1 package ex8;
 2
 3 import java.util.List;
 4
 5 public class SongDao {
 6
 7     private List<Song> songList;
 8
 9     public SongDao() {
10
11     }
12
13     public SongDao(List<Song> songList) {
14         super();
15         this.songList = songList;
16     }
17
18 //    新增歌曲
19     public void add(Song song) {
20         songList.add(song);
21     }
22
23 //    查询歌曲
24 //    按id查找
25     public Song search(int sid) {
26         for(Song song : songList) {
27             if(song.getSid()==sid){
28                 return song;
29             }
30         }
31         return null;
32     }
33 //    按对象查找
34     public Song search(Song song) {
35         if(song==null) {
36             return null;
37         }
38         return search(song.getSid());
39     }
40
41 //    删除歌曲
42 //按id删除歌曲
43     public void delete(int sid) {
44         Song song=search(sid);
45         if(song!=null) {
46             songList.remove(song);
47         }
48     }
49 //按对象删除歌曲
50     public void delete(Song song) {
51         if(song!=null) {
52             delete(song.getSid());
53         }
54     }
55
56     public List<Song> getSongList() {
57         return songList;
58     }
59
60     public void setSongList(List<Song> songList) {
61         this.songList = songList;
62     }
63
64
65
66
67 }

package ex4_1;public class Rectangle extends Shape {private double width;private double height;public Rectangle(double height,double width) {super();// TODO Auto-generated constructor stub
        setHeight(height);setWidth(width);}@Overridepublic double length() {// TODO Auto-generated method stubreturn 2*(width+height);}@Overridepublic double area() {// TODO Auto-generated method stubreturn width*height;}public double differ() {return Math.abs(height-width);}public double getWidth() {return width;}public void setWidth(double width) {this.width = width;}public double getHeight() {return height;}public void setHeight(double height) {this.height = height;}}

package ex4_1;public class Shape {public double length(){return 0;}public double area() {return 0;}
}

 1 package ex4_1;
 2
 3 public class Square extends Rectangle {
 4
 5     public double edge;
 6
 7     public Square(double edge) {
 8         super(edge,edge);
 9         setEdge(edge);
10         // TODO Auto-generated constructor stub
11     }
12
13     public double getEdge() {
14         return edge;
15     }
16
17     public void setEdge(double edge) {
18         this.edge = edge;
19     }
20
21
22 }

package ex4_1;public class Tester {public static void main (String[] args) {Shape[] shapes= {new Rectangle(5,10),new circle(5),new Square(3),new Triangle(3, 4, 5)};for(int i=0;i<shapes.length;i++) {double length=shapes[i].length();double area=shapes[i].area();if(shapes[i]instanceof circle) {System.out.println("Shape("+(i+1)+")"+"length"+String.format("%.2f", length)+",area"+String.format("%.2f", area));}else {System.out.println("Shape("+(i+1)+")"+"length"+length+",area"+area);if(shapes[i]instanceof Rectangle) {Rectangle r=(Rectangle)shapes[i];System.out.println("长宽差是"+r.differ());}}}}
}

package ex4_1;public class Triangle extends Shape {private double a;private double b;private double c;public Triangle(double a,double b,double c) {super();// TODO Auto-generated constructor stub
        setA(a);setB(b);setC(c);}@Overridepublic double length() {// TODO Auto-generated method stubreturn a+b+c;}@Overridepublic double area() {double p= (a+b+c)/2;// TODO Auto-generated method stubreturn Math.sqrt(p*(p-a)*(p-b)*(p-c));}public double getA() {return a;}public void setA(double a) {this.a = a;}public double getB() {return b;}public void setB(double b) {this.b = b;}public double getC() {return c;}public void setC(double c) {this.c = c;}
}