用java编写。1建个商品类，属性有商品编号、商品名称、商品价格、商品数量 2将商品放入集合中 3执行程序时，有3个功能让用户选择，添加商品、删除商品、显示已有商品。删除商品时需判断商品是否存在(可通过商品编号或者商品名称判断)，这三个功能均写成方法。用户选择退出时才能退出。

以下是Java代码实现：

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Scanner;

public class GoodsManagement {
    private static List<Goods> goodsList = new ArrayList<>(); // 商品集合

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int choice = 0;
        while (choice != 4) {
            System.out.println("1.添加商品");
            System.out.println("2.删除商品");
            System.out.println("3.显示已有商品");
            System.out.println("4.退出");
            System.out.print("请输入您的选择：");
            choice = sc.nextInt();
            switch (choice) {
                case 1:
                    addGoods();
                    break;
                case 2:
                    deleteGoods();
                    break;
                case 3:
                    showGoods();
                    break;
                case 4:
                    System.out.println("谢谢使用！");
                    break;
                default:
                    System.out.println("输入错误，请重新输入！");
            }
        }
    }

    // 添加商品
    public static void addGoods() {
        Scanner sc = new Scanner(System.in);
        System.out.print("请输入商品编号：");
        int id = sc.nextInt();
        System.out.print("请输入商品名称：");
        String name = sc.next();
        System.out.print("请输入商品价格：");
        double price = sc.nextDouble();
        System.out.print("请输入商品数量：");
        int quantity = sc.nextInt();
        Goods goods = new Goods(id, name, price, quantity);
        goodsList.add(goods);
        System.out.println("商品添加成功！");
    }

    // 删除商品
    public static void deleteGoods() {
        Scanner sc = new Scanner(System.in);
        System.out.println("请选择删除方式：");
        System.out.println("1.按商品编号删除");
        System.out.println("2.按商品名称删除");
        System.out.print("请输入您的选择：");
        int choice = sc.nextInt();
        if (choice == 1) {
            System.out.print("请输入商品编号：");
            int id = sc.nextInt();
            boolean flag = false;
            Iterator<Goods> it = goodsList.iterator();
            while (it.hasNext()) {
                Goods goods = it.next();
                if (goods.getId() == id) {
                    it.remove();
                    flag = true;
                    System.out.println("商品删除成功！");
                    break;
                }
            }
            if (!flag) {
                System.out.println("商品不存在！");
            }
        } else if (choice == 2) {
            System.out.print("请输入商品名称：");
            String name = sc.next();
            boolean flag = false;
            Iterator<Goods> it = goodsList.iterator();
            while (it.hasNext()) {
                Goods goods = it.next();
                if (goods.getName().equals(name)) {
                    it.remove();
                    flag = true;
                    System.out.println("商品删除成功！");
                    break;
                }
            }
            if (!flag) {
                System.out.println("商品不存在！");
            }
        } else {
            System.out.println("输入错误，请重新选择！");
        }
    }

    // 显示商品
    public static void showGoods() {
        System.out.println("商品编号\t商品名称\t商品价格\t商品数量");
        for (Goods goods : goodsList) {
            System.out.println(goods.getId() + "\t\t" + goods.getName() + "\t\t" + goods.getPrice() + "\t\t" + goods.getQuantity());
        }
    }
}

class Goods {
    private int id; // 商品编号
    private String name; // 商品名称
    private double price; // 商品价格
    private int quantity; // 商品数量

    public Goods(int id, String name, double price, int quantity) {
        this.id = id;
        this.name = name;
        this.price = price;
        this.quantity = quantity;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public int getQuantity() {
        return quantity;
    }

    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }
}

使用时，直接运行 `GoodsManagement` 类即可。