jdk11

今天(2018-09-26), 期待的重量级更新jdk11正式版发布

可以通过jdk11 下载

Feature

Local Variable Type Inference

在以前对变量进行声明时

String text = "你好 Jdk 11"

目前可以通过var 关键字进行声明

var text = "你好 Jdk 11"

如果声明的是一个常量

final var text = "你好 Jdk 11"

而不是scala 那样

val text = "你好 Jdk 11"

Collections

List, Set, Map 扩展了of, copyOf 方法

var list = List.of("a", "b", "c")
var copy = List.copyOf(list)
System.out.println(list == copy) // true

var map = Map.of("A", "B", "B", "c", "C", "D");

var copyMap = Map.copyOf(map);

System.out.println(copyMap == map);

var set = Set.of("A", "B", "C");

var copySet = Set.copyOf(set);

System.out.println(copySet == set);

of 方法构建的是一个immutable 集合

如果使用的是通过直接new 的方式，那么集合不再是一个immutable 集合，而是一个mutable 集合

那么通过copyOf方法得到一个copy , 然后执行比较的话，结果为false

var mutableSet = new HashSet<String>();

var copyMutableSet = Set.copyOf(mutableSet);

System.out.println(copyMutableSet == mutableSet);

var mutableList = new ArrayList<Integer>();

mutableList.add(1);
mutableList.add(2);
mutableList.add(3);

var copyMutableList = List.copyOf(mutableList);

System.out.println(mutableList == copyMutableList);

var mutableMap = new HashMap<String, Integer>();

mutableMap.put("A", 1);
mutableMap.put("B", 2);
mutableMap.put("C", 3);

var copyMutableMap = Map.copyOf(mutableMap);

System.out.println(copyMutableMap == mutableMap);

Stream

ofNullable method

Stream 添加了ofNullable 方法

Stream.ofNullable(null).count()

Stream.dropWhile method

Stream.of(1,2,3,2,1)
.dropWhile(n -> n < 3)
.collect(Collector.toList());

Stream.takeWhile method

Stream.of(1,2,3,2,1)
.takeWhile(n -> n < 3)
.collect(Collector.toList())

Optionals

var foo = Optional.of("foo").orElseThrow();
var count = Optional.of("foo").stream().count();

System.out.println(foo);
System.out.println(count);

var op = Optional.ofNullable(null).or(() -> Optional.of("fallback")).get();

System.out.println(op);

Strings

String 类有更多的快捷方法

var foo = Optional.of("foo").orElseThrow();
var count = Optional.of("foo").stream().count();

System.out.println(foo);
System.out.println(count);

var op = Optional.ofNullable(null).or(() -> Optional.of("fallback")).get();

System.out.println(op);

InputStream

InputStream 添加了一个便捷的transferTo方法

var classLoader = ClassLoader.getSystemClassLoader();

var inputStream = classLoader.getResourceAsStream("myfile.txt");

var tempFile = File.createTempFile("myFileCopy", "txt");

try(var outputStrema = new FileOutputStream(tempFile)){
    inputStream.transferTo(outputStrema);
}

当然最重要的还是关于ZGC的开启并可用

github