Part 1
Interview questions on Java 8 Lambda Expression for experienced covered in this post:
What are the features introduced in Java 8?
-
Following are the features introduced in Java 8.
1.
Lambda Expression.
2.
Functional Interface.
3.
Default methods in Interface.
4.
Static methods in Interface.
5.
Predicate functional interface.
6.
Function functional interface.
7.
Consumer functional interface.
8.
Method reference and constructor reference (::).
9.
Stream API.
10.
Date and Time (JODA API).
What is Lambda Expression?
-
Lambda expression is an anonymous function without having
return type, modifier and name.
-
To enable functional programming in Java we have to use a
lambda expression.
-
We can pass the procedure and function directly.
-
|
Normal Method. |
Lambda Expression. |
|
public
void
m1() {
System.out.println("Hello");
} |
System.out.println("Hello");
}
Lambda Expression will be like,
System.out.println("Hello");
}
|
|
public
void
m1(int a, int b) {
System.out.println(a+b);
} |
System.out.println("Hello");
}
Lambda Expression will be like,
System.out.println(a+b);
}
|
|
public
int
m1(String s) {
return s.length();
} |
return s.length();
}
Lambda Expression will be like,
return s.length();
}
|
-
If your lambda expression has only one line of code then it is allowed to
skp the curly braces {}.
1.
-
If your lambda expression has only one parameter then it is
allowed to skip parenthesis as well.
1.
-
If lambda expression return something then return keyword is
also optional.
1.
E.g. please refer above example.
-
Lambda expression can have body inside curly braces if there
are multiple statements.
1.
Statement 1;
Statement 2;
Statement 3;
};
 
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How will you identify lambda expression?
-
We can identify the the lambda expression with following
points.
1.
2.
If we are passing parameters without parenthesis if there is
only one parameter.
3.
If we are returning something without a return statement.
Please identify valid lambda expression?
-
() -> System.out.println("Hello");
-
(s) -> System.out.println("Java");
-
(a,10) -> {System.out.println(a);
System.out.println(10);}
-
(a,b) -> System.out.println(a+b);
-
s -> {System.out.println(s);}
-
(int a, int b) -> {System.out.println(a+b);}
-
s -> s.length();
-
(s) -> {s.length();}
|
Expression |
Valid / Invalid |
|
() -> System.out.println("Hello"); |
Valid |
|
(s) -> System.out.println("Java"); |
Valid |
|
(a,10) -> {System.out.println(a); System.out.println(10);} |
Valid |
|
(a,b) -> System.out.println(a+b); |
Valid |
|
s -> {System.out.println(s);} |
Valid |
|
(int a, int b) -> {System.out.println(a+b);} |
Valid |
|
s -> s.length(); |
Valid |
|
(s) -> {s.length();} |
Valid |
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