今天要學的是 Sorted Collections
StockItem.java
package Stock;public class StockItem implements Comparable<StockItem> {
private final String name;
private double price;
private int quantityStock = 0; public StockItem(String name, double price) {
this.name = name;
this.price = price;
this.quantityStock = 0; // or here ( but you wouldn't normally do both)
} public StockItem(String name, double price, int quantityStock) {
this.name = name;
this.price = price;
this.quantityStock = quantityStock;
} public String getName() {
return name;
} public double getPrice() {
return price;
} public void setPrice(double price) {
if (price > 0.0) {
this.price = price;
}
} public int quantityInStock() {
return quantityStock;
} public void adjustStock(int quantity) {
int newQuantity = this.quantityStock + quantity;
if (newQuantity >= 0) {
this.quantityStock = newQuantity;
}
} @Override
public int hashCode() {
return this.name.hashCode() + 17;
} @Override
public boolean equals(Object obj) {
System.out.println("Call Stock.StockItem.equals()");
if (obj == this) {
return true;
} if ((obj == null) || (obj.getClass() != this.getClass())) {
return false;
} String objName = ((StockItem) obj).getName();
return this.name.equals(objName);
} @Override
public int compareTo(StockItem o) {
System.out.println("Call Stock.StockItem.compareTo()");
if (this == o) {
return 0;
}
if (o != null) {
return this.name.compareTo(o.getName());
} throw new NullPointerException();
} @Override
public String toString() {
return name + " : $" + price;
}
}
StockList.java
package Stock;import java.util.Collections;
import java.util.HashMap;
import java.util.Map;public class StockList {
private final Map<String, StockItem> list; public StockList() {
this.list = new HashMap<>();
} public int addStock(StockItem stockItem) {
if (stockItem != null) {
// check if already have stockItem, jf get null just pass stockItem of parameter
StockItem inStock = list.getOrDefault(stockItem.getName(), stockItem);
// if there are already stocks on this item, adjust the quantity
if (inStock != stockItem) {
stockItem.adjustStock(inStock.quantityInStock());
}
list.put(stockItem.getName(), stockItem);
return stockItem.quantityInStock();
}
return 0;
} public int sellStock(String item, int quantity) {
StockItem inStock = list.getOrDefault(item, null);
if ((inStock != null) && (inStock.quantityInStock() >= quantity) && (quantity > 0)) {
inStock.adjustStock(-quantity);
return quantity;
}
return 0;
} public StockItem getStockItem(String key) {
return list.get(key);
} public Map<String, StockItem> Items() {
return Collections.unmodifiableMap(list);
} @Override
public String toString() {
String s = "\nStock List\n";
double totalCost = 0.0;
for (Map.Entry<String, StockItem> item : list.entrySet()) {
StockItem stockItem = item.getValue(); double itemValue = stockItem.getPrice() * stockItem.quantityInStock(); s = s + stockItem + " There are " + stockItem.quantityInStock() + " items in stock. Total value of items: ";
s = s + itemValue + "\n";
totalCost += itemValue;
} return s + " Total stock value " + totalCost;
}
}
Basket.java
package Stock;import java.util.Collections;
import java.util.HashMap;
import java.util.Map;public class Basket {
private final String name;
private final Map<StockItem, Integer> list; public Basket(String name) {
this.name = name;
this.list = new HashMap<>();
} public int addToBasket(StockItem item, int quantity) {
if ((item != null) && (quantity > 0)) {
int inBasket = list.getOrDefault(item, 0);
list.put(item, inBasket + quantity);
return inBasket;
}
return 0;
} public Map<StockItem, Integer> Items() {
return Collections.unmodifiableMap(list);
} @Override
public String toString() {
String s = "\nShopping basket " + name + " contains " + list.size() + " items\n";
double totalCost = 0.0;
for (Map.Entry<StockItem, Integer> item : list.entrySet()) {
s = s + item.getKey() + ". " + item.getValue() + " purchased\n";
totalCost += item.getKey().getPrice() * item.getValue();
}
return s + " Total cost " + totalCost;
}
}
Main.java
package Stock;public class Main {
private static StockList stockList = new StockList(); public static void main(String[] args) {
StockItem temp = new StockItem("bread", 0.86, 100);
stockList.addStock(temp); temp = new StockItem("cake", 1.10, 7);
stockList.addStock(temp); temp = new StockItem("car", 12.50, 2);
stockList.addStock(temp); temp = new StockItem("chair", 62.0, 10);
stockList.addStock(temp); temp = new StockItem("cup", 0.50, 200);
stockList.addStock(temp); temp = new StockItem("door", 72.95, 4);
stockList.addStock(temp); temp = new StockItem("juice", 2.50, 36);
stockList.addStock(temp); temp = new StockItem("phone", 96.99, 35);
stockList.addStock(temp); temp = new StockItem("towel", 2.40, 80);
stockList.addStock(temp); temp = new StockItem("vase", 8.76, 40);
stockList.addStock(temp); System.out.println(stockList);
}
}
輸出結果：
Stock List
door : $72.95 There are 4 items in stock. Total value of items: 291.8
bread : $0.86 There are 100 items in stock. Total value of items: 86.0
car : $12.5 There are 2 items in stock. Total value of items: 25.0
phone : $96.99 There are 35 items in stock. Total value of items: 3394.6499999999996
towel : $2.4 There are 80 items in stock. Total value of items: 192.0
