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
• @L_360_15@
• 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<String> 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 <a href="#unmodifiable">unmodifiable List</a> 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 <a href="#unmodifiable">unmodifiable List</a>,      * calling copyOf will generally not create a copy.      *      * @param <E> 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 <E> List<E> copyOf(Collection<? extends E> coll) {         if (coll instanceof ImmutableCollections.AbstractImmutableList) {             return (List<E>)coll;         } else {             return (List<E>)List.of(coll.toArray());         }     }

• 实例

    @Test(expected = UnsupportedOperationException.class)     public void testCollectionCopyOf(){         List<String> list = IntStream.rangeClosed(1,10)                 .mapToObj(i -> "num"+i)                 .collect(Collectors.toList());         List<String> 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<String> 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