Vector

This Java collection is similar to the ArrayList. It will resize to accommodate more elements. We call add() to place elements at the end.

A warning

Vector, which is part of java.util.Vector, is not the most optimized list collection in Java. It is fine for older code, but new code should use ArrayList.

Add, for-loop

This program shows the basic syntax for Vector. It adds 2 Integers to an Integer Vector. It then uses the for-loop to display those elements to the console.

import java.util.Vector;

public class Program {
    public static void main(String[] args) {

        // Add two values to Vector.
        Vector<Integer> v = new Vector<>();
        v.add(100);
        v.add(1000);

        // Display values.
        for (int value : v) {
            System.out.println(value);
        }
    }
}
100
1000

Get element

We access elements in a Vector with the get() method. And with a for-loop, we can call get() on all indexes. This accesses every element in the Vector.

import java.util.Vector;

public class Program {
    public static void main(String[] args) {

        Vector<Integer> v = new Vector<>();
        v.add(20);
        v.add(30);
        v.add(40);

        // ... Get element 0.
        System.out.println(v.get(0));

        // ... Loop over all indexes, calling get.
        for (int i = 0; i < v.size(); i++) {
            int value = v.get(i);
            System.out.println(value);
        }
    }
}
20
30
40

Set element

Set() assigns an element value at an index within the vector. It returns the value of the old, replaced element. SetElementAt is an older method—its arguments are reversed.

import java.util.Vector;

public class Program {
    public static void main(String[] args) {

        // Create one-element Vector.
        Vector<Integer> v = new Vector<>();
        v.add(20);

        // Set index 0.
        int old = v.set(0, 30);

        // Display old and current value.
        System.out.println(old);
        System.out.println(v.get(0));

        // Set index 0 with setElementAt.
        v.setElementAt(40, 0);
        System.out.println(v.get(0));
    }
}
20
30
40

AddAll, ArrayList

Here we add the contents of an ArrayList to a Vector. We add three elements to ArrayList. Then we call addAll to add them to our Vector.

import java.util.ArrayList;
import java.util.Vector;

public class Program {
    public static void main(String[] args) {

        // Create new ArrayList.
        ArrayList<String> values = new ArrayList<>();
        values.add("cat");
        values.add("dog");
        values.add("mouse");

        // Add ArrayList to Vector.
        Vector<String> v = new Vector<String>();
        v.addAll(values);

        // Display size of Vector.
        System.out.println(v.size());
    }
}
3

Convert Vector to array

Suppose we have a Vector, but want an array. With the toArray method, this conversion is easily done. The empty String array is allocated and filled.

import java.util.Vector;

public class Program {
    public static void main(String[] args) {

        // Add ArrayList to Vector.
        Vector<String> v = new Vector<>();
        v.add("one");
        v.add("two");
        v.add("three");

        // ... Convert Vector into String array.
        String[] array = {};
        String[] result = v.toArray(array);
        for (String value : result) {
            System.out.println(value);
        }
    }
}
one
two
three

Search

With contains and indexOf we search a Vector. Contains returns true if the specified element exists. IndexOf meanwhile returns the element's index (or negative one if not found).

import java.util.Vector;

public class Program {
    public static void main(String[] args) {

        Vector<Integer> v = new Vector<>();
        v.add(5);
        v.add(10);
        v.add(15);
        v.add(20);

        // See if 15 is present.
        if (v.contains(15)) {
            System.out.println("Contains 15");
        }

        // Get index of value 20.
        int index = v.indexOf(20);
        System.out.println("index of 20 = " + index);
    }
}
Contains 15
index of 20 = 3

Benchmark, vector

Consider the Vector: the most similar collection in Java is the ArrayList. Here we benchmark an ArrayList against a Vector.

import java.util.ArrayList;
import java.util.Vector;

public class Program {
    public static void main(String[] args) {

        long t1 = System.currentTimeMillis();

        // Version 1: add to ArrayList.
        ArrayList<Integer> a = new ArrayList<>();
        for (int i = 0; i < 100000; i++) {
            a.add(i);
        }

        long t2 = System.currentTimeMillis();

        // Version 2: add to Vector.
        Vector<Integer> v = new Vector<>();
        for (int i = 0; i < 100000; i++) {
            v.add(i);
        }

        long t3 = System.currentTimeMillis();

        // ... Times.
        System.out.println(t2 - t1);
        System.out.println(t3 - t2);
    }
}
 5 ms, ArrayList
10 ms, Vector

Sort

We sort a Vector by passing it to the Collections.sort method, found in java.util.Collections. The Vector is sorted in-place. By default the sorting order is ascending.

Stack

In the Stack collection, a LIFO (last-in-first-out) algorithm is used. Stack is based on Vector: for this reason it is deprecated.

In programs with threads, a Vector may be a better choice than ArrayList. And Vector is used in older programs that precede ArrayList. Removing Vector is often an optimization.