我有两个接口和一个类来实现它们。在界面中,我展示了一种常用的方法和一种通用的方法。在主要方法中执行它们时,常规方法显示正确结果,但通用方法不会。如果可能的话,你能告诉我,为什么increase_twice()方法没有返回正确的结果?这里是我的代码:在java中实现通用接口方法
Rectangle.java:
public class Rectangle implements TwoDShape {
private double width, height;
public Rectangle (double width, double height) {
this.width = width;
this.height = height;
}
public double area() {
return width * height;
}
public double perimeter() {
return 2.0 * (width + height);
}
public void describe() {
System.out.println("Rectangle[width=" + width + ", height=" + height + "]");
}
@Override
public Rectangle increase_twice() {
// TODO Auto-generated method stub
return new Rectangle(2*this.width, 2*this.height);
}
}
TwoDShape.java:
public interface TwoDShape extends GeometricShape {
public double area();
}
GeometricShape.java:
public interface GeometricShape<T extends GeometricShape<T>>
{
public void describe();
public T increase_twice();
}
最后测试类ArrayListExample.java
import java.util.ArrayList;
public class ArrayListExample {
public static void describe_all(ArrayList<? extends GeometricShape> shapes)
{
for(int i=0;i<shapes.size();i++)
{
shapes.get(i).describe();
}
System.out.println("Total number of shapes:"+ shapes.size());
}
private static ArrayList<Rectangle> increase_size(ArrayList<Rectangle> rects)
{
for(int i=0;i<rects.size();i++)
{
rects.get(i).increase_twice();
}
return rects;
}
public static void main(String[] args) {
System.out.println("The result of describe() method:");
System.out.println();
System.out.println("Example rectangles");
ArrayList<Rectangle> rects = new ArrayList<Rectangle>();
rects.add(new Rectangle(2.0, 3.0));
rects.add(new Rectangle(5.0, 5.0));
describe_all(rects);
System.out.println();
System.out.println("The result of increase_twice() method:");
System.out.println();
System.out.println("Example rectangles after increase:");
ArrayList<Rectangle> double_rects = increase_size(rects);
describe_all(double_rects);
}
}
我预计增加矩形会返回矩形[宽度= 4.0,高度= 6.0] 矩形[宽度= 10.0,高度= 10.0],但它返回相同的描述方法是: Rectangle [width = 2.0,height = 3.0] Rectangle [width = 5.0,height = 5.0] 如果可能,你能告诉我我在哪里犯了一个错误吗?
非常感谢你@Yan,是的,我的理解是 –
太棒了。快乐编码! – Yan