This is a draft cheat sheet. It is a work in progress and is not finished yet.
Lambda
Optional type declaration |
The compiler can infer the type |
Optional parenthesis around parameter |
For single parameter, no need for parens. Required for multiple parameters |
Optional curly braces |
If it contains a single statement |
Optional return keyword |
Compiler automatically returns the value. |
Facilitates functional programming.
Method references
Pass a method as a function parameter |
public class Java8Tester {
public static void main(String args[]){
List names = new ArrayList();
names.add("George");
names.add("Nowakowski");
names.forEach(System.out::println);
}
}
Optional Class
Optional.ofNullable() |
Returns a non-empty Optional if a value present in the given object. Otherwise returns an empty Optiona |
Optional.empty() |
empty Optional object |
Optional.isPresent() |
Returns true if the given Optional object is non-empty |
Optiona.ifPresent() |
Performs the given action if the Optional object is non-empty |
Optional.orElse() |
Returns the value if present. Otherwise returns the given default value |
Optional is a container object which is used to represent a value is present or absent.
Advantages:
1. Null checks are not required.
2. No more NPE at run-time
3. Encourages clean and neat APIs
4. No more Boiler plate code
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Streams
Sequence of elements |
A stream provides a set of elements of specific type in a sequential manner. |
Source |
Collections, Arrays, or I/O resources |
Aggregate operations |
filter, map, limit, reduce, find, match |
Pipelining |
Most stream operations return a stream, so their result can be pipelined. |
Automatic iterations |
Stream operations do the iterations internally |
stream() |
Returns a sequential stream considereing collection as its source |
parallelStream() |
Returns a parallel stream |
map |
maps each element to its corresponding result |
filter |
used to elminiate elements based ona criteria. |
limit |
used to reduce the size of the stream |
sorted |
Collectors |
Used to combine the result of processing on the elements of a stream. Can return a list or a string |
Stream represents a sequence of objects from a source, which supports aggregate functions.
The concept of stream that lets the developer to process data declaratively, rather than having to write loops.
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Method References
Help to point to methods by their names. A method reference is described using :: symbol. A method reference can be used to point to the following types of methods:
- Static methods
- Instance methods
- Constructors using new operator (TreeSet::new)
Nashorn JavaScript
Usage:
ScriptEngine engine =
new ScriptEngineManager().getEngineByName("nashorn");
engine.eval("print('Hello World! ');");
Or, you can read it in using a FileReader() then call functions:
engine.eval(new FileReader("testFun.js")
Invocable invocable = (Invocable) engine;
Object result =
invocable.invokeFunction("fun1", "Peter Parker");
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