[新]Java8的新特性 - IT评测·应用市场-qidao123.com

@Test
public void test() {
TreeSet<Integer> treeSet = new TreeSet<>(new Comparator<Integer>() {
@Override
public int compare(Integer o1, Integer o2) {
return Integer.compare(o1, o2);
}
});
treeSet.add(20);
treeSet.add(78);
treeSet.add(-98);
System.out.println(treeSet);
}

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@Test
public void test() {
TreeSet<Integer> treeSet = new TreeSet<>((Integer x, Integer y) -> {
return x.compareTo(y);
});
treeSet.add(20);
treeSet.add(78);
treeSet.add(-98);
System.out.println(treeSet);
}

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@Test
public void test() {
TreeSet<Integer> treeSet = new TreeSet<>((x, y) -> x.compareTo(y));
treeSet.add(20);
treeSet.add(78);
treeSet.add(-98);
System.out.println(treeSet);
}

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@FunctionalInterface
interface Convert {
Integer fun(String s);
}
@Test
public void test8() {
Convert convert = from -> Integer.valueOf(from);
System.out.println(convert.fun("150") + 1);
}
@Test
public void test9() {
Convert convert = Integer::valueOf;
System.out.println(convert.fun("150") + 1);
}

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@FunctionalInterface
interface Convert {
Integer fun(String s);
}
@Test
public void test8() {
Convert convert = from -> "liuzijian.com".indexOf(from);
System.out.println(convert.fun("zi"));
}
@Test
public void test9() {
Convert convert = "liuzijian.com"::indexOf;
System.out.println(convert.fun("zi"));
}

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@FunctionalInterface
interface Fun {
String test(String a, int b, int c);
}
@Test
public void test8() {
Fun fun = (a, b, c) -> a.substring(b, c);
String s = fun.test("abcdefghi", 3, 5);
System.out.println(s);
}
@Test
public void test9() {
Fun fun = String::substring;
String s = fun.test("abcdefghi", 3, 5);
System.out.println(s);
}

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@FunctionalInterface
interface Fun {
BigDecimal test(String n);
}
@Test
public void test8() {
Fun fun = (n) -> new BigDecimal(n);
BigDecimal b = fun.test("45.64");
System.out.println(b);
}
@Test
public void test9() {
Fun fun = BigDecimal::new;
BigDecimal b = fun.test("45.64");
System.out.println(b);
}

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@FunctionalInterface
public interface MyPredicate<T> {
boolean fun(T obj);
default void other() {
System.out.println("hello world");
}
static void staticMethod() {
System.out.println("static method");
}
}

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@Data
@AllArgsConstructor
@NoArgsConstructor
@ToString
public class Employee {
private String name;
private Double salary;
private Integer age;
public Employee(Integer age) {
this.age = age;
}
public Employee(Integer age, String name) {
this.age = age;
this.name = name;
}
}

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private List<Employee> filter(List<Employee>employees, MyPredicate<Employee> predicate) {
List<Employee>list = new ArrayList<>();
for (Employee e : employees) {
if (predicate.fun(e)) {
list.add(e);
}
}
return list;
}

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private List<Employee> employees = Arrays.asList(
new Employee("soo", 8547.322, 17),
new Employee("lili", 1000D, 15),
new Employee("王萌", 2154D, 16),
new Employee("张帆", 8547.322, 22),
new Employee("goog", 353D, 12)
);
@Test
public void test3() {
List<Employee>list = filter(employees, new MyPredicate<Employee>() {
@Override
public boolean fun(Employee obj) {
return obj.getAge() > 16;
}
});
System.out.println(list);
}

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List<Employee>list2 = filter(employees, (e) -> e.getAge() < 16);

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private void testConsumer(String str, Consumer<String>consumer) {
consumer.accept(str);
}
private String testSupplier(Supplier<String>supplier) {
return supplier.get();
}
private Integer testFunction(String str, Function<String, Integer>function) {
return function.apply(str);
}
private boolean testPredicate(String str, Predicate<String>predicate) {
return predicate.test(str);
}

