Java 8

Question 1

[JAVA 8] What are the new features released in Java 8?

Answer 1

Lambda Expressions - Stream API - Date and Time API - Functional Interface - Interface Default and Static Methods - Optional - Base64 Encoding/Decoding - Nashorn JavaScript Engine - Collections API Enhancements - Concurrency Enhancements - Fork/Join Enhancements - Spliterator - Internal Iteration - Type and Repeatable Annotations - Method Parameter Reflection - JVM Parameter Changes

Question 2

[JAVA 8] What are the main benefits of the new features introduced in Java 8?

Answer 2

Functional programming via Lambda and Streams - high volume data processing - parameter names via Reflection - reusable Collection APIs - smart null handling with Optional - JVM control with new parameters - enhanced encryption with Base64 - faster execution with Nashorn

Question 3

[JAVA 8] Why did Oracle release Java 8?

Answer 3

The main theme of Java 8 is functional programming support. Growing database sizes and multi-core CPUs required Java to efficiently handle large-scale systems. Lambda and Streams enable Big Data interaction and cloud computing where code is passed as data across servers

Question 4

[JAVA 8] MEMORY BOOSTER: Java 8 key themes

Answer 4

Java 8 = Functional Programming. Top 5 features to know: Lambda (pass code as data) + Streams (data pipeline) + Optional (null safety) + Default Methods (backward compatibility) + new Date/Time API (thread-safe immutable dates)

Question 5

[JAVA 8] What is a Lambda expression in Java 8?

Answer 5

A Lambda expression is an anonymous function with no access modifier - no name and no return type declaration. It accepts parameters and returns a result. It can be passed as a parameter to a method treating code as data

Question 6

[JAVA 8] What are the three main parts of a Lambda expression?

Answer 6

1) Parameter list (zero or more parameters). 2) Arrow operator -> separating parameters from body. 3) Body containing the code to execute. Example: e -> System.out.println(e) has parameter=e and arrow=-> and body=println

Question 7

[JAVA 8] What is the data type of a Lambda expression?

Answer 7

The data type of a Lambda expression is a Functional Interface. In most cases this is java.lang.Runnable. The lambda provides the implementation of the single abstract method of the functional interface

Question 8

[JAVA 8] What are the advantages of a Lambda expression?

Answer 8

A lambda can be passed as an object to a method reducing overhead of anonymous classes. It enables passing a method as a parameter to another method. It makes code more concise and readable

Question 9

[JAVA 8] What is the target type of a Lambda expression?

Answer 9

The target type is the Functional Interface type to which the lambda can be converted. The lambda must match the parameter types and return type of the single abstract method of that interface

Question 10

[JAVA 8] What is the type of a Lambda expression in Java 8?

Answer 10

A lambda does not have a type of its own. Its type depends on the context it is used in. Generally a lambda is an instance of a Functional Interface

Question 11

[JAVA 8] MEMORY BOOSTER: Lambda expressions

Answer 11

Lambda = anonymous function = (params) -> body. No name + no modifier + no return type. Type = Functional Interface. Pass code as data. Short form of anonymous inner class for single-method interfaces

Question 12

[JAVA 8] What is a Functional interface in Java 8?

Answer 12

A Functional interface has exactly one abstract method. It can have default and static methods with implementation. Popular examples are Runnable and Callable. It serves as the data type for Lambda expressions

Question 13

[JAVA 8] What is a Single Abstract Method (SAM) interface?

Answer 13

SAM interface is another name for Functional Interface. It has exactly one abstract method. The term SAM highlights that there is only one method that must be implemented

Question 14

[JAVA 8] How can we define a Functional interface in Java 8?

Answer 14

Create an interface with exactly one abstract method. Optionally annotate it with @FunctionalInterface which makes the compiler enforce the one-abstract-method rule. Overriding Object class methods does not count as an abstract method

Question 15

[JAVA 8] Is @FunctionalInterface annotation mandatory?

Answer 15

No - it is not mandatory. But using it is recommended because the compiler will then give an error if you accidentally add a second abstract method to the interface

Question 16

[JAVA 8] Why do we need Functional interfaces in Java?

Answer 16

Functional interfaces are used in Lambda expressions - Method references and Constructor references. They serve as the data type for lambdas enabling functional programming style where code can be passed as data

Question 17

[JAVA 8] What are Predicate - Supplier and Consumer in Java 8?

Answer 17

Predicate = takes one argument + returns boolean result. Supplier = takes no argument + returns a result. Consumer = takes one argument + returns no result. All three are built-in functional interfaces in java.util.function

Question 18

[JAVA 8] MEMORY BOOSTER: Functional Interface

Answer 18

Functional Interface = exactly ONE abstract method = SAM. @FunctionalInterface enforces this at compile time. Lambda provides the implementation. Predicate (in+boolean out) - Supplier (nothing in+out) - Consumer (in+nothing out)

Question 19

[JAVA 8] What are the main differences between Collection and Stream API in Java 8?

