Interview Q&A / Java
Java interview questions
Collections, the JVM, strings, exceptions and threads, the backbone of most campus placement rounds.
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- What is a functional interface in Java and which built-in ones should you know?
A functional interface has exactly one abstract method, so a lambda can implement it. Core ones are Predicate (test), Function (apply), Consumer (accept) and Supplier (get). @FunctionalInterface makes the compiler check the rule.
BeginnerQuick answer1 min read - What is a lambda expression in Java and where can you use it?
A lambda is a short anonymous function written as (parameters) -> body. It can be used wherever a functional interface, an interface with exactly one abstract method, is expected, such as Runnable, Comparator or Predicate.
BeginnerQuick answer1 min read - What is a method reference in Java and when would you use it instead of a lambda?
A method reference is a shorthand like String::length for a lambda that only calls one existing method. It makes code shorter and clearer when the lambda adds nothing beyond that call.
BeginnerQuick answer1 min read