Java SE 11 Developer key terms

An automatic, lossless promotion of a smaller primitive to a larger compatible type, such as int to long or float to double, applied by the compiler without a cast.

An explicit conversion that may lose information or magnitude, such as long to int or double to float, requiring a cast operator and permitted between compatible primitive types.

The compiler's automatic wrapping of a primitive into its wrapper class, and unwrapping back, when a reference type is required; cached values apply for small integral and boolean ranges.

One of the immutable reference types such as Integer, Double, or Character that encapsulate a primitive value and provide parsing, conversion, and utility methods.

A reserved type name allowing local variable declarations whose type is inferred from the initializer; it cannot be used for fields, method parameters, or without an initializer.

A switch form that produces a value using arrow labels and yield, supports exhaustiveness for enums and strings, and avoids fall-through by default.

Execution continuing into subsequent case labels when a matched case lacks a break or return, a classic source of logic errors in colon-style switch statements.

A break statement followed by a label that exits the named enclosing loop or block, useful for escaping nested iteration in one step.

The ability of a supertype reference to invoke subclass-specific behavior through overridden methods, resolved at runtime by dynamic dispatch.

Runtime selection of the most specific overriding implementation based on the actual object type, not the declared reference type.

Declaring multiple methods with the same name but different parameter lists in one class; selection happens at compile time based on static argument types.

An override whose return type is a subtype of the overridden method's return type, permitted since Java 5 while parameter types must match exactly.

A class declared abstract that cannot be instantiated and may contain abstract methods that concrete subclasses must implement, plus shared state and behavior.

A method in an interface with a body marked default, allowing interfaces to evolve without breaking implementers; it is inherited but can be overridden.

A Throwable subtype other than RuntimeException and Error that the compiler requires to be caught or declared with throws.

A RuntimeException or Error subtype not enforced by the compiler; typically signals programming defects or unrecoverable conditions.

A try statement declaring resources that implement AutoCloseable and are closed automatically in reverse order, with suppressed exceptions attached when closing fails.

A statement using assert that tests an invariant and throws AssertionError when false; disabled by default and enabled with the -ea JVM option.

The rule that a String[] is assignable to Object[], which compiles but can throw ArrayStoreException at runtime when an incompatible element is stored.

A runtime exception thrown when an attempt is made to store an element of the wrong type into a covariant array reference.

The compiler's removal of generic type information so that parameterized types become raw types or bounds at runtime, preventing instanceof and array creation with type parameters.

A generic type argument written as ?, optionally bounded with extends or super, expressing unknown or restricted type families for flexible method signatures.

A generic interface defining compareTo for natural ordering, used by sorted collections and by Collections.sort and Arrays.sort.

A functional interface defining compare for external, customizable ordering, composable with thenComparing and reversed and usable with sorted stream operations.

A sequence consisting of a source, zero or more lazy intermediate operations, and one terminal operation that triggers traversal and produces a result.

A container that may hold a value or be empty, encouraging explicit handling of absence through methods such as map, flatMap, orElse, and ifPresent.

A compact lambda form written with double colons, such as String::length or System.out::println, referring to a static, instance, or constructor method.

An interface with exactly one abstract method, eligible for lambda expressions and method references, optionally annotated with @FunctionalInterface for compile-time checking.

The module-info.java file declaring a module's name, its required dependencies, exported packages, opened packages, and services it uses or provides.

A module declaration clause making a package's public types accessible to other modules; without it, types remain inaccessible even if public.

A requires clause marked transitive that re-exposes a dependency's exported packages to modules that read the declaring module.

Coordination of concurrent access using synchronized blocks or methods, locks, or atomic classes to guarantee visibility and mutual exclusion of shared mutable state.

A field modifier guaranteeing that reads and writes go to main memory with happens-before visibility, but without atomicity for compound operations.

A thread pool abstraction for submitting tasks, obtaining Futures, and shutting down gracefully; implementations come from the Executors factory methods.

An immutable, platform-independent representation of a file system location created with Paths.get or Path.of, supporting resolution and normalization operations.

A static helper offering operations such as readAllLines, write, copy, move, walk, and lines, throwing IOException on failure.

A character-input wrapper that buffers reads for efficiency and provides readLine for line-oriented processing of text streams.

A mechanism using ObjectInputFilter to restrict classes allowed during deserialization, mitigating gadget-chain attacks on untrusted data.

Checking and constraining external data before use, including length, range, and format checks, to prevent injection and unexpected state.

Granting only the permissions and access a component needs, applied in Java through security policies, module exports, and restricted file access.

An object identifying a language and region that drives formatting, parsing, and message selection; it is distinct from the default time zone.

An immutable formatter and parser for date-time values built from patterns or localized styles, with configurable locale and zone.

A container of locale-specific objects loaded by base name, falling back from specific to default locales, used for localizing messages.

An annotation meta-property controlling how long an annotation is kept: SOURCE discarded by the compiler, CLASS in bytecode only, or RUNTIME reflectively readable.

The @Target declaration restricting where an annotation may be applied, such as TYPE, METHOD, FIELD, PARAMETER, or a combination.