Answer 19

Collection = stores data + finite elements + eager construction + multiple iterations. Stream = computes data + can be infinite + lazy construction + single consumption only. Collection is from Java 1.2. Stream is from Java 8

Question 20

[JAVA 8] What are the main uses of Stream API in Java 8?

Answer 20

Declarative data processing - multi-core utilization without multi-threading code - pipeline of sequential or parallel operations - group by and order by support - functional programming style - parallel data processing

Question 21

[JAVA 8] What are the differences between Intermediate and Terminal Operations in Streams?

Answer 21

Intermediate: lazy + output is another Stream + can be chained + multiple per statement. Terminal: eager + output is not a Stream + cannot be chained + only one per statement. Intermediate operations only execute when a Terminal operation is reached

Question 22

[JAVA 8] Can we consume a Stream more than once?

Answer 22

No - a Stream can only be consumed or iterated once. After a terminal operation is called the Stream is exhausted. To process the data again a new Stream must be created

Question 23

[JAVA 8] MEMORY BOOSTER: Stream API

Answer 23

Stream = pipeline + lazy + single use. Collection = container + eager + reusable. Intermediate ops = filter/map/sorted (lazy - chainable). Terminal ops = collect/forEach/count (eager - one only). Think of Stream as an assembly line that runs only when the final step is called

Question 24

[JAVA 8] What is a Spliterator in Java 8?

Answer 24

Spliterator is a special Iterator for traversing and partitioning elements of a source (Collection - IO channel or generator). It can traverse elements individually or in bulk and supports parallel as well as sequential iteration

Question 25

[JAVA 8] What are the differences between Iterator and Spliterator?

Answer 25

Spliterator works with Streams. Iterator works only with Collections. Spliterator uses internal iteration. Iterator uses external iteration. Spliterator supports parallel and sequential traversal and bulk operations. Iterator only supports sequential one-by-one traversal

Question 26

[JAVA 8] MEMORY BOOSTER: Spliterator

Answer 26

Spliterator = split + iterate. Designed for Streams and parallel processing. Can split source into parts for parallel processing. More powerful than Iterator: supports bulk - parallel and internal iteration

Question 27

[JAVA 8] What is Internal Iteration in Java 8?

Answer 27

In Internal Iteration the Iterator controls the iteration not the collection. The client passes an operation to the Iterator and the Iterator applies it to all elements. It is easier to implement and supports parallel processing

Question 28

[JAVA 8] What are the main differences between Internal and External Iterator?

Answer 28

Internal: Iterator controls iteration + declarative style + supports bulk and parallel + more readable. External: Collection controls iteration + imperative style + sequential only + one element at a time

Question 29

[JAVA 8] What is the main disadvantage of Internal Iteration?

Answer 29

The developer has no control over the iteration process since the Java API handles it. You cannot pause - skip or control the order of iteration like you can with an External Iterator

Question 30

[JAVA 8] MEMORY BOOSTER: Internal vs External Iteration

Answer 30

External = you control the loop (for loop - Iterator). Internal = API controls the loop (forEach - Streams). Internal is declarative: tell WHAT to do not HOW. External is imperative: tell HOW step by step. Streams use internal iteration

Question 31

[JAVA 8] What is a Default Method in a Java 8 Interface?

Answer 31

A Default method has a concrete implementation inside an interface marked with the default keyword. Any class implementing the interface inherits this default behavior without needing to override it

Question 32

[JAVA 8] Why do we need Default methods in Java 8 Interfaces?

Answer 32

Default methods provide backward compatibility. When a new method is added to an existing interface all implementing classes would break. A default implementation prevents this by providing fallback behavior for classes that do not override the method

Question 33

[JAVA 8] What is the purpose of a Static method in a Java 8 Interface?

Answer 33

Static interface methods are utility or helper methods. They avoid the need for a separate Utils class - keep behavior encapsulated in one place and are called using the interface name not an instance

Question 34

[JAVA 8] Can we create a class implementing two interfaces with default methods of the same name?

Answer 34

No - this causes a compile-time error for duplicate default methods. The class must override the method and explicitly specify which interface implementation to use via InterfaceName.super.methodName()

Question 35

[JAVA 8] How does Java 8 solve the Diamond Problem?

Answer 35

When a class inherits the same default method from two interfaces it must override the method and call the desired implementation explicitly using InterfaceName.super.methodName(). This resolves the compiler ambiguity

Question 36

[JAVA 8] What are the differences between an interface with default method and an abstract class?

Answer 36

Interface: no instance variables + no constructor + only default/static concrete methods + can be used for lambda. Abstract class: can have instance variables + constructors + any concrete methods + cannot be used for lambda

Question 37

[JAVA 8] If a class extends a base class and implements an interface with the same default method which wins?

