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Welcome to the JAVA foundation course
Blog address: https://segmentfault.com/a/1190000019686260
This series of articles will mainly explain some of the basics for JAVA point, usually summarized as summarized, whether it is new to JAVA development industry veteran or rookie, hope the majority peer bring some help. If you have questions please leave a message or add QQ: 243042162.
Message:
Everyone has potential energy, but can easily be used to cover up, to be blurred by time, by laziness.
Ten new features
1.Lambda expression
public class JDK8_features {
public List<Integer> list = Lists.newArrayList(1,2,3,4,5,6,7,8,9,10);
/**
* 1.Lambda表达式
*/
@Test
public void testLambda(){
list.forEach(System.out::println);
list.forEach(e -> System.out.println("方式二："+e));
}
}
2.Stream functional elements of the set operational flow
/**
* 2.Stream函数式操作流元素集合
*/
@Test
public void testStream(){
List<Integer> nums = Lists.newArrayList(1,1,null,2,3,4,null,5,6,7,8,9,10);
System.out.println("求和："+nums
.stream()//转成Stream
.filter(team -> team!=null)//过滤
.distinct()//去重
.mapToInt(num->num*2)//map操作
.skip(2)//跳过前2个元素
.limit(4)//限制取前4个元素
.peek(System.out::println)//流式处理对象函数
.sum());//
}
3. New Interface: The default method, and static methods
/**
* 3.接口新增：默认方法与静态方法
* default 接口默认实现方法是为了让集合类默认实现这些函数式处理，而不用修改现有代码
* （List继承于Iterable<T>，接口默认方法不必须实现default forEach方法）
*/
@Test
public void testDefaultFunctionInterface(){
//可以直接使用接口名.静态方法来访问接口中的静态方法
JDK8Interface1.staticMethod();
//接口中的默认方法必须通过它的实现类来调用
new JDK8InterfaceImpl1().defaultMethod();
//多实现类，默认方法重名时必须复写
new JDK8InterfaceImpl2().defaultMethod();
}
public class JDK8InterfaceImpl1 implements JDK8Interface1 {
//实现接口后，因为默认方法不是抽象方法，重写/不重写都成！
// @Override
// public void defaultMethod(){
// System.out.println("接口中的默认方法");
// }
}
public class JDK8InterfaceImpl2 implements JDK8Interface1,JDK8Interface2 {
//实现接口后，默认方法名相同，必须复写默认方法
@Override
public void defaultMethod() {
//接口的
JDK8Interface1.super.defaultMethod();
System.out.println("实现类复写重名默认方法！！！！");
}
}
4. The method references, and Lambda used in combination
@Test
public void testMethodReference(){
//构造器引用。语法是Class::new，或者更一般的Class< T >::new，要求构造器方法是没有参数；
final Car car = Car.create( Car::new );
final List< Car > cars = Arrays.asList( car );
//静态方法引用。语法是Class::static_method，要求接受一个Class类型的参数；
cars.forEach( Car::collide );
//任意对象的方法引用。它的语法是Class::method。无参，所有元素调用；
cars.forEach( Car::repair );
//特定对象的方法引用，它的语法是instance::method。有参，在某个对象上调用方法，将列表元素作为参数传入；
final Car police = Car.create( Car::new );
cars.forEach( police::follow );
}
public static class Car {
public static Car create( final Supplier< Car > supplier ) {
return supplier.get();
}
public static void collide( final Car car ) {
System.out.println( "静态方法引用 " + car.toString() );
}
public void repair() {
System.out.println( "任意对象的方法引用 " + this.toString() );
}
public void follow( final Car car ) {
System.out.println( "特定对象的方法引用 " + car.toString() );
}
}
5. Repeat introduced annotations
@Test
public void RepeatingAnnotations(){
