Java 7 Features You (Probably) Didn't Hear About
Underscores in Numeric Literals
•Valid:
int mask = 0b1010_1010_1010;long big = 9_223_783_036_967_937L;long creditCardNumber = 1234_5678_9012_3456L;long socialSecurityNumber = 999_99_9999L;float pi = 3.14_15F;long hexBytes = 0xFF_EC_DE_5E;long hexWords = 0xCAFE_BFFE;
•Invalid:
float pi1 = 3_.1415F;float pi2 = 3._1415F;
long ssn = 999_99_9999_L;int x1 = _52;int x1 = 52_;
int x2 = 0_x52;int x2 = 0x_52;
Strings in Switch Statements
int monthNameToDays(String s, int year) {switch(s) {
case "April": case "June":
case "September": case "November":
return 30;
case "January": case "March":
case "May": case "July":
case "August": case "December":
return 31;
case "February”:
...
default:
...
}
NOTE:-
Did you know it produces generally more efficient byte codes than an if-then-else statement? Case Sensitive!
Diamond Operator works many ways…
With diamond (<>) compiler infers type…List<String>strList = new ArrayList<>();
OR
List<Map<String, List<String>>strList =
new ArrayList<>();
OR
Foo<Bar> foo = new Foo<>();
foo.mergeFoo(new Foo<>());
Multi-Catch
try {...
} catch (ClassCastException e) {
doSomethingClever(e);
throw e;
} catch(InstantiationException |
NoSuchMethodException |
InvocationTargetException e) {
// Useful if you do generic actions
log(e);
throw e;
}
More Precise Rethrow
public void foo(String bar)throws FirstException, SecondException{
try {
// Code that may throw both
// FirstException and SecondException
}
catch (Exception e) {
throw e;
}
}
NOTE:-
•Prior to Java 7, this code would not compile, the types in throws would have to match the types in catch –foo would have to “throws Exception”
•Java 7 adds support for this as long as try block calls all the exceptions in the throws clause, that the variable in the catch clause is the variable that is rethrown and the exceptions are not caught by another catch block.
Varargs Warnings –Erasure
class Test {public static void main(String... args) {
List<List<String>> monthsInTwoLanguages =
Arrays.asList(Arrays.asList("January",
"February"),
Arrays.asList("Gennaio",
"Febbraio" ));
}
}
Test.java:7: warning:
[unchecked] unchecked generic array creation
for varargs parameter of type List<String>[]
Arrays.asList(Arrays.asList("January",
^
1 warning
@SuppressWarnings(value = “unchecked”) // at call
@SafeVarargs // at declaration
Java NIO.2 –File Navigation
Two key navigation Helper Types:•Class java.nio.file.Paths
•Exclusively static methods to return a Path by converting a string or Uniform Resource Identifier (URI)
•Interface java.nio.file.Path
•Used for objects that represent the location of a file in a file system, typically system dependent.
Typical use case:
Use Paths to get a Path. Use Files to do stuff.
Java NIO.2 Features –Files Helper Class
•Class java.nio.file.Files•Exclusively static methods to operate on files, directories and other types of files
•Files helper class is feature rich:
•Copy
•Create Directories
•Create Files
•Create Links
•Use of system “temp” directory
•Delete
•Attributes –Modified/Owner/Permissions/Size, etc.
•Read/Write
Files.move(src, dst, StandardCopyOption.ATOMIC_MOVE);
Files.copy(src, dst,
StandardCopyOption.COPY_ATTRIBUTES,
StandardCopyOption.REPLACE_EXISTING);
Java NIO.2 Directories
•DirectoryStream iterate over entries
–
Scales to large directories
–
Uses less resources
–
Smooth out response time for remote file systems
–
Implements Iterableand Closeablefor productivity
•Filtering support
–
Build-in support for glob, regex and custom filters
Path srcPath = Paths.get(“/home/fred/src”);
try (DirectoryStream<Path> dir =
srcPath.newDirectoryStream(“*.java”)) {
for (Path file : dir)
System.out.println(file.getName());
}
Standardize Nimbus Look and Feel
•Better than Metal for cross platform look-and-feel•Introduced in Java SE 6u10, now part of Swing
•Not the default L&F
•Scalable Java 2D impl
Mixing of AWT and Swing –Works*
•As of 6u12 and 7u1, some caveats for scroll barsJDBC 4.1
•Try-with-resources statement to automatically close resources of typeConnection,ResultSet, andStatementtry (Statement stmt = con.createStatement()) { // ... }
•RowSet 1.1 introduces RowSetFactoryand RowSetProvider
//Factory options (impl) set on cmd line or metainf
myRowSetFactory = RowSetProvider.newFactory();
jdbcRs = myRowSetFactory.createJdbcRowSet();
jdbcRs.setUrl("jdbc:myDriver:myAttribute"); //etc
jdbcRs.setCommand("select COF_NAME, SUP_ID, PRICE, SALES, TOTAL from COFFEES");
jdbcRs.execute();
Draggable Applet Decoration
•Applet decoration settings apply equally to in browser and out of browser launches –borderless, etc.JavaDoc Improvements in Java 7
•Section 508 accessibility guidelines•Captions, headings, etc.
•Previously, JavaDoc wrote to an OutputStream on the fly meaning it built the document sequentially, imposing limitations
•Now uses internal “HTMLTree” classes
•Generates compliant HTML
•Allows for more advancements in the future
•Removes limitation of only being able to execute only once in any VM
•Was fine when used as a command line tool
•Continuous build, etc, made it necessary to address this!
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