Master Java Generics in 3 Hours

Explore how generics replace object fields with a type parameter in a generic pair, ensuring type safety, avoiding casts, and clarifying type parameter naming conventions.

Learn how to instantiate and use generic types in Java by creating generic pairs, exploring type inference with the diamond operator, and using records for immutable generics.

Understand raw types in Java and their role for backward compatibility with non-generic code. Learn how raw types risk runtime casts and errors, and why prefer parameterized types.

Use bounded type parameters to restrict generics to number subclasses, enabling number methods like doubleValue in a mutable number pair with integers, floats, and big decimals.

Design generic types with multiple parameters, such as a key value pair using K and V. Apply bounds like extends number and comparable to enable key comparisons and intersectional types.

Learn java generics by using method-level generics to write a single sum method for numbers and a bounded key greater method for key-value pairs, returning an optional result.

See how a generic method accepts lists of any number type, with T inferred as integer, float, or big decimal, and can be explicitly specified via angle brackets.

Explore the inheritance dilemma in Java generics, contrasting parameterized types with list-based approaches. Understand how List<Integer> is not a subtype of List<Number>, causing compile errors and guiding proper type inference.

Extend a type parameter with another type parameter using generics, illustrated by a mutable pair and a copy from method that accepts pairs of any type that extends T.

Explore how Java generics implement type erasure, erasing parameterized types to object while preserving type safety via compiler-inserted casts, and understand implications for static members and bounds.

Explore unbounded wildcards in Java generics, using the question mark to print lists of any type while retrieving elements as objects. You can't add elements to a wildcard list.

Explore how upper bound wildcards enable general, type-safe list operations by treating elements as numbers or subtypes, improving compactness over generic methods.

Explore the upper bounded wildcard hierarchy and is-a relationships in generic classes like mutable pair, then determine assignment validity and safe usage of wildcards in Java.

Explore the generic method versus wild card approaches for parameter dependencies, illustrated by a mutable pair reset example and type inference that lets numbers and objects work together.

Explore how lower bounded wildcards use the super keyword to accept any supertype, enabling flexible methods like reset to zero for mutable pairs, and compare with upper bounds.

Explore when to use wildcard generics in Java, guided by the producer extends consumer super rule, with examples from collection methods like add all, contains all, copy, and binary search.

Discover how wildcard capture enables type-safe element swapping in Java generics, using a private generic helper to avoid raw types and unchecked warnings.

Compare Java arrays and generics: arrays are covariant and runtime reified, while generics are invariant and erased at compile time. Use generics wisely with wildcards for type safety.

Wrap up by highlighting how to apply Java generics in projects, and point to the Java docs for the collections framework, streams, and completable futures for deeper learning.

Explore nested classes in Java, comparing static nested classes with inner non-static ones, showing when a child can access the parent's members and how the compiler adds a parent reference.

Learn how Java records model immutable data with automatic getters and methods. Discover canonical constructors, defensive copies for collections, and nested records in Java 16 and beyond.

Discover how Java intersection types combine multiple interfaces into a single inferred type, using examples with number and comparable, switch expressions, and var to preserve the intersection in code.

Learn the basics of the Java Optional class, create optionals with of, empty, and ofNullable, and safely consume them with isPresent and get to avoid null pointer errors.

Explore the fluent, functional use of Java Optional with map, filter, and flatMap, including if present, or else, or else get, and or else throw to write robust, readable code.

Explore the optional.stream method and its integration with Java streams, using map, filter, and flatMap to extract addresses from a list of users.