RepeatingAnnotations.main(null);
}
6. Type Notes
@Test
public void ElementType(){
Annotations.main(null);
}
7. date Date / Time API (JSR 310)
@Test
public void DateTime(){
//1.Clock
final Clock clock = Clock.systemUTC();
System.out.println( clock.instant() );
System.out.println( clock.millis() );
//2. ISO-8601格式且无时区信息的日期部分
final LocalDate date = LocalDate.now();
final LocalDate dateFromClock = LocalDate.now( clock );
System.out.println( date );
System.out.println( dateFromClock );
// ISO-8601格式且无时区信息的时间部分
final LocalTime time = LocalTime.now();
final LocalTime timeFromClock = LocalTime.now( clock );
System.out.println( time );
System.out.println( timeFromClock );
// 3.ISO-8601格式无时区信息的日期与时间
final LocalDateTime datetime = LocalDateTime.now();
final LocalDateTime datetimeFromClock = LocalDateTime.now( clock );
System.out.println( datetime );
System.out.println( datetimeFromClock );
// 4.特定时区的日期/时间，
final ZonedDateTime zonedDatetime = ZonedDateTime.now();
final ZonedDateTime zonedDatetimeFromClock = ZonedDateTime.now( clock );
final ZonedDateTime zonedDatetimeFromZone = ZonedDateTime.now( ZoneId.of( "America/Los_Angeles" ) );
System.out.println( zonedDatetime );
System.out.println( zonedDatetimeFromClock );
System.out.println( zonedDatetimeFromZone );
//5.在秒与纳秒级别上的一段时间
final LocalDateTime from = LocalDateTime.of( 2014, Month.APRIL, 16, 0, 0, 0 );
final LocalDateTime to = LocalDateTime.of( 2015, Month.APRIL, 16, 23, 59, 59 );
final Duration duration = Duration.between( from, to );
System.out.println( "Duration in days: " + duration.toDays() );
System.out.println( "Duration in hours: " + duration.toHours() );
}
8. Added base64 encryption and decryption API
@Test
public void testBase64(){
final String text = "就是要测试加解密！！abjdkhdkuasu!!@@@@";
String encoded = Base64.getEncoder()
.encodeToString( text.getBytes( StandardCharsets.UTF_8 ) );
System.out.println("加密后="+ encoded );
final String decoded = new String(
Base64.getDecoder().decode( encoded ),
StandardCharsets.UTF_8 );
System.out.println( "解密后="+decoded );
}
9. Parallel Array (Parallel) Operation
@Test
public void testParallel(){
long[] arrayOfLong = new long [ 20000 ];
//1.给数组随机赋值
Arrays.parallelSetAll( arrayOfLong,
index -> ThreadLocalRandom.current().nextInt( 1000000 ) );
//2.打印出前10个元素
Arrays.stream( arrayOfLong ).limit( 10 ).forEach(
i -> System.out.print( i + " " ) );
System.out.println();
//3.数组排序
Arrays.parallelSort( arrayOfLong );
//4.打印排序后的前10个元素
Arrays.stream( arrayOfLong ).limit( 10 ).forEach(
i -> System.out.print( i + " " ) );
System.out.println();
}
10.JVM PermGen the space is removed: it is substituted Metaspace (JEP 122) metaSpace
@Test
public void testMetaspace(){
//-XX:MetaspaceSize初始空间大小，达到该值就会触发垃圾收集进行类型卸载，同时GC会对该值进行调整
//-XX:MaxMetaspaceSize最大空间，默认是没有限制
//-XX:MinMetaspaceFreeRatio在GC之后，最小的Metaspace剩余空间容量的百分比，减少为分配空间所导致的垃圾收集
//-XX:MaxMetaspaceFreeRatio在GC之后，最大的Metaspace剩余空间容量的百分比，减少为释放空间所导致的垃圾收集
}
Reference website:
(1) https://www.cnblogs.com/suger43894/p/8746514.html
(2) https://blog.csdn.net/xuspcsdn/article/details/87917592