1 package com.example.jdk8.lambda;
2
3 import org.springframework.core.convert.converter.Converter;
4
5 import java.awt.*;
6 import java.nio.file.DirectoryStream;
7 import java.time.*;
8 import java.time.format.DateTimeFormatter;
9 import java.time.format.FormatStyle;
10 import java.time.temporal.ChronoUnit;
11 import java.util.*;
12 import java.util.List;
13 import java.util.concurrent.TimeUnit;
14 import java.util.function.Function;
15 import java.util.function.Predicate;
16 import java.util.stream.Collectors;
17 import java.util.stream.Stream;
18
19 /**
20 * @program: jdk8
21 * @description: 接口的默认方法
22 * @author: hh.g
23 * @create: 2019-03-24 10:51:54
24 */
25 @FunctionalInterface
26 interface Formula {
27 double calculate(int a);
28
29 default double sqrt(int a) {
30 return Math.sqrt(a);
31 }
32 }
33
34 class Something {
35 String startsWith(String s) {
36 return String.valueOf(s.charAt(0));
37 }
38 }
39
40 class Person {
41 String firstName;
42 String lastName;
43
44 public Person() {
45 }
46
47 public Person(String firstName, String lastName) {
48 this.firstName = firstName;
49 this.lastName = lastName;
50 }
51 }
52
53 interface PersonFactory<P extends Person> {
54 P crete(String firstName, String lastName);
55 }
56
57
58 public class Demo04 {
59
60 //Lambda表达式
61 public static void lambdaSort() {
62 List<String> names = Arrays.asList("peter", "anna", "mike", "xenia");
63 Collections.sort(names, Comparator.naturalOrder());
64 names.forEach(i -> System.out.println("i = " + i));
65 }
66
67 //函数式接口
68 public static void interfaceMethod() {
69 Converter<String, Integer> converter1 = Integer::valueOf;
70 Converter<String, Integer> converter = (from) -> Integer.valueOf(from);
71 Integer convert = converter.convert("123");
72 System.out.println(convert);
73 }
74
75 //引用对象方法
76 public static void quoteMethod() {
77 Something something = new Something();
78 Converter<String, String> startsWith = something::startsWith;
79 String java = startsWith.convert("Java");
80 System.out.println("java = " + java);
81 }
82
83 //调用多个构造参数的函数
84 public static void test() {
85 PersonFactory<Person> personPersonFactory = Person::new;
86 Person crete = personPersonFactory.crete("Java", "Web");
87
88 }
89
90 public static void test02() {
91 Person person = new Person();
92 Predicate<String> keyEventDispatcher = (s) -> s.length() > 0;
93 System.out.println(keyEventDispatcher.test("foo"));
94 System.out.println(keyEventDispatcher.negate().test("foo"));
95 Predicate<String> isEmpty = String::isEmpty;
96 Predicate<Boolean> nonNull = Objects::nonNull;
97 System.out.println(nonNull.negate());
98 System.out.println(isEmpty.test(""));
99
100
101 }
102
103
104 public static void test03() {
105 Function<String, Integer> formula = Integer::valueOf;
106 Function<String, String> stringStringFunction = formula.andThen(String::valueOf);
107 String apply = stringStringFunction.apply("123");
108 System.out.println(apply);
109 }
110
111 public static void test04() {
112 List<String> list = new ArrayList<>();
113 list.add("aaaa");
114 list.add("bbbb");
115 list.add("a1a11a");
116 //输出
117 list.stream().filter(s -> s.startsWith("a")).forEach(System.out::println);
118 //排序输出
119 list.stream().sorted().filter(s -> s.startsWith("a")).forEach(System.out::println);
120 //降序
121 list.stream().sorted(Comparator.reverseOrder()).forEach(System.out::println);
122 //Map映射
123 list.stream().map(String::toUpperCase).sorted(Comparator.naturalOrder()).forEach(System.out::println);
124 Stream<String> sorted = list.stream().map(String::toUpperCase).sorted(Comparator.naturalOrder());
125 Set<String> collect = sorted.collect(Collectors.toSet());
126 //Match匹配
127 boolean a = list.stream().anyMatch(s -> s.startsWith("a"));
128 System.out.println("a = " + a);
129 //判断是否全为a开头的
130 System.out.println(list.stream().allMatch(s -> s.startsWith("a")));
131 //判断一个字符在该集合中是否存在
132 System.out.println(list.stream().noneMatch(s -> s.startsWith("z")));
133 System.out.println("==================Count计数=======================");
134 System.out.println("存在的数据有" + list.stream().filter(s -> s.startsWith("a")).count());
135 Optional<String> reduce = list.stream().sorted().reduce((s1, s2) -> s1 + "#" + s2);
136 reduce.ifPresent(System.out::println);
137 //reduce规约
138 String reduce1 = Stream.of("A", "B", "C", "D").reduce("*", String::concat);
139 System.out.println(reduce1);
140
141 }
142
143 /**
144 * Parallel Stream 并行流
145 */
146 public static void demo05() {
147 int max = 1000000;
148 List<String> list = new ArrayList<>(max);
149 for (int i = 0; i < max; i++) {
150 UUID uuid = UUID.randomUUID();
151 list.add(uuid.toString());
152 }
153
154 //串行排序（Sequential）
155 long t0 = System.nanoTime();
156 long count = list.stream().sorted().count();
157 System.out.println("count = " + count);
158 long t1 = System.nanoTime();
159 long millis = TimeUnit.NANOSECONDS.toMillis(t1 - t0);
