Java: The Past and Present

Transcript

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24. final Class a = List.class; final Class b = String.class;

    final Class c = double.class; final Class d = int[][].class; • •

25. import java.awt.Event; public class MyApp extends java.applet.Applet { public boolean

    action(Event evt, Object arg) { if (evt.target == APPROVE_BUTTON) { return doSomething1(evt, arg); } else if (evt.target == REJECT_BUTTON) { return doSomething2(evt, arg); } else if (evt.target == DATE_CHOICE) { return doSomething3(evt, arg); } … return super.action(evt, arg); } import java.awt.event.*; public class MyApp2 extends java.applet.Applet { public void init() { this.addMouseListener(new MyMouseAdapter()); Button approveButton = new Button("承認"); approveButton.addActionListener(new ApproveListner()); this.add(approveButton); } }

26. import java.awt.event.*; public class MyApp2 extends java.applet.Applet { public void

    init() { this.addMouseListener(new MyMouseAdapter()); Button approveButton = new Button("承認"); approveButton.addActionListener(new ApproveListner()); this.add(approveButton); } } import java.awt.event.*; public class ApproceListner implements ActionListener { public void actionPerformed(final ActionEvent e) { // 承認 // 承認 // 承認 } }

27. import java.awt.event.*; public class MyApp3 extends java.applet.Applet { public class

    ApproceListner implements ActionListener { public void actionPerformed(final ActionEvent e) { // 承認 // 承認 // 承認 } } public void init() { this.addMouseListener(new MyMouseAdapter()); Button approveButton = new Button("承認"); approveButton.addActionListener(new ApproveListner()); this.add(approveButton); } } • • •

28. import java.awt.event.*; public class MyApp3 extends java.applet.Applet { public class

    ApproceListner implements ActionListener { public void actionPerformed(final ActionEvent e) { // 承認 // 承認 // 承認 } } public void init() { this.addMouseListener(new MyMouseAdapter()); Button approveButton = new Button("承認"); approveButton.addActionListener(new ApproveListner()); this.add(approveButton); } }

29. import java.awt.event.*; public class MyApp4 extends java.applet.Applet { public void

    init() { this.addMouseListener(new MyMouseAdapter()); Button approveButton = new Button("承認"); approveButton.addActionListener(new ActionListener() { public void actionPerformed(final ActionEvent e) { // 承認 // 承認 // 承認 } }); this.add(approveButton); } } • • •

30. import java.awt.event.*; public class MyApp4 extends java.applet.Applet { public void

    init() { this.addMouseListener(new MyMouseAdapter()); Button approveButton = new Button("承認"); approveButton.addActionListener(new ActionListener() { public void actionPerformed(final ActionEvent e) { // 承認 // 承認 // 承認 } }); this.add(approveButton); } }

31. import java.awt.event.*; public class MyApp4 extends java.applet.Applet { public void

    init() { this.addMouseListener(new MyMouseAdapter()); Button approveButton = new Button("承認"); approveButton.addActionListener({ // 承認 // 承認 // 承認 }); this.add(approveButton); } } 結果 = sort(users, 名前でソート); 結果 = sort(users, 年齢でソート); 結果 = sort(users, 所属部署でソート); 結果 = filter(users, 名古屋に住んでいる); 結果 = filter(users, 関数型言語が好きである); 結果 = filter(users, リア充である); 結果 = transform(users, 名前を大文字に); 結果 = transform(users, 給与を半分に);

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49. List list = (List) Proxy.newProxyInstance(List.class.getClassLoader(), new Class[]{ List.class }, new

    MyInvocationHandler());
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55. • • try { doSomething(); } catch (LowLevelException cause) {

    throw new HighLevelException( "••が▲▲です", cause); }

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61. • • • • Charset sjis = Charset.forName("Shift-JIS"); InputStream is

    = new FileInputStream(new File("hoge.txt")); Reader reader = new BufferedReader(new InputStreamReader(is, sjis));

