Lambda Expression is newly added feature in Java 8, which is like a Javascript Closure or Scala, where function or reference of a function, together with a referencing environment a table storing a reference to each of the non-local variables of that function. So, we can say Lambda expression is similar to Closure or Scala, but not 100%.
like -
---------------------------------------------
var add = (function () {
var counter = 0;
return function () {return counter += 1;}
})();
add();
add();
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So we can say Lambda Expressions, a new language feature, That enable you to treat functionality as a method argument, or code as data. Lambda expressions let you express instances of single-method interfaces (referred to as functional interfaces) more compactly.
Lambda expression is short form of writing method, and can be used in multiple ways. syntax is given below-
Lambda Expression syntax
(argument...)
-> {statement}Here method name, return type, and access modifier is not require to mention.above is replica of below in old javaAccessmodifier ReturnType methodname(argument){ //method statement }
Lambda can be written in some more ways-
() -> 10
// no parameter and returns 10
x -> x * x
// a number parameter parameter and returns the squared of number
(x, y) -> x – y
// two numbers parameter and returns their difference
(int x, int y) -> x + y
//two integers number and returns their sum
(String s) -> System.out.print(s)
//string parameter and prints output to console
As you now aware of some basic syntax of Lambda expression so see some expmple below-
-------------------------------------------String[] array= {"ABC", "BCD", "DEF", "GHI"};
List<String> list= Arrays.asList(array);
new way coding style-
list.forEach((item)-> System.out.println(item));
old way coding style-
for (String item: list) {
System.out.println(item);
}
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Method reference is also java 8 feature which you can plug with Lambda expression and get some more shorter way of code. It denote by :: (two colon) operator. method references; shortcuts that you can use anywhere you would use a lambda. There are four types of method referenc-
- Reference to a static method-
ContainingClass::staticMethodName - Reference to an instance method of a particular object -
ContainingObject::instanceMethodName - Reference to an instance method of an arbitrary object of a particular type -
ContainingType::methodName Reference to a constructor-ClassName::new
As Method Reference As Lambda Expression
String::valueOf (str) -> String.valueOf(str)x::toString () -> "test".toString() String::toString (s) -> s.toString() String::new () -> new String()---------------------------------------------------------------
//Iterate item by Method reference (::) two colon operator//by using reference to a static method
list.forEach(System.out::println);
//instance method of object call
String x = "test";
function(x::toString);
------------------------------------------------Anonymous classes also can be replaced with lambda expressions.
The same thing happens when implementing the Runnable interface
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// older style thread example
new Thread(new Runnable() {
@Override
public void run() {
System.out.println("Thread example");
}
}).start();
// Using lambda expression thread
new Thread(() -> System.out.println("Thread example")).start();
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Lambda with Stream
Java 8 added some Stream APIs. java.util.stream.Stream interface.
So, these Collection Stream method can be used by Lambda. like- map,
filter,limit, max, min, sort and so on.
---------------------------------------- //Old way of codingList<Integer> list = Arrays.asList(1,2,3,4,5,6,7);for(Integer n : list) { int x = n * n; //calculate the square of number System.out.println(x);}//New way of codingList<Integer> list = Arrays.asList(1,2,3,4,5,6,7);list.stream().map((x) -> x*x).forEach(System.out::println);Here we are getting the stream() and mapping all the stream element to x -> x*x then we are using method reference to print all the squared value.--------------------------------------------------
That's it about Lambda!!!!
