Java - Deprecated

Java maintains backwards compatibility, but legacy APIs, obsolete runtime modules, and outdated patterns are progressively deprecated and removed.

Officially Deprecated / Removed APIs

Security Manager (JEP 411): Deprecated for removal in Java 17. Blocked or issues warnings in Java 21+. Modern security relies on OS containers, hypervisors, and process isolation rather than Java sandbox security managers.
Finalization (Object.finalize(), JEP 421): Deprecated for removal in Java 18. Use try-with-resources (AutoCloseable) or java.lang.ref.Cleaner instead.
Thread Management Methods: Thread.stop(), Thread.suspend(), and Thread.resume() have been permanently disabled and throw UnsupportedOperationException.
Applet API & Java Web Start: Deprecated in Java 9, removed completely from JDK 11.
Nashorn JavaScript Engine: Removed in Java 15 (JEP 372).
JavaFX: Removed from the core JDK in Java 11; distributed independently as OpenJFX.
RMI Activation: Deprecated for removal in Java 15 and removed in Java 17.

Removed in Java 11 (JEP 320):

java.xml.ws (JAX-WS)
java.xml.bind (JAXB) — modern projects use external Maven/Gradle dependencies (e.g. jakarta.xml.bind:jakarta.xml.bind-api).
java.corba (CORBA)
java.transaction (JTA)

Concurrent Mark Sweep (CMS): Deprecated in Java 9, removed in Java 14 (JEP 363). Replace with G1GC (default) or ZGC (-XX:+UseZGC -XX:+ZGenerational).

Legacy Class / Pattern	Modern Java Replacement	Rationale
`java.util.Date`, `Calendar`	`java.time.Instant`, `LocalDate`, `ZonedDateTime`	`Date`/`Calendar` are mutable, not thread-safe, and zero-indexed for months. `java.time` is immutable and ISO-8601 compliant.
`java.util.Vector`	`java.util.ArrayList`	`Vector` synchronizes every method, creating massive thread contention.
`java.util.Stack`	`java.util.ArrayDeque`	`Stack` inherits from `Vector`; `ArrayDeque` is faster and not synchronized.
`java.util.Hashtable`	`java.util.concurrent.ConcurrentHashMap`	`Hashtable` uses coarse whole-map synchronization; `ConcurrentHashMap` uses fine-grained lock-striping.
Raw Threads (`new Thread()`)	`Executors.newVirtualThreadPerTaskExecutor()`	Virtual threads (Java 21) or thread pools avoid heavy OS thread allocation overhead.
Anonymous Classes for Single Methods	Lambda expressions (`x -> ...`) / Method references	Lambdas reduce boilerplate and compile to `invokedynamic` rather than generating `.class` files.
Plain POJO data carriers	`record` classes (Java 14+)	Auto-generates immutable constructors, getters, `equals()`, `hashCode()`, and `toString()`.
Complex getter chains with null checks	`Optional<T>`	Eliminates `NullPointerException` risks on method return values.