cake : $1.1 There are 7 items in stock. Total value of items: 7.700000000000001
chair : $62.0 There are 10 items in stock. Total value of items: 620.0
vase : $8.76 There are 40 items in stock. Total value of items: 350.4
juice : $2.5 There are 36 items in stock. Total value of items: 90.0
cup : $0.5 There are 200 items in stock. Total value of items: 100.0
Total stock value 5157.549999999999
看起來小複雜，其實就是一個簡單的庫存清單
裡面有三個 Class，分別是商品、庫存、購物籃
還有個小問題要修改，就是數字那邊怪怪的
StockList.java 改
package Stock;import java.util.Collections;
import java.util.HashMap;
import java.util.Map;public class StockList {
private final Map<String, StockItem> list; public StockList() {
this.list = new HashMap<>();
} public int addStock(StockItem stockItem) {
if (stockItem != null) {
// check if already have stockItem, jf get null just pass stockItem of parameter
StockItem inStock = list.getOrDefault(stockItem.getName(), stockItem);
// if there are already stocks on this item, adjust the quantity
if (inStock != stockItem) {
stockItem.adjustStock(inStock.quantityInStock());
}
list.put(stockItem.getName(), stockItem);
return stockItem.quantityInStock();
}
return 0;
} public int sellStock(String item, int quantity) {
StockItem inStock = list.getOrDefault(item, null);
if ((inStock != null) && (inStock.quantityInStock() >= quantity) && (quantity > 0)) {
inStock.adjustStock(-quantity);
return quantity;
}
return 0;
} public StockItem getStockItem(String key) {
return list.get(key);
} public Map<String, StockItem> Items() {
return Collections.unmodifiableMap(list);
} @Override
public String toString() {
String s = "\nStock List\n";
double totalCost = 0.0;
for (Map.Entry<String, StockItem> item : list.entrySet()) {
StockItem stockItem = item.getValue(); double itemValue = stockItem.getPrice() * stockItem.quantityInStock(); s = s + stockItem + " There are " + stockItem.quantityInStock() + " items in stock. Total value of items: ";
s = s + String.format("%.2f", itemValue) + "\n";
totalCost += itemValue;
} return s + " Total stock value " + String.format("%.2f", totalCost);
}
}
輸出結果：
Stock List
door : $72.95 There are 4 items in stock. Total value of items: 291.80
bread : $0.86 There are 100 items in stock. Total value of items: 86.00
car : $12.5 There are 2 items in stock. Total value of items: 25.00
phone : $96.99 There are 35 items in stock. Total value of items: 3394.65
towel : $2.4 There are 80 items in stock. Total value of items: 192.00
cake : $1.1 There are 7 items in stock. Total value of items: 7.70
chair : $62.0 There are 10 items in stock. Total value of items: 620.00
vase : $8.76 There are 40 items in stock. Total value of items: 350.40
juice : $2.5 There are 36 items in stock. Total value of items: 90.00
cup : $0.5 There are 200 items in stock. Total value of items: 100.00
Total stock value 5157.55
這樣就只會顯示到小數點第二位，數字多少就是幾位
但物品的排列不是按照字母，是無序隨機的，想要有順序怎改?
StockList.java 改
package Stock;import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.Map;public class StockList {
private final Map<String, StockItem> list; public StockList() {
this.list = new LinkedHashMap<>();
} public int addStock(StockItem stockItem) {
if (stockItem != null) {
// check if already have stockItem, jf get null just pass stockItem of parameter
StockItem inStock = list.getOrDefault(stockItem.getName(), stockItem);
// if there are already stocks on this item, adjust the quantity
if (inStock != stockItem) {
stockItem.adjustStock(inStock.quantityInStock());
}
list.put(stockItem.getName(), stockItem);
return stockItem.quantityInStock();
}
return 0;
} public int sellStock(String item, int quantity) {
StockItem inStock = list.getOrDefault(item, null);
if ((inStock != null) && (inStock.quantityInStock() >= quantity) && (quantity > 0)) {
inStock.adjustStock(-quantity);
return quantity;
}
return 0;
} public StockItem getStockItem(String key) {
return list.get(key);
} public Map<String, StockItem> Items() {
return Collections.unmodifiableMap(list);
} @Override
public String toString() {
String s = "\nStock List\n";
double totalCost = 0.0;
for (Map.Entry<String, StockItem> item : list.entrySet()) {
StockItem stockItem = item.getValue(); double itemValue = stockItem.getPrice() * stockItem.quantityInStock(); s = s + stockItem + " There are " + stockItem.quantityInStock() + " items in stock. Total value of items: ";
s = s + String.format("%.2f", itemValue) + "\n";
totalCost += itemValue;
} return s + " Total stock value " + String.format("%.2f", totalCost);
}
}
輸出結果：
Stock List
bread : $0.86 There are 100 items in stock. Total value of items: 86.00
cake : $1.1 There are 7 items in stock. Total value of items: 7.70
car : $12.5 There are 2 items in stock. Total value of items: 25.00
chair : $62.0 There are 10 items in stock. Total value of items: 620.00
cup : $0.5 There are 200 items in stock. Total value of items: 100.00
door : $72.95 There are 4 items in stock. Total value of items: 291.80
juice : $2.5 There are 36 items in stock. Total value of items: 90.00
phone : $96.99 There are 35 items in stock. Total value of items: 3394.65
towel : $2.4 There are 80 items in stock. Total value of items: 192.00
vase : $8.76 There are 40 items in stock. Total value of items: 350.40
Total stock value 5157.55
只需要改一行而已非常方便
public StockList() {
this.list = new LinkedHashMap<>();
}