System.out.println("Glyph() after draw()");
	}
}

class RoundGlyph extends Glyph {
	private int radius = 1;

	RoundGlyph(int r) {
		radius = r;
		System.out.println("RoundGlyph.RoundGlyph(), radius = " + radius);
	}

	void draw() {
		System.out.println("RoundGlyph.draw(), radius = " + radius);
	}
}

public class PolyConstructors {
	private static Test monitor = new Test();

	public static void main(String[] args) {
		new RoundGlyph(5);
		monitor.expect(new String[] {
				"Glyph() before draw()",
				"RoundGlyph.draw(), radius = 0", 
				"Glyph() after draw()",
				"RoundGlyph.RoundGlyph(), radius = 5" });	}
} // /:~

初始化的实际过程是：
1. 在其他任何事物发生之前，将分配给对象的存储空间初始化成二进制的零。
2. 如前所述的那样，调用基类构造器。此时，调用被重载的draw()方法（是的，是在调用RoundGlyph构造器之前调用的），由于步骤(1)的缘故，我们此时会发现radius的值为0。
3. 按照声明的顺序调用成员的初始化代码。
4. 调用导出类的构造器主体。