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@Test
public void test4() {
testConsumer("hello lambda", (x) -> System.out.println(x));
String str = testSupplier(() -> { return "hello world"; });
System.out.println(str);
Integer integer = testFunction("66", (x) -> Integer.valueOf(x));
System.out.println(integer);
boolean b = testPredicate("hello", (e) -> e.equals("hello"));
System.out.println(b);
}

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hello lambda
hello world
66
true

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@Test
public void test2() {
testConsumer("hello lambda", System.out::println);
Integer integer = testFunction("66", Integer::valueOf);
}

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List<String> list = new ArrayList<>();
Stream<String> stream = list.stream();

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Employee[] employees = new Employee[10];
Stream<Employee> employeeStream = Arrays.stream(employees);

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Employee[] employees = new Employee[10];
Stream<Employee> employeeStream1 = Stream.of(employees);

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Stream.iterate(10, (x) -> x + 2)
.limit(10)
.forEach(System.out::println);

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Stream.generate(Math::random)
.limit(20)
.forEach(System.out::println);

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@Test
public void test5() {
IntStream intStream = IntStream.builder()
.add(1)
.add(2)
.add(3)
.add(4).build();
// 下面的聚集方法每次只能执行一行
System.out.println(intStream.max().getAsInt());
//System.out.println(intStream.min().getAsInt());
//System.out.println(intStream.sum());
//System.out.println(intStream.count());
//System.out.println(intStream.average());
}

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private List<Employee> employees = Arrays.asList(
new Employee("soo", 8547.322, 17),
new Employee("lili", 1000D, 18),
new Employee("王萌", 2154D, 16),
new Employee("张帆", 8547.322, 22),
new Employee("张帆", 8547.322, 22),
new Employee("张帆", 8547.322, 22),
new Employee("goog", 353D, 12)
);
private List<String> list = Arrays.asList("aaa", "bbb", "ccc", "ddd", "eee");

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@Test
public void test() {
employees.stream()
.filter((e) -> {
// 中间操作
System.out.println("中间操作");
return e.getAge() > 16;
})
.limit(2) //中间操作
.forEach(System.out::println); //终止操作
}

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中间操作
Employee(name=soo, salary=8547.322, age=17)
中间操作
Employee(name=lili, salary=1000.0, age=18)

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@Test
public void test2() {
employees.stream().skip(2).forEach(System.out::println);
}

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Employee(name=王萌, salary=2154.0, age=16)
Employee(name=张帆, salary=8547.322, age=22)
Employee(name=张帆, salary=8547.322, age=22)
Employee(name=张帆, salary=8547.322, age=22)
Employee(name=goog, salary=353.0, age=12)

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//Employee类重写equals hashCode
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Employee employee = (Employee) o;
if (!Objects.equals(name, employee.name)) return false;
if (!Objects.equals(salary, employee.salary)) return false;
return Objects.equals(age, employee.age);
}
@Override
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + (salary != null ? salary.hashCode() : 0);
result = 31 * result + (age != null ? age.hashCode() : 0);
return result;
}

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@Test
public void test3() {
employees.stream().distinct().forEach(System.out::println);
}

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Employee(name=soo, salary=8547.322, age=17)
Employee(name=lili, salary=1000.0, age=18)
Employee(name=王萌, salary=2154.0, age=16)
Employee(name=张帆, salary=8547.322, age=22)
Employee(name=goog, salary=353.0, age=12)

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@Test
public void test5() {
List<String> list = Arrays.asList("aaa", "bbb", "ccc");
Function<String, Stream<Character>> function = (e) -> {
List<Character> characters = new ArrayList<>();
for (char c : e.toCharArray()) {
characters.add(c);
}
return characters.stream();
};
List<Character> collect = list.stream()
.flatMap(function)
.collect(Collectors.toList());
collect.forEach(System.out::println);
}

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a
a
a
b
b
b
c
c
c

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@Test
public void test4() {
employees.stream().map((e) -> e.getName()).forEach(System.out::println);
}

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soo
lili
王萌
张帆
张帆
张帆
goog

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@Test
public void test() {
list.stream().sorted().forEach(System.out::println);
}

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a
a
a
b
b
b
c
c
cdddeee

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@Test
public void test2() {
employees.stream()
.sorted((e1, e2) -> e1.getAge() - e2.getAge())
.forEach(System.out::println);
}

