某单据管理系统中要求实现对采购、销售、库存的单据管理，系统的采购类的单据中有如采购单、收货单、应付帐单、付款单和退货单等，现使用抽象工厂方法设计模式设计该系统，绘制类图并编程实现。 实验分析：单据的本质就是资金的“收入”与“支出”，所以分为收入与支出两个工厂来生产单据。 采购(Purchase)：采购单（支出）、退货单（收入） 销售（Sale）：退款单（支出）、销售单（收入） 库存(Stock)：入库单（支出）、出库单（收入）

以下是该系统的抽象工厂方法设计模式的类图：


具体实现如下：

// 抽象工厂
interface BillFactory {
    PurchaseBill createPurchaseBill();
    SaleBill createSaleBill();
    StockBill createStockBill();
}

// 支出工厂
class ExpenseFactory implements BillFactory {
    public PurchaseBill createPurchaseBill() {
        return new PurchaseBill();
    }
    public SaleBill createSaleBill() {
        return new RefundBill();
    }
    public StockBill createStockBill() {
        return new InStockBill();
    }
}

// 收入工厂
class IncomeFactory implements BillFactory {
    public PurchaseBill createPurchaseBill() {
        return new RefundBill();
    }
    public SaleBill createSaleBill() {
        return new SaleBill();
    }
    public StockBill createStockBill() {
        return new OutStockBill();
    }
}

// 抽象单据类
abstract class Bill {
    protected String id;
    protected Date date;
    protected double amount;

    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public Date getDate() {
        return date;
    }
    public void setDate(Date date) {
        this.date = date;
    }
    public double getAmount() {
        return amount;
    }
    public void setAmount(double amount) {
        this.amount = amount;
    }

    public abstract void printBill();
}

// 采购类单据
abstract class PurchaseBill extends Bill {}

class PurchaseOrderBill extends PurchaseBill {
    public void printBill() {
        System.out.println("采购单：id=" + id + ", date=" + date + ", amount=" + amount);
    }
}

class PurchaseReceiptBill extends PurchaseBill {
    public void printBill() {
        System.out.println("收货单：id=" + id + ", date=" + date + ", amount=" + amount);
    }
}

class PayableBill extends PurchaseBill {
    public void printBill() {
        System.out.println("应付帐单：id=" + id + ", date=" + date + ", amount=" + amount);
    }
}

class PaymentBill extends PurchaseBill {
    public void printBill() {
        System.out.println("付款单：id=" + id + ", date=" + date + ", amount=" + amount);
    }
}

class PurchaseReturnBill extends PurchaseBill {
    public void printBill() {
        System.out.println("退货单：id=" + id + ", date=" + date + ", amount=" + amount);
    }
}

// 销售类单据
abstract class SaleBill extends Bill {}

class RefundBill extends SaleBill {
    public void printBill() {
        System.out.println("退款单：id=" + id + ", date=" + date + ", amount=" + amount);
    }
}

class SalesBill extends SaleBill {
    public void printBill() {
        System.out.println("销售单：id=" + id + ", date=" + date + ", amount=" + amount);
    }
}

// 库存类单据
abstract class StockBill extends Bill {}

class InStockBill extends StockBill {
    public void printBill() {
        System.out.println("入库单：id=" + id + ", date=" + date + ", amount=" + amount);
    }
}

class OutStockBill extends StockBill {
    public void printBill() {
        System.out.println("出库单：id=" + id + ", date=" + date + ", amount=" + amount);
    }
}

// 测试
public class Test {
    public static void main(String[] args) {
        // 支出工厂
        BillFactory expenseFactory = new ExpenseFactory();
        PurchaseBill purchaseOrderBill = expenseFactory.createPurchaseBill();
        purchaseOrderBill.setId("PO0001");
        purchaseOrderBill.setDate(new Date());
        purchaseOrderBill.setAmount(1000);
        purchaseOrderBill.printBill();

        SaleBill refundBill = expenseFactory.createSaleBill();
        refundBill.setId("R0001");
        refundBill.setDate(new Date());
        refundBill.setAmount(500);
        refundBill.printBill();

        StockBill inStockBill = expenseFactory.createStockBill();
        inStockBill.setId("IS0001");
        inStockBill.setDate(new Date());
        inStockBill.setAmount(800);
        inStockBill.printBill();

        // 收入工厂
        BillFactory incomeFactory = new IncomeFactory();
        PurchaseBill purchaseReturnBill = incomeFactory.createPurchaseBill();
        purchaseReturnBill.setId("PR0001");
        purchaseReturnBill.setDate(new Date());
        purchaseReturnBill.setAmount(200);
        purchaseReturnBill.printBill();

        SaleBill salesBill = incomeFactory.createSaleBill();
        salesBill.setId("S0001");
        salesBill.setDate(new Date());
        salesBill.setAmount(3000);
        salesBill.printBill();

        StockBill outStockBill = incomeFactory.createStockBill();
        outStockBill.setId("OS0001");
        outStockBill.setDate(new Date());
        outStockBill.setAmount(500);
        outStockBill.printBill();
    }
}