Lambda Methods and Anonymous Classes Flashcards

Questions and Answers

What are anonymous classes?

It is an inner class without a name and for which only a single object is created. An anonymous class has the following properties: only one instance exists, it is typically declared within a method, and an instance is returned to the caller.

Why would we use anonymous classes?

An anonymous inner class can be useful for creating an instance of an object with certain 'extras' like overloading methods, without subclassing. They are particularly helpful for writing implementation classes for listener interfaces in graphics programming.

What is the syntax for writing an anonymous class?

The syntax is: new Type() { [fields] [methods] }.

What do we need in order to create anonymous classes?

An interface. Signup and view all the answers

What is required in order to implement a lambda method?

Lambda methods require an interface that declares only one method. Signup and view all the answers

Give an example of an implemented lambda method.

An example is <code>interface Op { public abstract int apply(int a, int b); } Op add = ((a, b) -> a + b);</code>. Signup and view all the answers

What is a functional interface?

A functional interface is an interface that has just one abstract method, representing a single function contract. Signup and view all the answers

When should we use method references / anonymous classes over lambda methods?

If it is necessary for a lambda expression to refer to itself (via this), then a method reference or anonymous class should be used instead. Signup and view all the answers

Can we use default methods in functional interfaces?

True Signup and view all the answers

Why do lambda expressions require a functional interface?

A Functional Interface serves as a data type for lambda expressions. Signup and view all the answers

Study Notes

Anonymous Classes

An anonymous class is an inner class without a name, used to create a single object.
Only one instance exists and is typically declared within a method.
An anonymous class is constructed immediately and returns an instance to the caller.
Useful for implementing listener interfaces in graphics programming and overloading methods without subclassing.

Syntax of Anonymous Classes

The syntax for an anonymous class is:
```
new Type() {
  [fields]
  [methods]
}
```

Requirements for Creating Anonymous Classes

An interface must be defined to create anonymous classes.

Lambda Methods

Lambda methods require an interface that declares only one method (functional interface).
The syntax for a lambda expression is:
```
(arg1[, arg2...]) -> functionBody
```

Example of Lambda Method Implementation

Example of implementing a lambda method:

interface Op {
  public abstract int apply(int a, int b);
}
Op add = ((a, b) -> a + b);

Functional Interfaces

A functional interface contains just one abstract method, representing a single function contract.
Functional interfaces serve as data types for lambda expressions.

Method References and Anonymous Classes

If a lambda expression needs to refer to itself (using this), it is better to use a method reference or an anonymous class.

Default Methods in Functional Interfaces

Default methods can be included in functional interfaces but cannot be used within lambda expressions directly.
Lambda expressions can be utilized within default methods of functional interfaces.

Description

Explore key concepts of lambda methods and anonymous classes through these flashcards. Learn about the properties and functionalities of anonymous classes and how they are useful in programming. Perfect for anyone looking to strengthen their understanding of these advanced Java topics.