Answer 37

The base class definition wins. JVM always picks the class implementation over the interface default method

Question 38

[JAVA 8] MEMORY BOOSTER: Default and Static interface methods

Answer 38

Default = instance method with body in interface + keyword default + inheritable + overridable. Static = utility method in interface + call via InterfaceName.method(). Both added in Java 8. Class always beats interface default. Interface A beats Interface B if A is more specific

Question 39

[JAVA 8] What is Optional in Java 8?

Answer 39

Optional is a container object that may hold a null or non-null value. Use isPresent() to check if a value exists and get() to retrieve it. It is used to avoid NullPointerException and make null handling explicit

Question 40

[JAVA 8] What are the uses of Optional in Java 8?

Answer 40

Avoid NullPointerException - perform null checks at compile time instead of runtime - reduce unnecessary null checks in code - provide default values for null cases using orElse() or orElseGet()

Question 41

[JAVA 8] Which method in Optional provides a fallback for null values?

Answer 41

orElseGet() provides a fallback mechanism. If the Optional contains null - orElseGet() invokes the provided Supplier to return a default value. orElse() returns a direct default value

Question 42

[JAVA 8] MEMORY BOOSTER: Optional

Answer 42

Optional = null-safe wrapper. isPresent() = has value? get() = retrieve value. orElse(default) = value or fallback. orElseGet(supplier) = value or computed fallback. ifPresent(consumer) = do something only if value exists. Replaces explicit null checks

Question 43

[JAVA 8] What are the core ideas behind the Java 8 Date/Time API?

Answer 43

Three core ideas: Immutable value classes (thread-safe) + Domain-driven design (classes model real date/time concepts) + Separation of chronologies (supports non-ISO calendar systems like Japanese or Thai)

Question 44

[JAVA 8] What are the advantages of the Java 8 Date/Time API over the old Date API?

Answer 44

Thread-safe immutable classes - better API design (months 1-12 not 0-11) - no need for third-party libraries like Joda Time - clearer domain model - better performance

Question 45

[JAVA 8] What are the main differences between legacy Date API and Java 8 Date/Time API?

Answer 45

Old: not thread-safe + mutable + poor performance + months 0-11. New: thread-safe + immutable + better performance + months 1-12 + clear readable API

Question 46

[JAVA 8] How can we get duration between two dates in Java 8?

Answer 46

Use the Duration class: Duration.between(date1 - date2) returns the time period between two dates in days - hours - minutes or seconds

Question 47

[JAVA 8] How can we get the current time using the Java 8 Date/Time API?

Answer 47

Use the Clock class: Clock.systemDefaultZone().millis() for milliseconds or Clock.systemDefaultZone().instant() for a human-readable format. Replaces the old System.currentTimeMillis()

Question 48

[JAVA 8] MEMORY BOOSTER: Java 8 Date/Time API

Answer 48

Key classes: LocalDate (date only) - LocalTime (time only) - LocalDateTime (both) - ZonedDateTime (with timezone) - Duration (time between instants) - Clock (current time). All immutable + thread-safe. Months are 1-12

Question 49

[JAVA 8] What new Array methods were introduced in Java 8 for multi-core machines?

Answer 49

Java 8 added parallel prefix methods to the Arrays class: Arrays.parallelSort() - Arrays.parallelSetAll() and Arrays.parallelPrefix(). These methods leverage multiple CPU cores for fast array processing

Question 50

[JAVA 8] What are the popular annotations introduced in Java 8?

Answer 50

@FunctionalInterface marks an interface as a Functional Interface and enforces single abstract method at compile time. @Repeatable marks an annotation as one that can be applied multiple times to the same element

Question 51

[JAVA 8] What is StringJoiner in Java 8?

Answer 51

StringJoiner is a new class in Java 8 for building strings with a delimiter and optional prefix/suffix. new StringJoiner(":" - "[" - "]").add("One").add("Two").toString() produces [One:Two]

Question 52

[JAVA 8] What are the new JVM arguments introduced in Java 8?

Answer 52

PermGen space was removed and replaced with MetaSpace. JVM options -XX:PermSize and -XX:MaxPermSize are replaced by -XX:MetaSpaceSize and -XX:MaxMetaspaceSize. MetaSpace grows dynamically by default

Question 53

[JAVA 8] What is jdeps in Java 8?

Answer 53

jdeps is a new command-line tool in Java 8 for analyzing class-level and package-level dependencies. Pass a class name or jar file to get a full list of its dependencies

Question 54

[JAVA 8] MEMORY BOOSTER: Java 8 JVM changes

Answer 54

PermGen OUT - MetaSpace IN. PermGen had fixed size and caused OutOfMemoryError. MetaSpace uses native memory and grows dynamically. New flags: -XX:MetaSpaceSize and -XX:MaxMetaspaceSize. jdeps tool for dependency analysis