Stream Api.pdf
- 2. CONTENT • Introduction • Lambda Expression • Functional Interfaces • Default methods • Predicates • Functions • Double colon operator • Stream API • Date and Time API • Project
- 3. Introduction • java 7 – July 28th 2011 • Java 8 - March 18th 2014 • Java 9 - September 22nd 2016 • Java 10 – 2018 • After Java 1.5version, Java 8 is the next major version. Before Java 8, sun people gave importance only for objects but in 1.8version oracle people gave the importance for functional aspects of programming to bring its benefits to Java.ie it doesn’t mean Java is functional oriented programming language
- 4. Lambda Expression • Lambda Expression is just an anonymous (nameless) function. That means the function which doesn’t have the name, return type and access modifiers. public void m1() { sop(“hello”); } () ->{ sop(“hello”); }
- 5. Functional Interfaces • If an interface contain only one abstract method, such type of interfaces are called functional interfaces and the method is called functional method or single abstract method (SAM) • Ex-> • 1) Runnable -> It contains only run() method • 2) Comparable ->It contains only compareTo() method • 3) ActionListener -> It contains only actionPerformed() • 4) Callable -> It contains only call() method interface Interf { public abstract void m1(); default void m2() { System.out.println (“hello”); } } @Functional Interface Interface Interf { public void m1(); }
- 6. Default methods • Until 1.7 version onwards inside interface we can take only public abstract methods and public static final variables • But from 1.8 version onwards in addition to these, we can declare default concrete methods also inside interface, which are also known as defender methods. default void m1() { System.out.println (“Default Method”); } • Interface default methods are by-default available to all implementation classes. Based on requirement implementation class can use these default methods directly or can override
- 7. Predicates • A predicate is a function with a single argument and returns boolean value. • To implement predicate functions in Java, Oracle people introduced Predicate interface in 1.8 version (i.e.,Predicate) • Predicate interface present in Java.util.function package. • public boolean test(Integer I) { if (I >10) { return true; } else { return false; } } With predicate predicate p = I ->(I >10); System.out.println (p.test(100)); true System.out.println (p.test(7)); false
- 8. Functions • Functions are exactly same as predicates except that functions can return any type of result but function should (can) return only one value and that value can be any type as per our requirement • To implement functions oracle people introduced Function interface in 1.8version. • interface function(T,R) { • public R apply(T t); • }
- 9. Double colon operator • Functional Interface method can be mapped to our specified method by using :: (double colon) operator. This is called method reference. • Our specified method can be either static method or instance method Syntax: if our specified method is static method Classname::methodName if the method is instance method Objref::methodName
- 10. Stream API • To process objects of the collection, in 1.8 version Streams concept introduced. • java.util streams meant for processing objects from the collection. I and Java.io streams meant for processing binary and character data with respect to file. • We can create a stream object to the collection by using stream() method of Collection interface. stream() method is a default method added to the Collection in 1.8 version. • default Stream stream() • Stream s = c.stream(); • Stream is an interface present in java.util.stream. Once we got the stream, by using that we can process objects of that collection. We can process the objects in the following 2 phases • Configuration • Mapping
- 11. Date and Time API • Joda-Time API • Until Java 1.7version the classes present in Java.util package to handle Date and Time (like Date, Calendar, TimeZoneetc) are not up to the mark with respect to convenience and performance. • To overcome this problem in the 1.8version oracle people introduced Joda-Time API. This API developed by joda.org and available in Java in the form of Java.time package.
- 13. THANK YOU