160 System.out.println(String.format("sequential sort took %d ms", millis));
161
162 //并行排序(paralel)
163 long fisttime = System.nanoTime();
164 System.out.println(list.parallelStream().sorted().count());
165 long endTime = System.nanoTime();
166 long total = TimeUnit.NANOSECONDS.toMillis(endTime - fisttime);
167 System.out.println(String.format("parallel sort took: %d ms", total));
168
169 }
170
171 /**
172 * Maps
173 */
174 public static void demo06() {
175 Map<Integer, String> map = new HashMap<>();
176 for (int i = 0; i < 10; i++) {
177 //如果存在则不往里面存储，不存在则进行存储
178 map.putIfAbsent(i, "val" + i);
179 }
180 //putIfAbsent 阻止我们在null检查时写入额外的代码; forEach接受一个 consumer 来对 map 中的每个元素操作。
181 map.forEach((id, val) -> System.out.println(val));
182 System.out.println("================对map的操作===============");
183 //只对已存在的数据进行操作
184 map.computeIfPresent(3, (num, val) -> val + num);
185 System.out.println(map.get(3));
186
187 map.computeIfPresent(9, (num, value) -> null);
188 System.out.println(map.containsKey(9));
189 //当该key不存在时才会起作用
190 map.computeIfAbsent(23, num -> "val" + num);
191 System.out.println(map.get(23));
192
193 map.putIfAbsent(3, "bam");
194 System.out.println(map.get(3));
195 // 此方法不论存不存在都在执行完成后添加
196 map.compute(3,(key,value)->"测试数据");
197 System.out.println(map.get(3));
198
199 // 接下来展示如何在Map里删除一个键值全部匹配的项
200 //此方法表示，必须键和值都匹配才进行删除
201 map.remove(2,"val2");
202 map.forEach((key,value)-> System.out.println(key+"==="+value));
203 //该方法存在一个默认值，当集合中不存在该键时则返回后面的默认值
204 String not_found = map.getOrDefault(42, "not found");
205 System.out.println("not_found = " + not_found);
206 System.out.println("===========merge方法的使用（合并）");
207 // 对map元素进行合并也变得很容易
208 //merge做的事是如果键名不存在再插入，否则则对原键对应的值做合并操作，重新插入到map中
209 map.merge(9,"val9",(value,newValue)->value.concat(newValue));
210 map.forEach((key,value)-> System.out.println(key+"==="+value));
211 map.merge(9,"concat",(value,newValue)->value.concat(newValue));
212 System.out.println(map.get(9));
213 }
214
215 /**
216 * Date API 的使用
217 */
218 public static void demo07(){
219 System.out.println("=================Date API================");
220 Clock clock = Clock.systemDefaultZone();
221 long millis = clock.millis();
222 System.out.println("millis = " + millis);
223 Instant instant = clock.instant();
224 System.out.println("instant = " + instant);
225 Date legacyDate = Date.from(instant);
226 System.out.println("legacyDate = " + legacyDate);
227
228 // Timezones(时区)
229 System.out.println(ZoneId.getAvailableZoneIds());
230 ZoneId zone1 = ZoneId.of("Europe/Berlin");
231 ZoneId zone2 = ZoneId.of("Brazil/East");
232 System.out.println("zone1.getRules() = " + zone1.getRules());
233 System.out.println("zone2.getRules() = " + zone2.getRules());
234 // LocalTime(本地时间)
235 LocalTime now1 = LocalTime.now(zone1);
236 LocalTime now2 = LocalTime.now(zone2);
237 System.out.println(now1.isBefore(now2));
238
239 LocalTime late = LocalTime.of(15, 10, 20);
240 System.out.println("late = " + late);
241 DateTimeFormatter formatter = DateTimeFormatter.ofLocalizedTime(FormatStyle.SHORT).withLocale(Locale.GERMAN);
242 LocalTime parse = LocalTime.parse("13:37", formatter);
243 System.out.println("parse = " + parse);
244 // LocalDate 本地日期
245 LocalTime now = LocalTime.now();
246 System.out.println("now = " + now);
247 System.out.println("================LocalDate=================");
248 LocalDate today = LocalDate.now();
249 System.out.println("今天的日期 = " + today);
250 LocalDate tomorrow = today.plus(1, ChronoUnit.DAYS);
251 System.out.println("明天的日期 = " + tomorrow);
252 LocalDate yesterday = today.minusDays(1);
253 System.out.println("昨天的日期 = " + yesterday);
254 LocalDate of = LocalDate.of(2019, Month.MARCH, 24);
255 DayOfWeek dayOfMonth = of.getDayOfWeek();
256 int dayOfMonth1 = of.getDayOfMonth();
257 System.out.println("今天是周几："+dayOfMonth);
258 System.out.println("今天是"+dayOfMonth1);
259 System.out.println(of.getMonthValue());
260 // 格式化日期
261 String str = "2019-03-24 15时34分40秒";
262 DateTimeFormatter formatter1 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH时mm分ss秒");
263 LocalDate parse1 = LocalDate.parse(str, formatter1);
264 System.out.println("parse1 = " + parse1);
265
266 LocalDateTime now3 = LocalDateTime.now();
267 String format = DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(now3);
268 System.out.println("format = " + format);
269 DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("YYYY-MM-dd HH:mm:ss");
270 System.out.println(dateTimeFormatter.format(now3));
271 }
272
273
274
275 public static void main(String[] args) {
276 //TODO 通过匿名内部类的方式访问接口
277 Formula formula = new Formula() {
278 @Override
279 public double calculate(int a) {
280 return sqrt(a * 100);
281 }
282 };
283 System.out.println(formula.calculate(100));
284 System.out.println(formula.sqrt(16));
285 lambdaSort();
286 interfaceMethod();
287 quoteMethod();
288 test02();
289 test03();
290 test04();
291 //demo05();
292 demo06();
293 demo07();
294 }
295 }
