JAVA基础学习之路（四）定义简单java类

简单java类开发一般原则：

1. 类名称必须有意义，再怎么说，要让人家看的明白吧
2. 类之中所有属性必须使用private封装，并提供setter,getter方法
3. 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
4. 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
5. 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+"
"+
               "单价:"+price+"
"+
               "数量:"+num+"
";
    }
}

public class test2 {
    public static void main(String args[]) {
        Book monney = new Book("老人与海",20,3);
        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+"
"+
                "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+"
"+
                "类型名字"+this.iname+"
"+
                "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+"
"+
                "子类型名字:"+this.subname+"
"+
                "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+"
"+
                "商品名称"+this.pname+"
"+
                "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(1,"食品类","吃的");
        
        Subitem sub1 = new Subitem(001,"肉类","猪肉");
        Subitem sub2= new Subitem(002,"蔬菜类","白菜");
        Subitem sub3 = new Subitem(003,"坚果类","瓜子");
        
        Product p1 = new Product(0001,"肥肉",20);
        Product p2= new Product(0002,"大白菜",5);
        Product p3 = new Product(0003,"甜瓜子",12);
        
        //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=0 ;x<i.getSubitem().length;x++) {
            System.out.println(i.getSubitem()[x].getInfo());
        }
        System.out.println(p3.getSubitem().getItem().getInfo());
    }    
}