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Employee(name=goog, salary=353.0, age=12)
Employee(name=王萌, salary=2154.0, age=16)
Employee(name=soo, salary=8547.322, age=17)
Employee(name=lili, salary=1000.0, age=18)
Employee(name=张帆, salary=8547.322, age=22)
Employee(name=张帆, salary=8547.322, age=22)
Employee(name=张帆, salary=8547.322, age=22)

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@Test
public void test3() {
boolean b = employees.stream().allMatch((e) -> e.getAge() > 10);
System.out.println(b);
b = employees.stream().anyMatch((e) -> e.getAge() > 100);
System.out.println(b);
b = employees.stream().noneMatch((e) -> e.getAge() > 100);
System.out.println(b);
Optional<Employee> first = employees.stream().findFirst();
System.out.println(first.get());
Optional<Employee> any = employees.stream().findAny();
System.out.println(any.get());
long count = employees.stream().count();
System.out.println(count);
Optional<Employee> max = employees.stream()
.max(Comparator.comparingInt(Employee::getAge));
System.out.println(max.get());
Optional<Integer> maxAge = employees.stream()
.map(Employee::getAge)
.max(Integer::compare);
System.out.println(maxAge.get());
}

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true
false
true
Employee(name=soo, salary=8547.322, age=17)
Employee(name=soo, salary=8547.322, age=17)
7
Employee(name=张帆, salary=8547.322, age=22)
22

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@Test
public void test() {
List<Integer> list = Arrays.asList(1,2,3,4,5,6,7,8,9);
Integer sum = list.stream().reduce(0, Integer::sum);
System.out.println(sum);
Optional<Double> reduce = employees.stream().map(Employee::getSalary)
.reduce(Double::sum);
System.out.println(reduce.get());
}

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45
37696.288

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@Test
public void test2() {
List<String> names = employees.stream()
.map(Employee::getName)
.collect(Collectors.toList());
//.collect(Collectors.toCollection(LinkedList::new))
names.forEach(System.out::println);
}

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soo
lili
王萌
张帆
张帆
张帆
goog

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@Test
public void test5() {
Double avg = employees.stream()
.collect(Collectors.averagingDouble(Employee::getSalary));
System.out.println(avg);
}

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@Test
public void test() {
String collect = list.stream().collect(Collectors.joining(","));
System.out.println(collect);
}

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aaa,bbb,ccc,ddd,eee

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public class TestGroupBy {
private List<Detail> details = new ArrayList<>();
@Before
public void mock() {
details.add(new Detail(1, "001", "123456789", new BigDecimal("120.00")));
details.add(new Detail(2, "001", "123456789", new BigDecimal("99.32")));
details.add(new Detail(3, "003", "333222111", new BigDecimal("27.32")));
details.add(new Detail(4, "003", "333222111", new BigDecimal("36.00")));
details.add(new Detail(5, "003", "123456789", new BigDecimal("48.32")));
details.add(new Detail(6, "101", "123456789", new BigDecimal("53.32")));
details.add(new Detail(7, "101", "123456789", new BigDecimal("10.32")));
details.add(new Detail(8, "102", "333222111", new BigDecimal("3.32")));
details.add(new Detail(9, "103", "123456789", new BigDecimal("9.00")));
details.add(new Detail(10, "103", "123456789", new BigDecimal("12.12")));
}
@Test
public void test() {
Map<String, List<Detail>> groupByAir = details.parallelStream().collect(Collectors.groupingBy(Detail::getAir));
groupByAir.forEach((air, sameAirs) -> {
Map<String, List<Detail>> groupByDoc = sameAirs.parallelStream().collect(Collectors.groupingBy(Detail::getDocument));
groupByDoc.forEach((doc, sameDocs) -> {
Optional<BigDecimal> reduce = sameDocs.parallelStream().map(Detail::getPrice).reduce(BigDecimal::add);
reduce.ifPresent(e -> {
System.out.println(air + " "+ doc + " " + e);
});
});
});
}
@Data
@AllArgsConstructor
public static class Detail {
/**
* ID
*/
private Integer id;
/**
*航司编码
*/
private String air;
/**
*票号
*/
private String document;
/**
*机票价格
*/
private BigDecimal price;
}
}

