Java9を迎えた今こそ！Java本格(再)入門

Acroquest Technology Co., Ltd.

Copyright © Acroquest Technology Co., Ltd. All rights reserved.
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Java  
Chapter 7  
Chapter 8  
Chapter 9  
Chapter 12  
Acroquest Technology  
- 2017 3  
2Twitter: @omochiya
-

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1.Introduction
2.Java 1.4 -> 5.0
3.Java 5.0 -> 7
4.Java 7 -> 8
5.Java 8 -> 9
6.Java 9 -> Future
5

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CSV File
2017-09-25,100,123456,Acroquest,
2017-10-02,100,-28980, ,
2017-10-03,100,-17712, ,
2017-10-20,100,3000000,gihyo,
2017-10-25,100,200000,Acroquest,
 
, , , ,
etc

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List read(String fileName) {
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
List list = new ArrayList();
BufferedReader reader = null;
try {
reader = new BufferedReader(new InputStreamReader(new FileInputStream(fileName), "UTF-8"));
String line;
while ((line = reader.readLine()) != null) {
String[] s = line.split(",");
Transaction tx = new Transaction();
tx.date = df.parse(s[0]);
tx.accountId = s[1];
tx.amount = Integer.valueOf(s[2]);
tx.name = s[3];
tx.note = s[4];
list.add(tx);
}
} catch (ParseException e) {
throw new RuntimeException("failed to parse date", e);
} catch (IOException e) {
throw new RuntimeException("failed to read file: " + fileName, e);
} finally {
try {
if (reader != null) {
reader.close();
}
// ignore
}
}
return list;
}
CSV

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try {
reader = new BufferedReader(new InputStreamReader( 
new FileInputStream(fileName), "UTF-8"));
CSV

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String line;
tx.name = s[3];
tx.note = s[4];
list.add(tx); 
}
CSV

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} finally {
try {
reader.close();
}
// ignore
}
}
return list;
}
finally close
CSV

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Transaction
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class Transaction {
Date date;
String accountId;
Integer amount;
String name;
String note;
public Transaction() {
}
public Transaction(Date date, String accountId, Integer amount, String name, String note) {
this.date = date;
this.accountId = accountId;
this.amount = amount;
this.name = name;
this.note = note;
}
public String toString() {
return date + " " + accountId + " " + amount + " " + name + " " + note;
}
}
CSV

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Transaction 1/2
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class Transaction {
Date date;
String accountId;
Integer amount;
String name;
String note;
}
CSV

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Transaction 2/2
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public Transaction(Date date, String accountId, Integer amount,  
String name, String note) {
this.date = date;
this.name = name;
this.note = note;
}
}
}
CSV

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List list = read(fileName);
int sum = 0;
for (int i = 0; i < list.size(); i++) {
Transaction tx = (Transaction) list.get(i);
sum += tx.amount;
}
System.out.println(sum);
CSV

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Calendar cal = Calendar.getInstance();
cal.setTime(tx.date);
if (cal.get(Calendar.MONTH) == 5) {
System.out.println(tx);
}
}
0
CSV

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try {
CSV

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List<Transaction> read(String fileName) {
List<Transaction> list = new ArrayList<Transaction>();
try {
CSV

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try {
Generics  
→  
→
CSV

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int sum = 0;
sum += tx.amount;
}
CSV

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List<Transaction> list = read(fileName);
int sum = 0;
for (Transaction tx : list) {
sum += tx.amount;
}
CSV

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int sum = 0;
sum += tx.amount;
}
CSV
for  
→

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Transaction 2/2
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this.date = date;
this.name = name;
this.note = note;
}
}
}
CSV

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Transaction 2/2
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this.date = date;
this.name = name;
this.note = note;
}
@Override
}
}
CSV

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Transaction 2/2
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this.date = date;
this.name = name;
this.note = note;
}
@Override
}
}
 
→ Override
CSV

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try {
CSV

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List<Transaction> list = new ArrayList<>();
try (BufferedReader reader =
Files.newBufferedReader(Paths.get(fileName),
StandardCharsets.UTF_8)) {
CSV

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CSV

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try-with-resoureces  
try ( ) close  
→  
→  
CSV

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Files nio2
CSV

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String Charset  
StandardCharsets  
→
CSV

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} finally {
try {
reader.close();
}
// ignore
}
}
return list;
}
CSV

