1 /* 2 * Copyright (C) 2019 The Dagger Authors. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package dagger.example.atm; 18 19 import java.math.BigDecimal; 20 import java.util.HashMap; 21 import java.util.Map; 22 import javax.inject.Inject; 23 import javax.inject.Singleton; 24 25 /** A database that stores all of its data in memory. */ 26 @Singleton 27 final class InMemoryDatabase implements Database { 28 private final Map<String, Account> accounts = new HashMap<>(); 29 30 @Inject InMemoryDatabase()31 InMemoryDatabase() {} 32 33 @Override getAccount(String username)34 public Account getAccount(String username) { 35 return accounts.computeIfAbsent(username, InMemoryAccount::new); 36 } 37 38 private static final class InMemoryAccount implements Account { 39 private final String username; 40 private BigDecimal balance = BigDecimal.ZERO; 41 InMemoryAccount(String username)42 InMemoryAccount(String username) { 43 this.username = username; 44 } 45 46 @Override username()47 public String username() { 48 return username; 49 } 50 51 @Override deposit(BigDecimal amount)52 public void deposit(BigDecimal amount) { 53 checkNonNegative(amount, "deposit"); 54 balance = balance.add(amount); 55 } 56 57 @Override withdraw(BigDecimal amount)58 public void withdraw(BigDecimal amount) { 59 checkNonNegative(amount, "withdraw"); 60 balance = balance.subtract(amount); 61 } 62 checkNonNegative(BigDecimal amount, String action)63 private void checkNonNegative(BigDecimal amount, String action) { 64 if (amount.signum() == -1) { 65 throw new IllegalArgumentException( 66 String.format("Cannot %s negative amounts: %s", action, amount)); 67 } 68 } 69 70 @Override balance()71 public BigDecimal balance() { 72 return balance; 73 } 74 } 75 } 76