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001 123456789 219.32
101 123456789 63.64
102 333222111 3.32
003 333222111 63.32
003 123456789 48.32
103 123456789 21.12

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@Test
public void test6() {
List<String> names = Arrays.asList("liuzijian", "liutongtong", "zhaoying", "wangwendi");
names.stream()
.filter(name -> name.startsWith("liu"))
.peek(name -> System.out.println("过滤后: " + name))
.map(String::toUpperCase)
.peek(name -> System.out.println("变成大写后: " + name))
.collect(Collectors.toList());
}

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过滤后: liuzijian
变成大写后: LIUZIJIAN
过滤后: liutongtong
变成大写后: LIUTONGTONG

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@Test
public void test() {
list.parallelStream().forEach(System.out::println);
}

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ccc
eee
ddd
bbb
aaa

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public static void main(String[] args) {
long reduce = LongStream.rangeClosed(0, 100000000000L)
.parallel() // 转换为并行流，底层是fork-join
.reduce(0, Long::sum);
System.out.println(reduce);
}

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package test.testinterface;
public interface MyInterface {
default String test() {
System.out.println("default");
return "default";
}
default void hello() {
System.out.println("my interface");
}
static void helloworld() {
System.out.println("hello java8!!!");
}
}

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package test.testinterface;
public class SubClass implements MyInterface {
public static void main(String[] args) {
SubClass subClass = new SubClass();
subClass.hello();
MyInterface.helloworld();
}
}

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my interface
hello java8!!!

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package test.testinterface;
public interface OtherInterface {
default void hello() {
System.out.println("other interface");
}
}

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package test.testinterface;
public class SubClass implements MyInterface, OtherInterface {
/**
* 多实现方法冲突，实现类必须实现
**/
@Override
public void hello() {
System.out.println("sub hello!");
}
public static void main(String[] args) {
SubClass subClass = new SubClass();
subClass.hello();
}
}

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package test.testinterface;
public class MyClass {
public String test() {
System.out.println("class");
return "class";
}
}

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package test.testinterface;
public class SubClass extends MyClass implements MyInterface, OtherInterface {
// 多实现方法冲突，实现类必须实现
@Override
public void hello() {
System.out.println("sub hello!");
}
public static void main(String[] args) {
SubClass subClass = new SubClass();
// 类优先原则，继承类的方法
subClass.test();
}
}

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package test.time;
import java.text.SimpleDateFormat;
public class Test1 {
public static void main(String[] args) {
SimpleDateFormat format = new SimpleDateFormat("yyyyMMdd");
Runnable r = new Runnable() {
@Override
public void run() {
try {
System.out.println(format.parse("20191231"));
} catch (Exception e) {
throw new RuntimeException(e);
}
}
};
for (int i=0; i<100; i++) {
new Thread(r, "t"+i).start();
}
}
}

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package test.time;
import java.text.SimpleDateFormat;
public class Test1 {
public static void main(String[] args) {
SimpleDateFormat format = new SimpleDateFormat("yyyyMMdd");
Runnable r = new Runnable() {
@Override
public void run() {
synchronized (format) {
try {
System.out.println(format.parse("20191231"));
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
};
for (int i=0; i<100; i++) {
new Thread(r, "t"+i).start();
}
}
}

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package test.time;
import java.text.SimpleDateFormat;
public class Test1 {
public static void main(String[] args) {
Runnable r = new Runnable() {
@Override
public void run() {
try {
System.out.println(new SimpleDateFormat("yyyyMMdd").parse("20191231"));
} catch (Exception e) {
throw new RuntimeException(e);
}
}
};
for (int i=0; i<100; i++) {
new Thread(r, "t"+i).start();
}
}
}

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package test.time;
import java.text.SimpleDateFormat;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class Test1 {
public static void main(String[] args) {
ExecutorService executorService = Executors.newFixedThreadPool(10);
ThreadLocal<SimpleDateFormat> threadLocal = ThreadLocal.withInitial(() -> new SimpleDateFormat("yyyyMMdd"));
Runnable runnable = new Runnable() {
@Override
public void run() {
try {
System.out.println(threadLocal.get().parse("20191231"));
}
catch (Exception e) {
throw new RuntimeException(e);
}
}
};
for (int i=0; i<100; i++) {
executorService.submit(runnable, "t"+i);
}
executorService.shutdown();
}
}

