Java 13 It has been officially released on September 17, 2019, Download Java 13 here Or here openJDK archived .
Java 13 features.
- JEP 350: dynamic CDS Archive
- JEP 351: ZGC: uncommit unused memory
- JEP 353: re implement the old socket API
- JEP 354: switch expression (Preview) (developer functions)
- JEP 355: text block (Preview) (developer functions)
JEP 350 dynamic CDS Archive
Java 10 introduces JEP 310 Application Class-Data Sharing . The JEP simplifies the process of creating CDS archives.
This command creates a CDS archive of. jar.
$ java -XX:ArchiveClassesAtExit=hello.jsa -cp hello.jar Hello
This command runs. jar using an existing CDS archive.
$ bin/java -XX:SharedArchiveFile=hello.jsa -cp hello.jar Hello
Class data sharing (CDS) improves startup performance by creating one class data archive at a time and reusing it so that the JVM does not have to create it again.
Please read the following articles to learn more about CDS:
JEP 351 ZGC: uncommission unused memory
Java 11 introduced JEP 333: Z garbage collector (experimental) ; provides a short pause time when cleaning up heap memory. However, even if it is not used for a long time, it will not return unused heap memory to the operating system.
The JEP enhances ZGC by returning unused heap memory to the operating system.
JEP-353 re implements the old socket API
java.net.Socket and java.net.ServerSocket The basic implementation of JDK 1.0 can be traced back to JDK 1.0, which is a combination of legacy Java and C code that is difficult to maintain and debug. This JEP introduces a new basic implementation for the Socket API, which is the default implementation in Java 13.
Before Java 13, it used PlainSocketImpl for SocketImpl
public class ServerSocket implements java.io.Closeable {
/**
* The implementation of this Socket.
*/
private SocketImpl impl;
}Java 13 introduces a new NioSocketImpl class to replace PlainSocketImpl. However, if there is a problem, we can still set the jdk.net.usePlainSocketImpl System properties to switch back to the old implementation PlainSocketImpl.
See a simple Socket example.
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
public class JEP353 {
public static void main(String[] args) {
try (ServerSocket serverSocket = new ServerSocket(8888)){
boolean running = true;
while(running){
Socket clientSocket = serverSocket.accept();
//do something with clientSocket
}
} catch (IOException e) {
e.printStackTrace();
}
}
}In Java 13, the default implementation is NioSocketImpl
D:\test>javac JEP353.java D:\test>java JEP353 D:\test>java -XX:+TraceClassLoading JEP353 | findStr Socket [0.040s][info ][class,load] java.net.ServerSocket source: jrt:/java.base [0.040s][info ][class,load] jdk.internal.access.JavaNetSocketAccess source: jrt:/java.base [0.040s][info ][class,load] java.net.ServerSocket$1 source: jrt:/java.base [0.040s][info ][class,load] java.net.SocketOptions source: jrt:/java.base [0.040s][info ][class,load] java.net.SocketImpl source: jrt:/java.base [0.044s][info ][class,load] java.net.SocketImpl$$Lambda$1/0x0000000800ba0840 source: java.net.SocketImpl [0.047s][info ][class,load] sun.net.PlatformSocketImpl source: jrt:/java.base [0.047s][info ][class,load] sun.nio.ch.NioSocketImpl source: jrt:/java.base [0.047s][info ][class,load] sun.nio.ch.SocketDispatcher source: jrt:/java.base [0.052s][info ][class,load] java.net.SocketAddress source: jrt:/java.base [0.052s][info ][class,load] java.net.InetSocketAddress source: jrt:/java.base [0.052s][info ][class,load] java.net.InetSocketAddress$InetSocketAddressHolder source: jrt:/java.base [0.053s][info ][class,load] sun.net.ext.ExtendedSocketOptions source: jrt:/java.base [0.053s][info ][class,load] jdk.net.ExtendedSocketOptions source: jrt:/jdk.net [0.053s][info ][class,load] java.net.SocketOption source: jrt:/java.base [0.053s][info ][class,load] jdk.net.ExtendedSocketOptions$ExtSocketOption source: jrt:/jdk.net [0.053s][info ][class,load] jdk.net.SocketFlow source: jrt:/jdk.net [0.053s][info ][class,load] jdk.net.ExtendedSocketOptions$PlatformSocketOptions source: jrt:/jdk.net [0.053s][info ][class,load] jdk.net.ExtendedSocketOptions$PlatformSocketOptions$1 source: jrt:/jdk.net [0.054s][info ][class,load] jdk.net.ExtendedSocketOptions$1 source: jrt:/jdk.net [0.054s][info ][class,load] sun.nio.ch.NioSocketImpl$FileDescriptorCloser source: jrt:/java.base [0.055s][info ][class,load] java.net.Socket source: jrt:/java.base
We can set Djdk.net.usePlainSocketImpl System properties to switch back to PlainSocketImpl.