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66. List names = ……; names.add(9999); for (int i = 0;

    i < names.size(); i++) { String name = (String) names.get(i); System.out.println(name); }
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68. • • List names = ……; for (int i =

    0; i < names.size(); i++) { // まじこわいキャスト String name = (String) names.get(i); System.out.println(name); } // 中身なんて知ったことか！！ names.add(9999); List<String> names = ……; for (int i = 0; i < names.size(); i++) { String name = names.get(i); System.out.println(name); } names.add(9999);
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72. int pri = 1; Integer b = Integer.valueOf(pri); int pri

    = 1; Integer b = pri;

73. @Test(expected = NoSuchElementException.class) @Ignore public void getShouldFailIfEmtpy() { Optional.empty().get(); }

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75. public enum Imoni { YAMAGATA, FUKUSHIMA, MIYAGI, MIX; } public

    enum Suite { SPADE, HEART, CLUB, DIAMOND; } public enum Janken { ROCK, PAPER, SCISSOR; } public enum JapaneseProvince { TOKYO, HOKKAIDO, … AICHI, … OKINAWA } assert Suite.SPADE != Suite.HEART; assert Suite.SPADE != Janken.ROCK;

76. • • • public enum Planet { MERCURY(3.303e+23, 2.4397e6), VENUS(4.869e+24,

    6.0518e6), EARTH(5.976e+24, 6.37814e6), MARS(6.421e+23, 3.3972e6), JUPITER(1.9e+27, 7.1492e7), SATURN(5.688e+26, 6.0268e7), URANUS(8.686e+25, 2.5559e7), NEPTUNE(1.024e+26, 2.4746e7); private final double mass; private final double radius; Planet(double mass, double radius) { this.mass = massKillogram; this.radius = radiusMeter; } public static final double G = 6.67300E-11; public double surfaceGravity() { return G * mass / (radius * radius); }

77. Set<Planet> 全部 = EnumSet.allOf(Planet.class); Set<Planet> 地球以外 = EnumSet.complementOf(EnumSet.of(EARTH)); Map<Imoni, Integer>

    芋煮種人気 = new EnumMap<Imoni, Integer>(Imoni.class); 芋煮種人気.put(Imoni.FUKUSHIMA, 1024); 芋煮種人気.put(Imoni.YAMAGATA, 256); 芋煮種人気.put(Imoni.MIX, -9999);

78. List<String> src = Arrays.asList("Java", "Scala", "Clojure"); Set<String> langs = new

    HashSet<>(src); Iterator<String> iterator = langs.iterator(); while (iterator.hasNext()) { String e = iterator.next(); System.out.println(e); } Iterator<String> iterator2 = langs.iterator(); for (String e; iterator2.hasNext(); ) { e = iterator2.next(); System.out.println(e); } String[] array = {"Ruby", "Python", "JavaScript"}; for (int i = 0; i < array.length; i++) { String e = array[i]; System.out.println(e); } for (final String e : langs) { System.out.println(e); } for (final String e : array) { System.out.println(e); }
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80. Maybe<String> maybeName = …; Maybe<Integer> maybeAge = …; for (String

    name : maybeName) { for (int age : maybeAge) { return String.format("%sさんは%s歳です", name, age); } } return "そんな人はいないか、年齢が分かりません!!";

81. public static int sum(int... ints) { int sum = 0;

    for (int i : ints) { sum += i; } return sum; } public static void main(String... args) { System.out.println(sum(1)); System.out.println(sum(2, 3, 4)); System.out.println(sum(new int[]{5, 6})); }

82. import static java.lang.Math.random; import static java.lang.Math.floor; public class NewStyle {

    public static void main(String[] args) { double x = floor(random() * 100); System.out.println(x); } } public class FormerStyle { public static void main(String[] args) { double d = Math.floor(Math.random() * 100); System.out.println(d); } }

83. List<String> mutableList = newArrayList("Java", "Scala", "Clojure"); Set<String> mutableSet = newHashSet("Java",

    "Scala", "Clojure");
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90. // 先頭からn件 final String[] original = {"Java", "Scala", "F#", "C#",

