Evolution of Java, from Java 5 to 8
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Evolution Of Java From Java 5 to 8
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A recap of the evolution of Java starting with the JDK5 and finishing with the new api of date/time and lamdbas. The code is in github (https://github.com/nhpatt/evolution_of_java), showing how to do it in Java 5 and 8.
Transcript of Evolution of Java, from Java 5 to 8
Evolution Of
Java
From Java 5 to 8
State of the union
• Currently in Java 7
o Luce has some projects working with Java 7
(ipamms, aernova…), the rest of them are Java 6.
• Java 8 expected in spring 2014.
Java 5
• September 2004 (old!, almost 9 years)
o Annotations
o Generics
List values = new ArrayList();
values.add("value 1");
values.add(3);
String value=(String) values.get(0);
String value2=(String) values.get(1);
List<String> values = new ArrayList<String>();
values.add("value 1");
values.add(new Integer(3));
String value= values.get(0);
Integer value1= values.get(1);
OLDER JAVA JAVA 5
Compiled, but exception at runtime!! compilation error
Java 5
o Autoboxing/unboxing
List<Integer> values = new ArrayList<Integer>();
values.add(3);
int value=values.get(0);
JAVA 5
value=primitive;
BOXING
primitive=value
;
UNBOXINGAutomatic operation
With generics the type can’t be a
primitive, but is not a problem
Integer value;
int primitive;
o Enumerations: Special data type that enables for a variable to be a set of
predefined constants
public enum State{
INCOMPLETE("Incompl","YELLOW"),CORRECT("Correct","GREEN"), INCORRECT("Incorrect","RED");
private String name;
private String color;
private State(final String name, final String color) {
this.name = name;
this.color=color;
}
public String getName() {
return name;
}
public String getColor() {
return color;
}
public static List<State> getStateValues() {
return Arrays.asList(INCOMPLETE, CORRECT,INCORRECT);
}
}
private State state=State.CORRECT;
Assert.assertEquals("GREEN", state.getColor());
Java 5
String result = "";
for (int i = 0; i < values.size(); i++) {
result += values.get(i) + "-";
}
String result = "";
for (final String value : values) {
result += value + "-";
}
OLDER JAVA JAVA 5
o Foreach
o Static imports
double r = Math.cos(PI * theta);
OLDER JAVA JAVA 5
double r = Math.cos(Math.PI * theta);
sumTwo(2, 2)); //two numbers
sumThree(2, 2, 2)); //three numbers
public int sumTwo(final int a, final int b) {
return a + b;
}
public int sumThree(final int a, final int b,
final int c) {
return a + b + c;
}
sum(2, 2)); //two numbers
sum(2, 2, 2)); //three numbers
public int sum(final int... numbers) {
int total = 0;
for (final int number :
numbers) {
total += number;
}
return total;
}
OLDER JAVA JAVA 5
o Varargs
Java 5
Java 6
• December 2006
o No language changes
o Scripting support
o Improvements in Swing
o JDBC 4.0 support
o ...