D:\test>java -Djdk.net.usePlainSocketImpl -XX:+TraceClassLoading JEP353 | findStr Socket [0.041s][info ][class,load] java.net.ServerSocket source: jrt:/java.base [0.041s][info ][class,load] jdk.internal.access.JavaNetSocketAccess source: jrt:/java.base [0.041s][info ][class,load] java.net.ServerSocket$1 source: jrt:/java.base [0.041s][info ][class,load] java.net.SocketOptions source: jrt:/java.base [0.041s][info ][class,load] java.net.SocketImpl source: jrt:/java.base [0.045s][info ][class,load] java.net.SocketImpl$$Lambda$1/0x0000000800ba0840 source: java.net.SocketImpl [0.048s][info ][class,load] sun.net.PlatformSocketImpl source: jrt:/java.base [0.048s][info ][class,load] java.net.AbstractPlainSocketImpl source: jrt:/java.base [0.048s][info ][class,load] java.net.PlainSocketImpl source: jrt:/java.base [0.048s][info ][class,load] java.net.AbstractPlainSocketImpl$1 source: jrt:/java.base [0.050s][info ][class,load] sun.net.ext.ExtendedSocketOptions source: jrt:/java.base [0.050s][info ][class,load] jdk.net.ExtendedSocketOptions source: jrt:/jdk.net [0.050s][info ][class,load] java.net.SocketOption source: jrt:/java.base [0.051s][info ][class,load] jdk.net.ExtendedSocketOptions$ExtSocketOption source: jrt:/jdk.net [0.051s][info ][class,load] jdk.net.SocketFlow source: jrt:/jdk.net [0.051s][info ][class,load] jdk.net.ExtendedSocketOptions$PlatformSocketOptions source: jrt:/jdk.net [0.051s][info ][class,load] jdk.net.ExtendedSocketOptions$PlatformSocketOptions$1 source: jrt:/jdk.net [0.051s][info ][class,load] jdk.net.ExtendedSocketOptions$1 source: jrt:/jdk.net [0.051s][info ][class,load] java.net.StandardSocketOptions source: jrt:/java.base [0.051s][info ][class,load] java.net.StandardSocketOptions$StdSocketOption source: jrt:/java.base [0.053s][info ][class,load] sun.net.ext.ExtendedSocketOptions$$Lambda$2/0x0000000800ba1040 source: sun.net.ext.ExtendedSocketOptions [0.056s][info ][class,load] java.net.SocketAddress source: jrt:/java.base [0.056s][info ][class,load] java.net.InetSocketAddress source: jrt:/java.base [0.058s][info ][class,load] java.net.InetSocketAddress$InetSocketAddressHolder source: jrt:/java.base [0.059s][info ][class,load] java.net.SocketCleanable source: jrt:/java.base
JEP-354 switch expression (Preview)
Java 12 introduces JEP 325 Switch expression . Instead of breaking value, the JEP uses the yield keyword to return a value from the switch expression.
PS this is the preview language function in Java 13
In the traditional switch statement, we can return the following values:
private static String getNumber(int number) {
String result = "";
switch (number) {
case 1:
case 2:
result = "one or two";
break;
case 3:
result = "three";
break;
case 4:
case 5:
case 6:
result = "four or five or six";
break;
default:
result = "unknown";
}
;
return result;
}In Java 12, we can use break to return a value from switch.
private static String getNumberViaBreak(int number) {
String result = switch (number) {
case 1, 2:
break "one or two";
case 3:
break "three";
case 4, 5, 6:
break "four or five or six";
default:
break "unknown";
};
return result;
}In Java 13, the above Java 12 value break is discarded and the yield keyword is used to return the value.
private static String getNumberViaYield(int number) {
return switch (number) {
case 1, 2:
yield "one or two";
case 3:
yield "three";
case 4, 5, 6:
yield "four or five or six";
default:
yield "unknown";
};
}Or something like that
private static String getNumberViaYield2(int number) {
return switch (number) {
case 1, 2:
yield "one or two";
case 3:
yield "three";
case 4, 5, 6:
int i = 0;
i++;
yield "four or five or six : " + i;
default:
yield "unknown";
};
}Java 13 still supports rule tags or arrows or case L
private static String getNumberViaCaseL(int number) {
return switch (number) {
case 1, 2 -> "one or two";
case 3 -> "three";
case 4, 5, 6 -> "four or five or six";
default -> "unknown";
};
}Or, like this, mix the arrow syntax with yield.
private static String getNumberViaCaseL2(int number) {
return switch (number) {
case 1, 2 -> "one or two";
case 3 -> "three";
case 4, 5, 6 -> {
int i = 0;
i++;
yield "four or five or six :" + 1;
}
default -> "unknown";
};
} Java 14
The switch expression becomes Java 14 – JEP 361 Standard features of.
be careful
For a complete example, read this Java 13 Switch Expressions.
JEP-355 text block (Preview)
The JEP finally introduces multi line string text, text block.
PS this is the preview language function in Java 13
Before Java 13
String html ="<html>\n" +
" <body>\n" +
" <p>Hello, World</p>\n" +
" </body>\n" +
"</html>\n";
String json ="{\n" +
" \"name\":\"mkyong\",\n" +
" \"age\":38\n" +
"}\n";Now Java 13
String html = """
<html>
<body>
<p>Hello, World</p>
</body>
</html>
""";
String json = """
{
"name":"mkyong",
"age":38
}
"""; Further reading
More multiline strings, examples of text blocks
be careful
This text block is in Java 14 With second Preview – JEP 368 , two new escape sequences were added:
- \< end of line > prohibit line termination.
- \s is translated into a space.
To enable the Java 13 preview feature:
javac --enable-preview --release 13 Example.java java --enable-preview Example
Download source code
$ git clone https://github.com/mkyong/core-java
$ cd java-13
reference
- OpenJDK 13 project
- Oracle – Java 13 coming!
- cl4cds
- Java version history
- Java 13 switch expression
- Java 13 data sharing with application classes
- Java 13 text block
- What are the new features of Java security?
- Java multiline string, text block example
Translated from: https://mkyong.com/java/what-is-new-in-java-13/