问题在<thinking in java> 3rd ed.的第七章Polymorphism上看到的代码如下(稍有改动)/*abstract*/ class Glyph {
/* abstract*/ void draw(){System.out.println("draw() in Glyph");}
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 {
public static void main(String[] args)
{
new RoundGlyph(5);
}
}输出:
Glyph() before draw()
RoundGlyph.draw(), radius = 0
Glyph() after draw()
RoundGlyph.RoundGlyph(), radius = 5问题1:对为何会调用RoundGlyph中的draw()而不是Glyph中的draw()不是很理解.
2:编译器是先为需要构造的object分配所有的空间然后进行默认的赋值,还是按照构造函数调用的顺序分配空间?
/* abstract*/ void draw(){System.out.println("draw() in Glyph");}
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 {
public static void main(String[] args)
{
new RoundGlyph(5);
}
}输出:
Glyph() before draw()
RoundGlyph.draw(), radius = 0
Glyph() after draw()
RoundGlyph.RoundGlyph(), radius = 5问题1:对为何会调用RoundGlyph中的draw()而不是Glyph中的draw()不是很理解.
2:编译器是先为需要构造的object分配所有的空间然后进行默认的赋值,还是按照构造函数调用的顺序分配空间?
我当然知道是dynamic-binding