    "Haskell", "Python"}; final String[] first3 = Arrays.copyOf(original, 3); assertThat(first3, is(new String[]{"Java", "Scala", "F#"})); // i番目～j-1番目まで final int[] original2 = {0, 10, 20, 30, 40, 50}; final int[] range = Arrays.copyOfRange(original2, 3, 5); assertThat(range, is(new int[]{30, 40}));
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93. @Override @SuppressWarnings("unchecked") public void actionPerformed(final ActionEvent e) { return (Class<T>)

    foo.getClass(); }

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105. ZipFile zf = new ZipFile(zipFileName); try { BufferedWriter writer =

     Files.newBufferedWriter(outputPath, charset); try { for (ZipEntry entry : Collections.list(zf.entries())) { String entryName = entry.getName() + newLine; writer.write(entryName, 0, entryName.length()); } } finally { writer.close(); } } finally { zf.close(); } try (ZipFile zf = new ZipFile(zipFileName); BufferedWriter writer = Files.newBufferedWriter(outputPath, charset)) { for (ZipEntry entry : Collections.list(zf.entries())) { String entryName = entry.getName() + newLine; writer.write(entryName, 0, entryName.length()); } }

106. List<Integer> list = new ArrayList<Integer>(); Map<String, List<String>> bag; bag =

     new HashMap<String, List<String>>(); List<Integer> list = new ArrayList<>(); Map<String, List<String>> bag; bag = new HashMap<>();

107. String[] array = {"おおさか", "なごや", "ふくおか"}; for (String name :

     array) { switch (name) { case "なごや": System.out.println("こわい"); break; default: System.out.println("こわくない"); } } • • •

108. try { FileInputStream is = new FileInputStream(new File("")); Document doc

     = DocumentBuilderFactory.newInstance() .newDocumentBuilder() .parse(is); } catch (IOException e) { // 例外処理 } catch (ParserConfigurationException e) { // 例外処理 } catch (SAXException e) { // 例外処理 } try { FileInputStream is = new FileInputStream(new File("")); Document doc = DocumentBuilderFactory.newInstance() .newDocumentBuilder() .parse(is); } catch (IOException ex) { // IO系例外処理 } catch (ParserConfigurationException | SAXException ex) { // XML系例外処理 } • •

109. final int[] phases = { 0b00110001, 0b01100010, 0b11000100, 0b10001001, 0b00010011,

     0b00100110, 0b01001100, 0b10011000 }; final int[] phases = { Integer.parseInt("00110001", 2), Integer.parseInt("01100010", 2), Integer.parseInt("11000100", 2), Integer.parseInt("10001001", 2), Integer.parseInt("00010011", 2), Integer.parseInt("00100110", 2), Integer.parseInt("01001100", 2), Integer.parseInt("10011000", 2) }; int bin = 0b00_11_01_01_01_01; int oct = 0123_4567; int hex = 0xCAFE_BABE;

110. • • • • • List<Integer> list = #[1, 2,

     3]; Set<Integer> set = #[1, 2, 3]; Map<String, Integer> map = #{ "foo": 1, "bar": 2 }; int[] array = {1, 2, 3};

111. public Foo(Object bar, Object[] buz) { this.bar = Objects.requireNonNull(bar); this.buz

     = Objects.requireNonNull(buz, "buzはnullダメ"); } @Override public boolean equals(Object o) { if (o == null || o instanceof Foo) return false; Foo that = (Foo) o; return Objects.equals(this.bar, that.bar) && Objects.deepEquals(this.buz, that.buz); } @Override public int hashCode() { return Objects.hash(this.bar, this.buz); } • •