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} catch (ParseException | IOException e) {
throw new RuntimeException("failed to parse date or read file”, e);
}
return list;
}
catch  
CSV

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Transaction toString
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class Transaction {
Date date;
String accountId;
Integer amount;
String name;
String note;
}
public Transaction(Date date, String accountId, Integer amount, String name, String note)
{
this.date = date;
this.name = name;
this.note = note;
}
CSV

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class Transaction {
LocalDate date;
String accountId;
Integer amount;
String name;
String note;
}
public Transaction(LocalDate date, String accountId, Integer amount, String name, String
note) {
this.date = date;
this.name = name;
this.note = note;
}
CSV

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class Transaction {
LocalDate date;
String accountId;
Integer amount;
String name;
String note;
}
public Transaction(LocalDate date, String accountId, Integer amount, String name, String
note) {
this.date = date;
this.name = name;
this.note = note;
}
Date and Time API 
→LocalDate  
LocalDateTime LocalTime  
OffsetDateTime ZonedDateTime  
CSV

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try (BufferedReader reader = Files.newBufferedReader(Paths.get(fileName),
String line;
tx.name = s[3];
tx.note = s[4];
list.add(tx); 
}
CSV

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// SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
try (BufferedReader reader = Files.newBufferedReader(Paths.get(fileName))) {
String line;
tx.date = LocalDate.parse(s[0]);
tx.name = s[3];
tx.note = s[4];
list.add(tx); 
}
CSV

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// SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
String line;
tx.name = s[3];
tx.note = s[4];
list.add(tx); 
}
UTF-8 Charset
 
ISO 8601  
CSV

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Calendar cal = Calendar.getInstance();
cal.setTime(tx.date);
if (cal.get(Calendar.MONTH) == 5) {
}
}
CSV

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if (tx.date.getMonth() == Month.JUNE) {
}
}
CSV

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}
}
enum  
enum  
→ 0  
CSV

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String line;
tx.name = s[3];
tx.note = s[4];
list.add(tx); 
}
throw new RuntimeException("failed to parse date or read file”, e);
}
return list;
CSV

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try (Stream<String> stream = Files.lines(Paths.get(fileName))) {
return stream
.map(line -> {
tx.name = s[3];
tx.note = s[4];
return tx;
})
.collect(Collectors.toList());
throw new UncheckedIOException("failed to read file", e);
}
CSV

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return stream
.map(line -> {
tx.name = s[3];
tx.note = s[4];
return tx;
})
}
 
Stream  
List
CSV
 
String Transaction

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return stream
.map(line -> {
tx.name = s[3];
tx.note = s[4];
return tx;
})
}
Lambda
CSV

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//
//
}
//
int sum = 0;
sum += tx.amount;
}
CSV

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//
read(fileName).stream()
.forEach(System.out::println);
//
int sum = read(fileName).stream()
.mapToInt(tx -> tx.amount)
.sum();
CSV

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//
//
.sum();
int
CSV

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//
//
.sum();
Lambda
CSV

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// 6  
}
}
CSV

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// 6
.filter(tx -> tx.date.getMonth() == Month.JUNE)
CSV

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// 6
6
filter
CSV

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// 6
Lambda

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return stream
.map(line -> {
tx.name = s[3];
tx.note = s[4];
return tx;
})
}
 
String Transaction
List

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//
//
.sum();
 
int

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// 6
6
filter

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JShell
102
//
jshell> List<Integer> intList = List.of(1, 2, 3);
intList ==> [1, 2, 3]
jshell> List<String> strList = List.of("aaa,", "bbb", “ccc");
strList ==> [aaa,, bbb, ccc]
jshell> intList.add(4);
| java.lang.UnsupportedOperationException thrown:
| at ImmutableCollections.uoe (ImmutableCollections.java:71)
( )

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JShell
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//
jshell> Map<Integer, String> map =  
Map.of(1, "aaa", 2, "bbb", 3, “ccc");
map ==> {1=aaa, 2=bbb, 3=ccc}
jshell> map.put(4, "ddd");
| java.lang.UnsupportedOperationException thrown:
| at ImmutableCollections.uoe (ImmutableCollections.java:71)
( )

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//
var str = “Hello”;
final var MAXIMUM = 100L;
// NG
var array = {1, 2, 3};
var list = new ArrayList<>();

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Java9を迎えた今こそ！Java本格(再)入門

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