从具有子类的抽象类实现Comparable接口
package geometricobject; public abstract class GeometricObject implements Comparable { private String color = "white"; private boolean filled; private java.util.Date dateCreated; protected GeometricObject(){ dateCreated = new java.util.Date(); } protected GeometricObject(String color, boolean filled){ dateCreated = new java.util.Date(); this.color = color; this.filled = filled; } public String getColor(){ return color; } public void setColor(String color){ this.color = color; } public boolean isFilled(){ return filled; } public void setFilled(boolean filled){ this.filled = filled; } public java.util.Date getDateCreated() { return dateCreated; } public String toString() { return "Created on " + dateCreated + "\ncolor: " + color + "and filled: " + filled; } public static void main(String[] args) { GeometricObject circle1 = new Circle(1, "Red", true); GeometricObject circle2 = new Circle(2, "Blue", false); GeometricObject maxCircle = new Circle(); GeometricObject rect1 = new Rectangle(1, 1, "Red", true); GeometricObject rect2 = new Rectangle(2, 2, "Blue", false); GeometricObject maxRect = new Rectangle(); maxCircle = GeometricObject.max(circle1, circle2); maxRect = GeometricObject.max(rect1, rect2); System.out.println(maxCircle.toString()); System.out.println(maxRect.toString()); } public static GeometricObject max (GeometricObject o1, GeometricObject o2){ if (((Comparable)o1).compareTo(o2) > 0 ) return o1; else return o2; } public interface Comparable { public int compareTo(GeometricObject o); } public int compareTo(GeometricObject o) { if (this.getArea() > o.getArea()) return 1; else if (this.getArea() < o.getArea()) return -1; else return 0; } public abstract double getArea(); } CIRCLE类
class Circle extends GeometricObject { private double radius; public Circle() { } public Circle(double radius){ this.radius = radius; } public Circle(double radius, String color, boolean filled){ this.radius = radius; setColor(color); setFilled(filled); } public double getRadius(){ return radius; } public void setRadius(double radius){ this.radius = radius; } public double getArea(){ return radius * radius * Math.PI; } public double getDiameter(){ return 2 * radius; } public double getPerimeter(){ return 2 * radius * Math.PI; } public void printCircle() { System.out.println("The circle is created " + getDateCreated() + " and the radius is " + radius); } }
矩形类
class Rectangle extends GeometricObject { private double width; private double height; public Rectangle() { } public Rectangle(double Width, double Height){ this.width = Width; this.height = Height; } public Rectangle(double Width, double Height, String Color, boolean Filled){ this.width = Width; this.height = Height; setColor(Color); setFilled(Filled); } public double getWidth(){ return width; } public double getHeight(){ return height; } public void setHeight(double Height){ this.height = Height; } public double getArea(){ return width * height; } public double getPerimeter(){ return 2 * (width + height); } }
所以我试图做这个单独的类并不断得到这个错误。
Exception in thread "main" java.lang.ExceptionInInitializerError at geometricobject.GeometricObject.main(GeometricObject.java:44) Caused by: java.lang.RuntimeException: Uncompilable source code - geometricobject.Circle is not abstract and does not override abstract method compareTo(java.lang.Object) in java.lang.Comparable at geometricobject.Circle.(Circle.java:12) ... 1 more Java Result: 1
改变线
public abstract class GeometricObject implements Comparable {
至
public abstract class GeometricObject implements Comparable {
没有generics，你需要实现的方法是compareTo(Object) ，而不是compareTo(GeometricObject)
在实现或覆盖某些方法时，始终可以使用@Override注释。
public abstract class GeometricObject implements java.lang.Comparable { @Override public int compareTo(GeometricObject o) { int result = 0; //do comparision return result; } }