Java 7
• July 2011 (ok, now we are talking)
o JVM support for dynamic languages
o Binary integer literals/underscores
o Varargs simplified
int million = 1_000_000
int telephone = 983_71_25_03
int num = 0b101
public String getColor (final String state) {
if (("correct".equals(state)) {
return "green";
} else if("incorrect".equals(state)) {
return "red";
} else if ("incomplete".equals(state)){
return "yellow";
} else {
return "white";
}
}
public String getColor(final String state) {
switch (state) {
case "correct":
return "green";
case "incorrect":
return "red";
case "incomplete":
return "yellow";
default:
return "white";
}
}
OLDER JAVA STRINGS IN SWITCH - JAVA 7
o Strings in switch
public void newFile() {
FileOutputStream fos = null;
DataOutputStream dos = null;
try {
fos = new
FileOutputStream("path.txt");
dos = new DataOutputStream(fos);
dos.writeBytes("prueba");
} catch (final IOException e) {
e.printStackTrace();
} finally { // close resources
try {
dos.close();
fos.close();
} catch (final IOException e) {
e.printStackTrace();
}
}
}
public boolean newFile() {
try (FileOutputStream fos = new
FileOutputStream("path.txt");
DataOutputStream dos = new DataOutputStream(fos);)
{
dos.writeBytes("prueba");
dos.writeBytes("\r\n");
} catch (final IOException e) {
e.printStackTrace();
}
}
OLDER JAVA
TRY WITH RESOURCES (ARM) - JAVA 7
o Automatic resource management in try-
catch
private Map<Integer, List<String>> createMapOfValues(final int... keys) {
final Map<Integer, List<String>> map = new HashMap<Integer,
List<String>>();
for (final int key : keys) {
map.put(key, getListOfValues());
}
return map;
}
private Map<Integer, List<String>> createMapOfValues(final int... keys) {
final Map<Integer, List<String>> map = new HashMap<>();
for (final int key : keys) {
map.put(key, getListOfValues());
}
return map;
}
OLDER JAVA
DIAMOND OPERATOR - JAVA 7
private ArrayList<String> getListOfValues() {
return new ArrayList<String>(Arrays.asList("value1",
"value2"));
}
private ArrayList<String> getListOfValues() {
return new ArrayList<>(Arrays.asList("value1",
"value2"));
}
o Diamond Operator
public double divide() {
double result = 0d;
try {
int a = Integer.parseInt(num1);
int b = Integer.parseInt(num2);
result = a / b;
} catch (NumberFormatException ex1) {
System.out.println("invalid number");
} catch (ArithmeticException ex2) {
System.out.println("zero");
} catch (Exception e) {
e.printStackTrace();
}
return result;
}
public double divide(){
double result = 0d;
try {
int a = Integer.parseInt(num1);
int b = Integer.parseInt(num2);
result = a / b;
} catch (NumberFormatException|ArithmeticException ex){
System.out.println("invalid number or zero");
} catch (Exception e) {
e.printStackTrace();
}
return result;
}
OLDER JAVA
MULTI CATCH - JAVA 7
o Catch multiple exceptions
Java 7
• New File I/O
Path path = Paths.get("C:\\Users/Pili/Documents/f.txt");
path.getFileName(); -> "f.txt"
path.getName(0); -> "Users"
path.getNameCount(); -> 4
path.subpath(0, 2); -> "Users/Pili"
path.getParent(); -> "C:\\Users/Pili/Documents"
path.getRoot(); -> "C:\\"
path.startsWith("C:\\Users"); -> true
for (final Path name : path) {
System.out.println(name);
}
java.io.File
o Solves problems
o New methods to
manipulate files
java.nio.file.Path
final File file = new File(path);
file.createNewFile();
final Path file= Paths.get(path);
Files.createFile(file);
new file new file
BufferedWriter bw = null;
try {
bw =new BufferedWriter(new FileWriter(file));
bw.write("Older Java: This is first line");
bw.newLine();
bw.write("Older Java: This is second line");
} catch (final IOException e) {
e.printStackTrace();
} finally {
try {
bw.close();
} catch (final IOException ex) {
System.out.println("Error");
}
}
try (BufferedWriter writer =
Files.newBufferedWriter(file,Charset.defaultCharset())
) {
writer.append("Java 7: This is first line");
writer.newLine();
writer.append("Java 7: This is second line");
} catch (final IOException exception) {
System.out.println("Error");
}
write file write file
BufferedReader br = null;
try {
br = new BufferedReader(new FileReader(file));
String content;
while ((content = br.readLine()) != null) {
System.out.println(content);
}
} catch (final IOException e) {
e.printStackTrace();
} finally {
try{
br.close();
} catch (final IOException ex) {
System.out.println("Error");
}
}
try (BufferedReader reader = Files.newBufferedReader
(file, Charset.defaultCharset())) {
String content= "";
while ((content = reader.readLine()) != null) {
System.out.println(content);
}
} catch (final IOException exception) {
System.out.println("Error");
}
read file readfile
file.delete(); Files.delete(file);
delete file delete file
Java 8
• Spring 2014?
o PermGen space disappears, new Metaspace
OutOfMemory errors disappear? -> not so fast
o New methods in Collections (almost all lambda-
related)
o Small changes everywhere (concurrency, generics,
String, File, Math)
Java 8
• Interfaces with static and default methods
o ¿WTF?
o Let’s look at Eclipse...