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package test.time;
import org.junit.Test;
import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.format.FormatStyle;
import java.time.temporal.*;
import java.util.Date;
public class Test4 {
/**
* java8 API获取当前时间
*/
@Test
public void current() {
Instant instant = Instant.now();
LocalDate localDate = LocalDate.now();
LocalTime localTime = LocalTime.now();
LocalDateTime localDateTime = LocalDateTime.now();
ZonedDateTime zonedDateTime = ZonedDateTime.now();
System.out.println(instant);
System.out.println(localDate);
System.out.println(localTime);
System.out.println(localDateTime);
System.out.println(zonedDateTime);
}
/**
* Instant的常见方法
*/
@Test
public void testInstant() {
//通过Instant获取当前时间戳，格林威治时间
Instant now = Instant.now();
System.out.println(now);
//添加时区，转换为带时区的时间：OffsetDateTime
OffsetDateTime us = now.atOffset(ZoneOffset.ofHours(-4));
System.out.println(us);//US
//设置偏移量
OffsetDateTime offsetDateTime = now.atOffset(ZoneOffset.ofHours(+8));
System.out.println(offsetDateTime);//CN
System.out.println(now.atOffset(ZoneOffset.ofHours(+9)));//JP
System.out.println(now.atOffset(ZoneOffset.ofHours(+10)));//AU
//根据给定的Unix时间戳（即自1970年1月1日00:00:00 UTC起的秒数）创建一个Instant对象
Instant instant = Instant.ofEpochSecond(1);//开始于1970
System.out.println(instant);
//设置时区
ZonedDateTime zonedDateTime = now.atZone(ZoneId.of("GMT+9"));
LocalDateTime localDateTime = zonedDateTime.toLocalDateTime();
System.out.println(localDateTime);
}
/**
* LocalDateTime LocalDate LocalTime 的常见方法和使用
*/
@Test
public void testLocalDateTime() {
// 获取当前时间
LocalDateTime now = LocalDateTime.now();
System.out.println(now);
//构造时间
LocalDateTime localDateTime = LocalDateTime.of(2019,8,8,12,23,50);
System.out.println(localDateTime);
//从LocalDate和LocalTime构造时间
System.out.println(LocalDateTime.of(LocalDate.now(), LocalTime.now()));
// 获取年月日时分秒
System.out.println(localDateTime.getYear());
System.out.println(localDateTime.getDayOfYear());
System.out.println(localDateTime.getDayOfMonth());
//星期
DayOfWeek dayOfWeek = localDateTime.getDayOfWeek();
System.out.println(dayOfWeek);
//当前时间的纳秒部分，表示这个时间点内的精细时间
System.out.println(localDateTime.getNano());
//时间计算
System.out.println(LocalDateTime.now().plusMonths(2));
System.out.println(LocalDateTime.now().minusYears(2));
System.out.println(LocalDateTime.now().plusHours(24));
System.out.println(LocalDateTime.now().plusNanos(500));
System.out.println(LocalDateTime.now().plusYears(2).plusMonths(8).plusDays(9));
// Period.of 用于创建一个表示特定时间间隔的Period对象
System.out.println(LocalDateTime.now().plus(Period.of(3, 5, 20))); ;
// ChronoUnit.DECADES代表十年
System.out.println(LocalDateTime.now().plus(3, ChronoUnit.DECADES)) ;
// 时间修改
System.out.println(LocalDateTime.now().withMonth(2));
System.out.println(LocalDateTime.now().withDayOfMonth(25));
System.out.println(LocalDateTime.now().withSecond(22));
System.out.println(LocalDateTime.now().with(ChronoField.DAY_OF_MONTH, 2));
System.out.println(LocalDateTime.now().with(ChronoField.MONTH_OF_YEAR, 8));
// LocalDate LocalTime
System.out.println(LocalDate.of(2020, 1, 19));
System.out.println(LocalDate.of(2020, Month.AUGUST, 19));
System.out.println(LocalDate.of(2020, Month.of(12), 19));
System.out.println(LocalTime.of(20, 0));
System.out.println(LocalDate.now().withMonth(8));
System.out.println(LocalDate.of(2020, Month.AUGUST, 19).plusDays(5));
System.out.println(LocalDate.of(2020, Month.of(12), 19));
System.out.println( LocalTime.of(20, 0).plusHours(8) );
// LocalDate的方法，判断当前年份是否为闰年
System.out.println(LocalDate.now().isLeapYear());
}
/**
* TemporalAdjusters 时间校正器
*/
@Test
public void testTemporalAdjusters() {
// 下一个周四
LocalDateTime dateTime = LocalDateTime.now();
dateTime.with(TemporalAdjusters.next(DayOfWeek.THURSDAY));
System.out.println(dateTime);
dateTime.with(TemporalAdjusters.previous(DayOfWeek.THURSDAY));
System.out.println(dateTime);
dateTime.with(TemporalAdjusters.nextOrSame(DayOfWeek.THURSDAY));
System.out.println(dateTime);
dateTime.with(TemporalAdjusters.previousOrSame(DayOfWeek.THURSDAY));
System.out.println(dateTime);