112. // Windows ¥r¥n, Linux ¥n, 昔のMac ¥r String nicerNewLine =

     System.lineSeparator(); // Windows ¥r¥n, Linux ¥n, 昔のMac ¥r String newLine = System.getProperty("line.separator");
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115. Path p1 = Paths.get("path/to/file"); assert !p1.isAbsolute(); Path p2 = Paths.get("/usr/bin/curl");

     assert p2.isAbsolute(); Path p3 = Paths.get("path/foo"); Path 相対パス = p1.relativize(p3); /* ../../foo */ assert p1.getParent().endsWith("to"); assert p2.getRoot() != null; assert p1.getNameCount() == 3; assert p1.compareTo(p3) > 0;

116. Path link = Files.createLink(Paths.get("newFile"), Paths.get("existingFile")); List<String> eager = Files.readAllLines(Paths.get("hoge.txt"), Charset.forName("Shift_JIS"));

     Reader reader = Files.newBufferedReader(Paths.get("hoge.txt"), Charset.forName("EUC-JP"));

117. DirectoryStream<Path> stream = Files.newDirectoryStream(Paths.get("画像フォルダ"), new DirectoryStream.Filter<Path>() { @Override public boolean

     accept(final Path entry) throws IOException { return !Files.isDirectory(entry); } }); for (Path 画像 : stream){ // 何か }

118. Path bar = FileSystems.getDefault().getPath("foo/bar"); WatchService watchService = FileSystems.getDefault().newWatchService(); bar.register(watchService, StandardWatchEventKinds.ENTRY_CREATE,

     StandardWatchEventKinds.ENTRY_MODIFY, StandardWatchEventKinds.ENTRY_DELETE); while (!Thread.currentThread().isInterrupted()) { System.out.println("監視中..."); WatchKey watchKey = watchService.take(); if (watchKey.isValid()) { for (WatchEvent<?> event : watchKey.pollEvents()) { System.out.printf("イベント発生: %s", event.kind()); Path context = FileSystems.getDefault().getPath("¥¥" + event.context()); process(context, event); } } }

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125. import java.awt.event.*; public class MyApp4 extends java.applet.Applet { public void

     init() { this.addMouseListener(new MyMouseAdapter()); Button approveButton = new Button("承認"); approveButton.addActionListener(new ActionListener() { @Override public void actionPerformed(final ActionEvent evt) { // 承認 // 承認 // 承認 } }); this.add(approveButton); } }

126. Button approveButton = new Button("承認"); approveButton.addActionListener(evt -> { // do

     something !! });

127. Collections.sort(names, new Comparator<String>() { @Override public int compare(final String a,

     final String b) { return 0/*ここに比較ロジックが入ります*/; } }); 引数 -> 処理

128. BinaryOperator<String> longer = (String a, String b) -> { return

     a.length() >= b.length() ? a : b; }; longer = (a, b) -> { return a.length() >= b.length() ? a : b; }; longer = (a, b) -> a.length() >= b.length() ? a : b; supplier = () -> Math.random(); toSet = arg -> Collections.singleton(arg);

129. Set<Lang> langs = EnumSet.of(JAVA, SCALA, CLOJURE, C_SHARP, F_SHARP, OCAML, RUBY,

     PYTHON, HASKELL, JAVASCRIPT); List<String> collect = langs.stream() .filter(lang -> lang.isStaticallyTyped()) .map(lang -> lang.displayName()) .sorted() .collect(toList());

130. Set<Lang> langs = … List<String> collect = langs.stream() .filter(lang ->

     lang.isStaticallyTyped()) • • interface Collection<E> { default Stream<E> stream() { return …; } }

131. interface Worker { default void work() {…} } interface Person

     { default void eat() {…} default void play() {…} default void sleep() {…} } class Programmer implements Worker, Person { public void aDayInTheLife() { this.eat(); if (Today.isWeekday()) { this.work(); } else { this.play(); } this.sleep(); } }

132. public String foo(User user) { if (user == null) {

     return "不明なユーザ"; } else { return user.name(); } } public String bar(Optional<User> user) { return user.map(user_ -> user_.name()) .orElse("不明なユーザ"); } public Optional<User> find(long id) { User user = hoge(id); return Optional.ofNullable(user); }
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