Java 8
public interface
CalculatorInterfacePreJava8 {
Integer add(Integer x, Integer y);
// WTF do u think you are doing?
// static Integer convert(Integer x);
}
public interface
CalculatorInterfaceJava8 {
default Integer add(Integer x, Integer
y) {
return x + y;
}
static Integer convert(Integer x) {
return x * MAGIC_CONSTANT;
}
}
OLDER JAVA JAVA 8
Java 8
• new Date and Time API (joda inspired)
o Current was based on currentTimeMillis, Date and
Calendar.
o New one is based on continuous time and human
time.
o Inmutable.
Java 8
//Date oldDate = new Date(1984, 7, 8);
oldDate = Calendar.getInstance();
oldDate.set(1984, 7, 8);
date =
LocalDate.of(1984, Month.AUGUST, 8);
dateTime = LocalDateTime.of(1984,
Month.AUGUST, 8, 13, 0);
OLDER JAVA JAVA 8
Java 8
oldDate.set(Calendar.DAY_OF_MONTH,
oldDate.get(Calendar.DAY_OF_MONT
H) - 2);
LocalDate sixOfAugust =
date.minusDays(2);
OLDER JAVA JAVA 8
Java 8
• Easier to add hours/days/… (plusDaysTest)
• Easier to set date at midnight/noon (atStartOfDayTest)
• Similar way to use instant time
• Easier to format and ISO dates supported right-out-the-
box
• Months/days start at 1!
Java 8
• How can I find the number of years between
two dates
• Get next wednesday
• Calculate flight time
Java 8
• Lambda expressions! (at last)
o Anonymous functions with special properties
Java 8
(int x, int y) -> { return x + y; }
Java 8
(x, y) -> { return x + y; }
Java 8
(x, y) -> x + y
Java 8
() -> x
Java 8
System.out.println(message)
Java 8
Implements a functional interface
Java 8
Classic Iteration
Java 8
for (final String text : strings) {
doSomething(text);
}
strings.forEach(this::doSometh
ing);
OLDER JAVA JAVA 8
Java 8
Classic Filtering (and no-reuse)
Java 8
List<String> longWords = new
ArrayList<String>();
for (final String text : strings) {
if (text.length() > 3) {
longWords.add(text);
}
}
List<String> longWords =
strings.stream().
filter(e -> e.length() > 3)
.collect(Collectors.<String>
toList());
OLDER JAVA JAVA 8
Java 8
Streams!
Java 8
Integer maxCool = 0;
User coolestUser = null;
for (User user : coolUsers) {
if (maxCool <=
user.getCoolnessFactor()) {
coolestUser = user;
}
}
User coolestUser = coolUsers.stream().
reduce(this::coolest).get();
OLDER JAVA JAVA 8
Java 8
Optional
Java 8
Infinite Streams (Lazy)
Java 8
Parallelizable Operations
Java 8
• More expressive language
• Generalization
• Composability
• Internal vs External iteration
• Laziness & parallelism
• Reusability
The Future?
• 2014 is right around the corner…
• Java 9, 2016?
o Modularization (project Jigsaw)
o Money and Currency API
o Hope it is not this.
References
• Examples in github
• JDK 8 early access & eclipse with Java 8 support (+plugin)
• Slides that inspired this talk
• Quick survey of Java 7 features
• Quick survey of Java 8 features
• New Date and Time API
• Good presentation of Java 8
• There is even a book (wait, Java 8 isn’t live yet!)
Evolution Of
Java
From Java 5 to 8
