# Vending Machine

**Description**

* The Vending Machine has three states：`NoSelection`, `HasSelection`, `InsertedMoney`
* The Vending Machine sells three drink：`Coke`, `Sprite` and `MountainDew`
* The Vending Machine should print the correct information in correct state

### Example

```
select("Coke")
select("Sprite")
insert(500)
execTrans()
```

You should return below:

```
Current selection is: Coke, current inserted money: 0, current state is : HasSelection
Current selection is: Sprite, current inserted money: 0, current state is : HasSelection
Current selection is: Sprite, current inserted money: 500, current state is : InsertedMoney
Current selection is: null, current inserted money: 0, current state is : NoSelection
```

## Solution

```java
/**
* This reference program is provided by @jiuzhang.com
* Copyright is reserved. Please indicate the source for forwarding
*/

public class VendingMachine {
    private String currentSelectedItem;
    private int currentInsertedMoney;
    private AbstractState state;
    private NoSelectionState noSelectionState;
    private HasSelectionState hasSelectionState;
    private InsertedMoneyState insertedMoneyState;
    private Map<String, Integer> itemPrice;

    public VendingMachine() {
        currentInsertedMoney = 0;
        currentSelectedItem = null;
        noSelectionState = new NoSelectionState(this);
        hasSelectionState = new HasSelectionState(this);
        insertedMoneyState = new InsertedMoneyState(this);
        state = noSelectionState;

        itemPrice = new HashMap<>();
        itemPrice.put("Coke", 199);
        itemPrice.put("Sprite", 299);
        itemPrice.put("MountainDew", 399);
    }

    public void setSelectedItem(String item) {
        this.currentSelectedItem = item;
    }

    public String getSelectedItem() {
        return currentSelectedItem;
    }

    public void insertMoney(int amount) {
        this.currentInsertedMoney += amount;
    }

    public void emptyInsertedMoney() {
        this.currentInsertedMoney = 0;
    }

    public int getInsertedMoney() {
        return currentInsertedMoney;
    }

    public int getSalePrice() {
        if (currentSelectedItem == null) {
            System.out.println("Please make a selection before asking price");
            return 0;
        } else {
            return itemPrice.get(currentSelectedItem);
        }
    }

    public void changeToNoSelectionState() {
        state = noSelectionState;
    }

    public void changeToHasSelectionState() {
        state = hasSelectionState;
    }

    public void changeToInsertedMoneyState() {
        state = insertedMoneyState;
    }

    public void selectItem(String selection) {
        state.selectItem(selection);
    }

    public void addMoney(int value) {
        state.insertMoney(value);
    }

    public void executeTransaction() {
        state.executeTransaction();
    }

    public int cancelTransaction() {
        return state.cancelTransaction();
    }

    public String printState() {
        String res = "";

        res = "Current selection is: " + currentSelectedItem + ", current inserted money: " + currentInsertedMoney
                + ", current state is : " + state;

        return res;
    }
}

interface State {
    public void selectItem(String selection);
    public void insertMoney(int value);
    public void executeTransaction();
    public int cancelTransaction();
    public String toString();
}

abstract class AbstractState implements State {
    protected VendingMachine vendingMachine;

    public AbstractState(VendingMachine vendingMachine) {
        this.vendingMachine = vendingMachine;
    }
}

class NoSelectionState extends AbstractState{

    public NoSelectionState(VendingMachine vendingMachine) {
        super(vendingMachine);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void selectItem(String selection) {
        // TODO Auto-generated method stub
        vendingMachine.setSelectedItem(selection);
        vendingMachine.changeToHasSelectionState();
    }

    @Override
    public void insertMoney(int value) {
        // TODO Auto-generated method stub
        System.out.println("Please make a selection first");
    }

    @Override
    public void executeTransaction() {
        // TODO Auto-generated method stub
        System.out.println("Please make a selection first");
    }

    @Override
    public int cancelTransaction() {
        // TODO Auto-generated method stub
        System.out.println("Please make a selection first");
        return 0;
    }

    @Override
    public String toString(){
        return "NoSelection";
    }
}

class HasSelectionState extends AbstractState{

    public HasSelectionState(VendingMachine vendingMachine) {
        super(vendingMachine);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void selectItem(String selection) {
        // TODO Auto-generated method stub
        vendingMachine.setSelectedItem(selection);
    }

    @Override
    public void insertMoney(int value) {
        // TODO Auto-generated method stub
        vendingMachine.insertMoney(value);
        vendingMachine.changeToInsertedMoneyState();
    }

    @Override
    public void executeTransaction() {
        // TODO Auto-generated method stub
        System.out.println("You need to insert money first");
    }

    @Override
    public int cancelTransaction() {
        // TODO Auto-generated method stub
        System.out.println("Transaction canceled");
        vendingMachine.setSelectedItem(null);
        vendingMachine.changeToNoSelectionState();
        return 0;
    }
    @Override
    public String toString(){
        return "HasSelection";
    }
}

class InsertedMoneyState extends AbstractState{

    public InsertedMoneyState(VendingMachine vendingMachine) {
        super(vendingMachine);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void selectItem(String selection) {
        // TODO Auto-generated method stub
        System.out.println("Already has a selection, please cancel transaction to make a new selection");
    }

    @Override
    public void insertMoney(int value) {
        // TODO Auto-generated method stub
        vendingMachine.insertMoney(value);
    }

    @Override
    public void executeTransaction() {
        // TODO Auto-generated method stub
        int diff = vendingMachine.getInsertedMoney() - vendingMachine.getSalePrice();
        if(diff >= 0){
            System.out.println("Executing transaction, will return you : " + diff + " money and item: " + vendingMachine.getSelectedItem());
            vendingMachine.setSelectedItem(null);
            vendingMachine.emptyInsertedMoney();
            vendingMachine.changeToNoSelectionState();
        }
        else{
            System.out.println("Not enough money, please insert " + (-diff) + " more.");
        }
    }

    @Override
    public int cancelTransaction() {
        // TODO Auto-generated method stub
        int insertedMoney = vendingMachine.getInsertedMoney();
        vendingMachine.setSelectedItem(null);
        vendingMachine.emptyInsertedMoney();
        vendingMachine.changeToNoSelectionState();
        return insertedMoney;
    }

    @Override
    public String toString(){
        return "InsertedMoney";
    }
}
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://aaronice.gitbook.io/object-oriented-design/ood-case-studies/vending-machine.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.