what is lambda expression in java

1A lambda expression is a short block 
2of code which takes in parameters
3and returns a value. Lambda expressions
4are similar to methods, but they do
5not need a name and they can be
6implemented right in the body of a method.
7
8parameter -> expression
9
10To use more than one parameter, wrap them in parentheses:
11
12(parameter1, parameter2) -> expression
13
14Example
15Use a lamba expression in the ArrayList's 
16forEach() method to print every item in the list:
17
18import java.util.ArrayList;
19
20public class Main {
21  public static void main(String[] args) {
22    ArrayList<Integer> numbers = new ArrayList<Integer>();
23    numbers.add(5);
24    numbers.add(9);
25    numbers.add(8);
26    numbers.add(1);
27    numbers.forEach( (n) -> { System.out.println(n); } );
28  }
29}

1StateOwner stateOwner = new StateOwner();
2
3stateOwner.addStateListener(
4    (oldState, newState) -> System.out.println("State changed")
5);
6

1public class TestLambda {
2
3   public static void main(String args[]) {
4      List<String> lowerCaseStringsList = Arrays.asList("a","b","c");
5     // the :: notation is the lambda expression
6     // it's the same as the anonymous function s -> s.toUpperCase()
7      List<String> upperCaseStringsList = lowerCaseStringsList.stream().
8        map(String::toUpperCase).
9        collect(Collectors.toList());
10   }   
11}

1Lambda Expression