JShell
交互式执行java代码
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| jshell> int a=10
a ==> 10
jshell> a*7+5
$30 ==> 75
jshell> System.out.println("hello")
hello
jshell> void method(int x, int y) {
...> System.out.println(x+y);
...> }
| 已修改 方法 method(int,int)
jshell> method(10,20);
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|
不可变List, Set, Map
Immutable List
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| jshell> List l = List.of(1,2,3);
l ==> [1, 2, 3]
jshell> l.add(4);
| 警告:
| 对作为原始类型java.util.List的成员的add(E)的调用未经过检查
| l.add(4);
| ^------^
| java.lang.UnsupportedOperationException thrown:
| at ImmutableCollections.uoe (ImmutableCollections.java:71)
| at ImmutableCollections$AbstractImmutableList.add (ImmutableCollections.java:77)
| at (#36:1)
|
Immutable Set
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| jshell> Set set = Set.of(1,2,3);
set ==> [1, 3, 2]
jshell> set.add(4);
| 警告:
| 对作为原始类型java.util.Set的成员的add(E)的调用未经过检查
| set.add(4);
| ^--------^
| java.lang.UnsupportedOperationException thrown:
| at ImmutableCollections.uoe (ImmutableCollections.java:71)
| at ImmutableCollections$AbstractImmutableSet.add (ImmutableCollections.java:281)
| at (#38:1)
|
Immutable Map
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| jshell> Map.of()
$39 ==> {}
jshell> Map map = Map.of(1, "a", 2, "b", 3, "c");
map ==> {1=a, 3=c, 2=b}
jshell> map.put(4, "d");
| 警告:
| 对作为原始类型java.util.Map的成员的put(K,V)的调用未经过检查
| map.put(4, "d");
| ^-------------^
| java.lang.UnsupportedOperationException thrown:
| at ImmutableCollections.uoe (ImmutableCollections.java:71)
| at ImmutableCollections$AbstractImmutableMap.put (ImmutableCollections.java:558)
| at (#41:1)
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接口私有方法 Private Method in interface
com.interfaces.PrivateMethod
模块化 Module System
- com.hello
- com.hello.client
Process API
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| jshell> ProcessHandle currentProcess = ProcessHandle.current();
currentProcess ==> 3214
jshell> System.out.println("Current Process Id: = " + currentProcess.pid());
Current Process Id: = 3214
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资源对象的try/catch
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| jshell> void tryResource() throws IOException {
...> BufferedReader reader1 = new BufferedReader(new FileReader("/tmp/a.txt"));
...> try (reader1) {
...> System.out.println(reader1.readLine());
...> }
...> }
| 已修改 方法 tryResource()
|
Stream api improvements
com.stream.StreamTest
optional
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| jshell> Optional.of(1)
$46 ==> Optional[1]
jshell> Optional.empty();
$47 ==> Optional.empty
jshell> Optional.of(1).ifPresentOrElse(x -> System.out.println("get:" + x), () -> System.out.println("cannot get"))
get:1
jshell> Optional.empty().ifPresentOrElse(x -> System.out.println("get:" + x), () -> System.out.println("cannot get"))
cannot get
jshell> Optional.empty().or(() -> Optional.of(2))
$50 ==> Optional[2]
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HTTP 2 Client API
api改进
支持web socket 等
GC
- CMS垃圾回收算法不再推荐使用; 推荐性能更好的G1算法
- GC算法之间的绑定关系被取消
other
java docs改进
源代码
本文全部源代码：https://github.com/wangsaisai/java-9-tutorial.git