Why

Java 8 > Java 6/7

Java 8/JDK8 provides:

• Lambdas!
• Local type inference
• Default methods
• Streams API
• Date and Time API

Problem

Solution

Lambdas

The hardest part

Java 6

button.setOnClickListener(new View.OnClickListener() {
    @Override                                         
    public void onClick(View view) {                  
        view.setEnabled(false);                       
    }                                                 
});                                                   

Sollution

Retrolambda

How does it work?

1. Take Java 8 code
2. Compile it with javac from JDK8
3. Process bytecode
4. ?????????????
5. PROFIT

Retrolamda support

• Lambdas
• Serializable lambdas
• Method references
• Try-with-resources
• Default Methods
• Static method in interfaces

Easy to use with gradle

buildscript {
  repositories {
     mavenCentral()
  }

  dependencies {
     classpath 'me.tatarka:gradle-retrolambda:3.2.2'
  }
}

// Required because retrolambda is on maven central
repositories {
  mavenCentral()
}

apply plugin: 'com.android.application' //or apply plugin: 'java'
apply plugin: 'me.tatarka.retrolambda'

One more thing

//anonymous class holds outer reference                   
button.setOnClickListener(new View.OnClickListener() {    
    @Override                                             
    public void onClick(View view) {                      
        view.setEnabled(false);                           
    }                                                     
});                                                       
                                                          
                                                          
//do not hold reference to outer class                    
button.setOnClickListener(view -> view.setEnabled(false));

Avoid memory leaks

Streams API

Streamsupport

backport of streams

Java 8/Streams

Java 6/Streamsupport

List<String> myList =                         
  Arrays.asList("a1", "a2", "b1", "c2", "c1");
                                              
myList.stream()                               
        .filter(s -> s.startsWith("c"))       
        .map(String::toUpperCase)             
        .sorted()                             
        .forEach(System.out::println);        

List<String> myList =                         
  Arrays.asList("a1", "a2", "b1", "c2", "c1");
                                              
StreamSupport.stream(myList)                  
        .filter(s -> s.startsWith("c"))       
        .map(String::toUpperCase)             
        .sorted()                             
        .forEach(System.out::println);        

Date and Time

ThreeTen

Backport of JSR-310 API

    // The current date and time
    LocalDateTime dateTime = LocalDateTime.now();
    // from values
    LocalDate d1 = LocalDate.of(2015, Month.SEPTEMBER, 17);

    // construct time object based on hours and minutes
    LocalTime t1 = LocalTime.of(17, 18);
    // create time object based on a String
    LocalTime t2 = LocalTime.parse("10:15:30");

    // Get the time or date from LocalDateTime
    LocalDate date = dateTime.toLocalDate();
    Month month = dateTime.getMonth();
    int day = dateTime.getDayOfMonth();
    int minute = dateTime.getMinute();
    
    
    // Perform operations on these objects will always return a new object
    // as these objects are immutable
    
    LocalDateTime updatedDate = dateTime.withDayOfMonth(13).withYear(2015);
    LocalDateTime plusYears = updatedDate.plusDays(25).plusYears(2);
    
    // the API also allow to use Adjusters for the API,
    // for example the following will set the day to the last day in the monthd
    LocalDateTime newDate = dateTime.with(TemporalAdjusters.lastDayOfMonth());
    
    // You can also truncate certain time units, e.g., remove the seconds from a time 
    // object
    LocalTime truncatedSeconds = t2.truncatedTo(ChronoUnit.SECONDS);