Java语言特性系列
- Java5的新特性
- Java6的新特性
- Java7的新特性
- Java8的新特性
- Java9的新特性
- Java10的新特性
- Java11的新特性
序
本文主要讲述一下Java10的新特性
特性列表
- 286: Local-Variable Type Inference(
重磅)
相关解读: java10系列(二)Local-Variable Type Inference
- 296: Consolidate the JDK Forest into a Single Repository
- 304: Garbage-Collector Interface
- 307: Parallel Full GC for G1
- 310: Application Class-Data Sharing
- 312: Thread-Local Handshakes
- 313: Remove the Native-Header Generation Tool (javah)
- 314: Additional Unicode Language-Tag Extensions
- 316: Heap Allocation on Alternative Memory Devices
- 317: Experimental Java-Based JIT Compiler(
重磅)
相关解读: Java10来了，来看看它一同发布的全新JIT编译器
- 319: Root Certificates
相关解读: OpenJDK 10 Now Includes Root CA Certificates
- 322: Time-Based Release Versioning
相关解读: java10系列(一)Time-Based Release Versioning
细项解读
上面列出的是大方面的特性，除此之外还有一些api的更新及废弃，主要见What's New in JDK 10 - New Features and Enhancements，这里举几个例子。
Optional.orElseThrow()
/Library/Java/JavaVirtualMachines/jdk-10.jdk/Contents/Home/lib/src.zip!/java.base/java/util/Optional.java
- 源码
/**
* If a value is present, returns the value, otherwise throws
* {@code NoSuchElementException}.
*
* @return the non-{@code null} value described by this {@code Optional}
* @throws NoSuchElementException if no value is present
* @since 10
*/
public T orElseThrow() {
if (value == null) {
throw new NoSuchElementException("No value present");
}
return value;
}
- 实例
@Test
public void testOrElseThrow(){
var data = List.of("a","b","c");
Optional optional = data.stream()
.filter(s -> s.startsWith("z"))
.findAny();
String res = optional.orElseThrow();
System.out.println(res);
}
新增了orElseThrow与get相对应
输出
java.util.NoSuchElementException: No value present
at java.base/java.util.Optional.orElseThrow(Optional.java:371)
at com.example.FeatureTest.testOrElseThrow(FeatureTest.java:19)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
APIs for Creating Unmodifiable Collections
java9新增的of工厂方法的接口参数是一个个元素，java10新增List.copyOf, Set.copyOf,及Map.copyOf用来从已有集合创建ImmutableCollections
- List.copyOf源码
/**
* Returns an unmodifiable List containing the elements of
* the given Collection, in its iteration order. The given Collection must not be null,
* and it must not contain any null elements. If the given Collection is subsequently
* modified, the returned List will not reflect such modifications.
*
* @implNote
* If the given Collection is an unmodifiable List,
* calling copyOf will generally not create a copy.
*
* @param the {@code List}'s element type
* @param coll a {@code Collection} from which elements are drawn, must be non-null
* @return a {@code List} containing the elements of the given {@code Collection}
* @throws NullPointerException if coll is null, or if it contains any nulls
* @since 10
*/
@SuppressWarnings("unchecked")
static List copyOf(Collection coll) {
if (coll instanceof ImmutableCollections.AbstractImmutableList) {
return (List)coll;
} else {
return (List)List.of(coll.toArray());
}
}
- 实例
@Test(expected = UnsupportedOperationException.class)
public void testCollectionCopyOf(){
List list = IntStream.rangeClosed(1,10)
.mapToObj(i -> "num"+i)
.collect(Collectors.toList());
List newList = List.copyOf(list);
newList.add("not allowed");
}
Collectors新增了toUnmodifiableList, toUnmodifiableSet,以及 toUnmodifiableMap方法
@Test(expected = UnsupportedOperationException.class)
public void testCollectionCopyOf(){
List list = IntStream.rangeClosed(1,10)
.mapToObj(i -> "num"+i)
.collect(Collectors.toUnmodifiableList());
list.add("not allowed");
}
小结
java10最主要的新特性，在语法层面就属于Local-Variable Type Inference，而在jvm方面307: Parallel Full GC for G1以及317: Experimental Java-Based JIT Compiler都比较重磅，值得深入研究。
doc
- JDK 10 Features
- Introducing Java SE 10(
官方解读) - What's New in JDK 10 - New Features and Enhancements(
官方细项解读) - JDK-8140281 : (opt) add no-arg orElseThrow() as preferred alternative to get()
- JDK-8177290 : add copy factory methods for unmodifiable List, Set, Map