如果要保持插入顺序，可以使用linkedhashmap：
box.java文件：

import java.util.LinkedHashMap;
import java.util.Map;

public class Box {
    private final Map<String, Integer> items;

    public Box() {
        this.items = new LinkedHashMap<>();
    }

    public void addItem(String name, int quantity) {
        this.items.put(name, this.items.getOrDefault(name, 0) + quantity);
    }

    public void viewAllItems() {
        for (Map.Entry<String, Integer> entry : this.items.entrySet()) {
            System.out.printf("%s (%d)%n", entry.getKey(), entry.getValue());
        }
    }
}

main.java文件：

public class Main {
    public static void main(String[] args) {
        Box box = new Box();
        box.addItem("shoes", 1);
        box.addItem("shoes", 3);
        box.addItem("jacket", 2);
        box.viewAllItems();
    }
}

输出：

shoes (4)
jacket (2)