Browse Clojure Foundations for Java Developers

Vectors

Fuad Efendi

Clojure’s default ordered collection: persistent vectors with fast indexed access, assoc updates, and conj at the end.

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Vectors are Clojure’s default choice for ordered data. They’re persistent (immutable with structural sharing) and provide fast indexed access—similar to an immutable ArrayList.

Create

1[1 2 3]
2(vector 1 2 3)

Read (Indexed)

1(def v [10 20 30])
2
3(get v 1)   ; => 20
4(nth v 1)   ; => 20
5(v 1)       ; => 20  ; vector-as-function lookup

Update and Grow

1(assoc [10 20 30] 1 99) ; => [10 99 30]
2(conj  [1 2] 3)         ; => [1 2 3]   ; vectors conj at the end

Stack-Like Ops (peek / pop)

1(peek [1 2 3]) ; => 3
2(pop  [1 2 3]) ; => [1 2]

Slice with subvec

1(subvec [0 1 2 3] 1 3) ; => [1 2]

subvec uses start/end indexes and the end is exclusive (like Java’s substring and many slice APIs).

Knowledge Check: Vectors

### What does `(peek [1 2 3])` return? - [x] `3` - [ ] `1` - [ ] `[1 2]` - [ ] `nil` > **Explanation:** `peek` returns the “top” element for the collection. For vectors, that’s the last element. ### What does `(conj [1 2] 3)` evaluate to? - [x] `[1 2 3]` - [ ] `(3 1 2)` - [ ] `[3 1 2]` - [ ] It mutates the vector and returns `nil`. > **Explanation:** `conj` adds at the most efficient place. For vectors, that’s the end. ### What does `(subvec [0 1 2 3] 1 3)` evaluate to? - [x] `[1 2]` - [ ] `[1 2 3]` - [ ] `[0 1 2]` - [ ] `(1 2)` > **Explanation:** `subvec` takes a start index (inclusive) and end index (exclusive) and returns a vector slice.
Revised on Friday, April 24, 2026
A.3.1 Lists
A.3.3 Maps