System.out.println(LocalDate.now().with(TemporalAdjusters.nextOrSame(DayOfWeek.SATURDAY)));
// 获取月份第一天
System.out.println(LocalDate.now().with(TemporalAdjusters.firstDayOfMonth()));
System.out.println(LocalDate.now().with(TemporalAdjusters.firstDayOfNextMonth()));
// 自定义计算下一个工作日
LocalDateTime nextWorkDay = LocalDateTime.now().with((e) -> {
LocalDateTime temp = LocalDateTime.from(e);
DayOfWeek dayOfWeek = temp.getDayOfWeek();
if (dayOfWeek.equals(DayOfWeek.FRIDAY)) {
return temp.plusDays(3);
} else if (dayOfWeek.equals(DayOfWeek.SATURDAY)) {
return temp.plusDays(2);
} else {
return temp.plusDays(1);
}
});
System.out.println(nextWorkDay);
}
public void test() {
System.out.println(Year.now());
System.out.println(YearMonth.now());
System.out.println(MonthDay.now());
}
/**
* 计算时间间隔：武汉封了多少天，多少小时
*/
@Test
public void testChronoUnit() {
LocalDateTime from = LocalDateTime.of(2020, Month.JANUARY, 23, 10, 0,0);
LocalDateTime to = LocalDateTime.of(2020, Month.APRIL, 8, 0, 0,0);
long days = ChronoUnit.DAYS.between(from, to);
long hours = ChronoUnit.HOURS.between(from, to);
System.out.println( days );
System.out.println( hours );
}
/**
* 使用 TemporalQuery 来计算当前时间与一个指定时间点（2020年1月19日10:00:00）之间的小时差，
* 并将其作为 long 类型的值返回
*/
@Test
public void testTemporalQuery() {
long l = LocalDateTime.now().query(new TemporalQuery<Long>() {
@Override
public Long queryFrom(TemporalAccessor temporal) {
LocalDateTime now = LocalDateTime.from(temporal);
LocalDateTime from = LocalDateTime.of(2020, Month.JANUARY, 19, 10, 0,0);
return ChronoUnit.HOURS.between(from, now);
}
});
System.out.println(l);
}
/**
* Duration类，只能计算时间差异
*/
@Test
public void testDurationPeriod() {
LocalTime start = LocalTime.of(20, 0);
LocalTime end = LocalTime.of(21, 30);
// 时间间隔
Duration between = Duration.between(start, end);
System.out.println(between.toHours());
System.out.println(between.toMinutes());
}
/**
* 格式化 DateTimeFormatter
*/
@Test
public void testDateTimeFormatter() {
DateTimeFormatter formatter = DateTimeFormatter.ISO_DATE_TIME;
System.out.println(LocalDateTime.now().format(formatter));
LocalDate localDate = LocalDate.parse("2009-12-31", DateTimeFormatter.ofPattern("yyyy-MM-dd"));
System.out.println(localDate);
LocalDateTime localDateTime = LocalDateTime.parse("2009-12-31 01:01:02", DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
System.out.println(localDateTime);
// 2024年12月1日星期日
System.out.println(LocalDateTime.now().format(DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL)));
// 2024年12月1日
System.out.println(LocalDateTime.now().format(DateTimeFormatter.ofLocalizedDate(FormatStyle.LONG)));
// 24-12-1
System.out.println(LocalDateTime.now().format(DateTimeFormatter.ofLocalizedDate(FormatStyle.SHORT)));
// 2024-12-1
System.out.println(LocalDateTime.now().format(DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM)));
}
@Test
public void getAvailableZoneIds() {
// 当前系统时区
System.out.println(ZoneId.systemDefault());
// 打印java8中所有支持时区
ZoneId.getAvailableZoneIds().forEach(System.out::println);
}
/**
* OffsetDateTime
*/
@Test
public void testOffsetDateTime() {
OffsetDateTime offsetDateTime = new Date().toInstant().atOffset(ZoneOffset.of("-4"));
System.out.println(offsetDateTime);
System.out.println(offsetDateTime.toLocalDateTime());
OffsetDateTime of = OffsetDateTime.of(LocalDateTime.now(), ZoneOffset.of("-4"));
System.out.println(of);
}
/**
* ZonedDateTime
*/
@Test
public void testZonedDateTime() {
// 当前时间转换为东京时间是几时
ZonedDateTime zonedDateTime = ZonedDateTime.now(ZoneId.of("Asia/Tokyo"));
System.out.println(zonedDateTime);
System.out.println(zonedDateTime.toLocalDateTime());
ZonedDateTime of = ZonedDateTime.of(LocalDateTime.now(), ZoneId.of("Asia/Tokyo"));
System.out.println(of);
// 为当前时间带上时区
ZonedDateTime tokyo = LocalDateTime.now().atZone(ZoneId.of("Asia/Tokyo"));
System.out.println(tokyo);
System.out.println(tokyo.toLocalDateTime());
// 将一个时区时间转换为同一时刻另一个时区时间
ZonedDateTime beijing = tokyo.withZoneSameInstant(ZoneId.of("GMT+8"));
System.out.println(beijing);
ZonedDateTime usa = LocalDateTime.now()
.atZone(ZoneId.systemDefault())
.withZoneSameInstant(ZoneId.of("GMT-4"));
System.out.println(usa);
}
}

