简单java类开发一般原则：
- 类名称必须有意义，再怎么说，要让人家看的明白吧
- 类之中所有属性必须使用private封装，并提供setter,getter方法
- 类之中可以有多个构造方法，但是必须保留有一个无参数构造方法
- 类之中不允许出现任何输出语句，所有输出必须交给被调用处
- 类之中需要有一个可以取得对象完整信息的方法，一般叫做getInfo(),返回String型数据
class Book {
private String name;
private int price;
private int num;
public Book() {
}
public Book(String na ,int pri, int n) {
name = na;
price = pri;
num = n;
}
public book() {
}
public void setName(String n) {
name = n;
}
public void setPrice(int p) {
price = p;
}
public void setNum(int n) {
num = n;
}
public String getName() {
return name;
}
public int getPrice() {
return price;
}
public int getNum() {
return num;
}
public int getMonney(int price, int num) {
return price*num;
}
public String getinfo() {
return "书名:"+name+"\n"+
"单价:"+price+"\n"+
"数量:"+num+"\n";
}
}
public class test2 {
public static void main(String args[]) {
Book monney = new Book("老人与海",,);
System.out.println(monney.getinfo());
}
}一对多关系：
实例1：
省份:
省份ID : NUMBER <pk>
省份名字： VARCHAR(50)
城市：
城市ID : NUMBER<pk>
省份ID:NUMBER<fk>
城市名称:VARCHAR(50)
要求可以通过一个省份找到所有的城市信息，通过一个城市可以找到它对应的省份信息
//setter,getter,无参构造省略
class Province {
private int pid;
private String pname;
private City city [];
public Province(int pid, String pname) {
this.pid = pid;
this.pname = pname;
}
public String getInfo() {
return "省份ID:"+this.pid+"\n"+
"省份名字"+this.pname;
} public void setCity(City city []) {
this.city = city;
}
public City [] getCity() {
return this.city;
} } class City {
private int cid;
private String cname;
private Province province;
public City(int cid, String cname) {
this.cid = cid;
this.cname = cname;
}
public String getInfo() {
return "城市ID:"+ this.cid+"城市名字:"+this.cname;
}
public void setProvince(Province province) {
this.province = province;
}
public Province getProvince() {
return this.province;
}
} public class test1 {
public static void main(String args[]) {
//设置独立对象
Province p = new Province(1,"重庆");
City c_1 = new City(001,"渝中区");
City c_2 = new City(002,"南岸区");
//设置相关关系
c_1.setProvince(p);//一个城市属于一个省份
c_2.setProvince(p);
p.setCity(new City [] {c_1,c_2});
//获取数据
for (int x=0 ;x<p.getCity().length;x++) {
System.out.println(p.getCity()[x].getInfo());
}
System.out.println(c_1.getProvince().getInfo());
System.out.println(c_2.getProvince().getInfo()); }
}
//输出
城市ID:1城市名字:渝中区
城市ID:2城市名字:南岸区
省份ID:1
省份名字重庆
省份ID:1
省份名字重庆
实例2：
//setter,getter,无参构造省略
class Item {
private int iid;
private String iname;
private String note;
private Subitem subitem []; public Item(int iid, String iname,String note) {
this.iid = iid;
this.iname = iname;
this.note = note;
}
public String getInfo() {
return "类型ID:"+this.iid+"\n"+
"类型名字"+this.iname+"\n"+
"描述"+this.note;
} public void setSubitem (Subitem subitem []) {
this.subitem = subitem;
}
public Subitem [] getSubitem() {
return this.subitem;
}
} class Subitem {
private int subid;
private String subname;
private String note;
private Item item;
private Product product []; public Subitem(int subid, String subname,String note) {
this.subid = subid;
this.subname = subname;
this.note = note;
}
public String getInfo() {
return "子类型ID:" +this.subid+"\n"+
"子类型名字:"+this.subname+"\n"+
"描述"+this.note;
}
public void setItem(Item item) {
this.item = item;
}
public Item getItem() {
return this.item;
}
public void setProduct(Product product []) {
this.product = product;
}
public Product [] getProduct() {
return this.product;
}
} class Product {
private int pid;
private String pname;
private int price;
private Subitem subitem; public Product(int pid, String pname, int price) {
this.pid = pid;
this.pname = pname;
this.price = price;
}
public String getInfo() {
return "商品ID"+this.pid+"\n"+
"商品名称"+this.pname+"\n"+
"价格"+this.price;
}
public void setSubitem(Subitem subitem) {
this.subitem = subitem;
}
public Subitem getSubitem() {
return this.subitem;
}
}
public class test1 {
public static void main(String args[]) {
//设置独立对象
Item i = new Item(,"食品类","吃的"); Subitem sub1 = new Subitem(,"肉类","猪肉");
Subitem sub2= new Subitem(,"蔬菜类","白菜");
Subitem sub3 = new Subitem(,"坚果类","瓜子"); Product p1 = new Product(,"肥肉",);
Product p2= new Product(,"大白菜",);
Product p3 = new Product(,"甜瓜子",); //设置相关关系
sub1.setItem(i);//一个城市属于一个省份
sub2.setItem(i);
sub3.setItem(i);
i.setSubitem(new Subitem [] {sub1,sub2,sub3});
sub1.setProduct(new Product [] {p1});
sub2.setProduct(new Product [] {p2});
sub3.setProduct(new Product [] {p3}); p1.setSubitem(sub1);
p2.setSubitem(sub2);
p3.setSubitem(sub3);
//获取数据
for (int x= ;x<i.getSubitem().length;x++) {
System.out.println(i.getSubitem()[x].getInfo());
}
System.out.println(p3.getSubitem().getItem().getInfo());
}
}