[英]implementing Comparable interface from abstract class with concrete subclasses
[英]Error extending from an abstract class and implementing the Comparable interface
尽管GeometricObject没有错误,但是GeoCircle会显示一个错误,说明GeoCircle不是抽象的,并且尽管compareTo方法未编写为抽象类//实现可比较接口的抽象类GeometricObject,但它并未覆盖抽象方法compareTo(GeometricObject)
public abstract class GeometricObject implements Comparable<GeometricObject>
{
public String name;
//sample abstract class of getting area of various shapes
public abstract double getArea();
//sample abstract class for getting perimeter/circumference of various shapes
public abstract double getPerimeter();
//pass in and return name of the object selected in a system out line
public void name(String n)
{
System.out.println("This is a " + n);
}
/** A method for comparing the areas of two geometric objects and returning a boolean for their equals */
public static boolean equalArea(GeometricObject object1,GeometricObject object2)
{
//comparing double to another double
return object1.getArea()==object2.getArea();
}
// a method to find the bigger between two GeometricObjects and returning a String statement
public static void max(GeometricObject g1, GeometricObject g2)
{
if(g1.compareTo(g2)>0)
System.out.println("Object 1 is larger ");
else if (g1.compareTo(g2)<0)
System.out.println("Object 2 is larger ");
else
System.out.println("Objects are the same ");
}
// an override of the compareTo method from the implemented comparable interface
public int compareTo(GeometricObject g1, GeometricObject g2)
{
if(g1.getArea()>g2.getArea())
return 1;
else if (g1.getArea()<g2.getArea())
return -1;
else
return 0;
}
}
//a class for calculating circumference and area of a circle extended from GeometricObject
public class GeoCircle extends GeometricObject implements Comparable<GeoCircle>
{
public String name;
public double radius;
//constructor for only inputting radius of the circle
public GeoCircle(double r)
{
radius = r;
}
// 2ndconstructor taking a name for the shape and radius of the circle
public GeoCircle(String n, double r)
{
name = n;
radius = r;
}
//method to get area of the shape with previously passed in radius
public double getArea()
{
return Math.PI*Math.pow(radius,2);
}
//method to get circumference of the circle with radius previously given
public double getPerimeter()
{
return 2*Math.PI*radius;
}
//a compareTo method
public int compareTo(GeoCircle obj)
{
if (this.getArea() > obj.getArea())
return 1;
else if (this.getArea() < obj.getArea())
return -1;
else
return 0;
}
}
public int compareTo(GeometricObject g1, GeometricObject g2)
{
if(g1.getArea()>g2.getArea())
return 1;
else if (g1.getArea()<g2.getArea())
return -1;
else
return 0;
}
没有正确覆盖compareTo
。 compareTo
应该采用一个参数并将this
与该参数进行比较。 这可以实现为
@Override public int compareTo(GeometricObject g) {
return Double.compare(getArea(), g.getArea());
}
作为参考,添加@Override注释可验证方法是否正确覆盖了将被捕获的超类方法。
您应该在基类中使用泛型:
public abstract class GeometricObject<T extends GeometricObject> implements Comparable<T> {
...
// an override of the compareTo method from the implemented comparable interface
public int compareTo(T that) {
if(this.getArea()>that.getArea())
return 1;
else if (this.getArea()<that.getArea())
return -1;
else
return 0;
}
}
//a class for calculating circumference and area of a circle extended from GeometricObject
public class GeoCircle extends GeometricObject<GeoCircle> {
...
@Override // Remove this method if it doesn't differ from parent implementation
public int compareTo(GeoCircle that) {
...
}
}
可比的接口非常严格。 更好的解决方案是实现单独的比较器并从基类中删除Comparable声明:
class GeometricObjectAreaComparator implements Comparator<GeometricObject> {
@Override
public int compare(GeometricObject o1, GeometricObject o2) {
...
}
}
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