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package test.time;
import org.junit.Test;
import java.sql.Timestamp;
import java.time.*;
import java.util.Calendar;
import java.util.Date;
public class Test5 {
/**
* 将 LocalDateTime 和系统默认时区结合，转换为 ZonedDateTime
* 再将 ZonedDateTime 转换为 Instant，这是一个包含 UTC 时间戳的对象。
* Date.from()：将 Instant 转换为 java.util.Date 对象
*/
@Test
public void toDate() {
LocalDateTime localDateTime = LocalDateTime.now();
Instant instant = localDateTime.atZone(ZoneId.systemDefault()).toInstant();
Date date = Date.from(instant);
System.out.println(date);
}
@Test
public void toLocalDateTime() {
Date date = new Date();
LocalDateTime dateTime = LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault());
System.out.println(dateTime);
}
/**
* java.sql.Date 转换 LocalDateTime
*/
@Test
public void sqlDate() {
java.sql.Date date = new java.sql.Date(System.currentTimeMillis());
LocalDate localDate = date.toLocalDate();
System.out.println(localDate);
Timestamp timestamp = new Timestamp(System.currentTimeMillis());
LocalDateTime localDateTime = timestamp.toLocalDateTime();
System.out.println(localDateTime);
}
/**
* Calendar 转换 LocalDateTime
*/
@Test
public void calendarToLocalDateTime() {
Calendar calendar = Calendar.getInstance();
ZonedDateTime zonedDateTime = ZonedDateTime.ofInstant(calendar.toInstant(), calendar.getTimeZone().toZoneId());
System.out.println(zonedDateTime.toLocalDateTime());
}
}

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Optional<String> optional = Optional.of("Hello, World!");

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Optional<String> optional = Optional.ofNullable(null);

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