Which version of Java introduced lambda expressions?

Which version of Java introduced lambda expressions? The answer is Java 8. Released in 2014, Java 8 added lambda expressions as part of Project Lambda and JSR 335.

A lambda provides a compact way to represent behavior that can be passed as a value, for example `x -> x * 2`. Java’s lambdas are closely tied to functional interfaces: interfaces with one abstract method, such as `Runnable`, `Comparator`, and the interfaces in `java.util.function`. The compiler uses the target interface type to determine what a lambda means.

Java 8 also introduced method references, default interface methods, and the Stream API, which made lambdas especially useful for collection processing. Lambdas did not turn Java into a purely functional language; Java remains object-oriented and supports mutable state, classes, inheritance, and traditional anonymous classes. Later releases added features such as local-variable type inference and records, but lambda expressions themselves date to Java 8.