Following are the top 10 improvements impressed me over previous version of JDK. In a nutshell, I summarized below for quick look up.

•  Underscores in Numeric Literals

   long ssn = 999_99_9999L

• Strings in Switch Statements

String month = "Feb";
  switch(month) {
     case "January"  : <do some thing> ;break;
     case "February" : <do some thing> ;break;
     default : <do some thing> ;break;
  }

• Automatic Resource Management

  Inout/Ouput streams need not be closed explicitly. JVM will take care of closing them when needed.

  Extended to classes which implements java.lang.AutoCloseable

  Syntax:

try( InputStream in = new FileInputStream(new File("text.txt"))){
     // your code
}

• Multi-Catch Statements - group relevant types

try{
   ...
  } catch(InstantiationException | NoSuchMethodException | InvocationTargetException e){
     log(e);
  }     

• New Enhanced IO package(NIO2)

Some of the new classes: java.nio.file.Paths, java.nio.file.Files, java.nio.file.FileSystem

features added to watch a directory for any changes, create a symbolic links, file copy is made easy.

• Enhanced Concurrancy API

• Bug Fixes on JAXP, JAX-WS, JAXB

• JDBC 4.1

Connection, ResultSet and Statement = > now we don't need to close them manually as they implement AutoCloseable interface.

• Fork and Join Framework

• Diamond operator works many ways.

  Foo<Bar> bar=new Foo<>();