What is the Builder design pattern in Java?
Why Interviewers Ask This
Interviewers ask this to evaluate whether you have the depth of knowledge needed to mentor others and lead technical decisions. The expected answer goes beyond definitions into practical implications and real-world consequences.
Answer
The Builder pattern separates the construction of a complex object from its representation, allowing the same construction process to create different representations. It is especially useful when an object has many optional parameters — it avoids telescoping constructors and the mutable JavaBean approach. A Builder class has methods for each parameter (returning this for chaining) and a build() method that creates the final immutable object. Example: new Pizza.Builder("large").addTopping("cheese").addTopping("mushroom").build(). Lombok's @Builder annotation generates Builder code automatically. The Builder pattern is used extensively in Java APIs — StringBuilder, ProcessBuilder, and HttpClient.Builder are all examples.
Pro Tip
If you're unsure about a detail, say so honestly and explain your reasoning. Interviewers respect candidates who can think through uncertainty rather than bluffing.
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