Java Vector Examples

Use the Vector type, from java.util.Vector. Vector is a resizable, thread-safe array.

Vector. On the cavern floor a stalagmite builds up. As millennia pass it increases in height. The progress (though slow) shows growth.

Like the stalagmite, a Vector object in Java can grow. With add() we add elements. Usually a Vector is not placed in a cave (but it could be). Vector is found in java.util.Vector.

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.

Diamonds: The right side of the Vector declaration uses diamond inference syntax. The "Integer" type is inferred by the compiler.

Java program that uses Vector 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); } } } Output 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.

Java program that uses get 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); } } } Output 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.

Java program that uses set, setElementAt 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)); } } Output 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.

Size: Finally we use the size() method on the Vector. Three elements (Strings) are stored within the collection.

Strings

Java program that adds ArrayList to 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()); } } Output 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.Array

Java program that converts Vector, array 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); } } } Output 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).

Java program that uses contains, indexOf 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); } } Output 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.ArrayList

Version 1: This version of the code adds Integers to an ArrayList in a tight loop.

Version 2: Here we do the same thing as in version 1, but use a Vector instead. We call add() on the Vector instance.

Result: The ArrayList, which is not thread-safe, is about twice as fast as Vector when adding many elements.

Thus: Replacing Vector with ArrayList will likely lead to a performance increase in programs.

Java program that benchmarks ArrayList, 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); } } Output 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.Sort: Collections.sort

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.Stack

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.

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Java Vector Examples

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