JAVA基礎學習之路（四）定義簡單java類

簡單java類開發一般原則：

1. 類名稱必須有意義，再怎么說，要讓人家看的明白吧
2. 類之中所有屬性必須使用private封裝，並提供setter,getter方法
3. 類之中可以有多個構造方法，但是必須保留有一個無參數構造方法
4. 類之中不允許出現任何輸出語句，所有輸出必須交給被調用處
5. 類之中需要有一個可以取得對象完整信息的方法，一般叫做getInfo(),返回String型數據

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 "書名:"+name+"\n"+
               "單價:"+price+"\n"+
               "數量:"+num+"\n";
    }
}

public class test2 {
    public static void main(String args[]) {
        Book monney = new Book("老人與海",20,3);
        System.out.println(monney.getinfo());
    }
}

 

 

一對多關系：

實例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>

城市名稱:VARCHAR(50)

要求可以通過一個省份找到所有的城市信息，通過一個城市可以找到它對應的省份信息

//setter,getter,無參構造省略
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[]) {
        //設置獨立對象
        Province p = new Province(1,"重慶");
        City c_1 = new City(001,"渝中區");
        City c_2 = new City(002,"南岸區");
        //設置相關關系
        c_1.setProvince(p);//一個城市屬於一個省份
        c_2.setProvince(p);
        p.setCity(new City [] {c_1,c_2});
        //獲取數據
        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());
    
    }    
}
//輸出
城市ID:1城市名字:渝中區
城市ID:2城市名字:南岸區
省份ID:1
省份名字重慶
省份ID:1
省份名字重慶

 

實例2：

 

//setter,getter,無參構造省略
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 "類型ID:"+this.iid+"\n"+
                "類型名字"+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 "子類型ID:" +this.subid+"\n"+
                "子類型名字:"+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"+
                "商品名稱"+this.pname+"\n"+
                "價格"+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[]) {
        //設置獨立對象
        Item i = new Item(1,"食品類","吃的");
        
        Subitem sub1 = new Subitem(001,"肉類","豬肉");
        Subitem sub2= new Subitem(002,"蔬菜類","白菜");
        Subitem sub3 = new Subitem(003,"堅果類","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);
        
        //設置相關關系
        sub1.setItem(i);//一個城市屬於一個省份
        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);
        //獲取數據
        for (int x=0 ;x<i.getSubitem().length;x++) {
            System.out.println(i.getSubitem()[x].getInfo());
        }
        System.out.println(p3.getSubitem().getItem().getInfo());
    }    
}