In this article we are going see what is Java Vector, why do we use Vector in java and its commonly used methods with simple examples.
1. What is Vector in Java?
The Vector is a collections class that implements a growable array of objects. Like an array, it contains components that can be accessed using an integer index
Vectoris a legacy collections class injava.utilpackage.Vectorclass is used to hold a group of elements and it is one of the implementation class forListinterface.
1.1. Vector features :
- The underlying data structure is resizable array (or) growable array.
- Duplicate objects are allowed.
- Insertion order is preserved ( means ordered).
- Heterogeneous objects are allowed (non generic version).
- Null insertion is possible.
- Implements Serializable, Cloneable and RandomAccess interfaces.
- Every method present in Vector is synchronized and hence Vector is Thread safe.
1.2. Why do we use Vector?
ArrayList has the similar features but not synchronized it’s operations. All Vector operations are synchronized, so whenever thread safety required to hold collection of elements and elements insertion order is required, Vector is good choice over ArrayList. ArrayList is faster if since it is non-synchronized. If we don’t have any explicit requirements for using either of them, we use ArrayList over Vector.
2. Create a Vector instance
Vector class provides following constructors to create a Vector instance.
//Constructs an empty vector so that its internal data array has size 10. //incremental capacity zero Vector v = new Vector(); //Constructs an empty vector with the specified initial capacity //incremental capacity zero Vector v = new Vector(int initialCapacity); //Constructs an empty vector with the specified initial capacity and capacity increment. Vector v = new Vector(int initialCapacity, int incrementalCapacity); //Can be used to convert other collection object to Vector Vector v = new Vector(Collection c);
3. Adding elements to Vector
public class JavaVectorAddElementsDemo {
public static void main(String[] args) {
Vector<String> v = new Vector<>();
// adding single element
v.add("Peter");//Collection interface method
v.addElement("Martin");//Vector Specific method
v.add(2, "Mike");//List specific method
System.out.println(v);
}
}
Output :
[Peter, Martin, Mike]
4. Retrieve or Get elements from Vector
public class JavaVectorGetElementsDemo {
public static void main(String[] args) {
Vector<String> v = new Vector<>();
v.addElement("Peter");
v.addElement("Martin");
v.addElement("Mike");
System.out.println(v.firstElement());//Peter
System.out.println(v.lastElement());//Mike
System.out.println(v.get(1));//Martin
System.out.println(v.elementAt(1));//Martin
}
}
Output :
Peter Mike Martin Martin
5. Update elements in Vector
public class JavaVectorUpdateElementsDemo {
public static void main(String[] args) {
Vector<String> v = new Vector<>();
v.addElement("Peter");
v.addElement("Martin");
v.addElement("Mike");
System.out.println(v.set(2, "Ashja"));//Mike - returns old
v.setElementAt("Anand", 1);
System.out.println(v);//[Peter, Anand, Ashja]
}
}
Output :
Mike [Peter, Anand, Ashja]
6. Remove elements from Vector
public class JavaVectorRemoveElementsDemo {
public static void main(String[] args) {
Vector<String> v = new Vector<>();
v.addElement("Peter");
v.addElement("Martin");
v.addElement("Mike");
v.addElement("Anand");
v.addElement("Ashja");
v.addElement("John");
v.removeElement("John");
System.out.println(v);//[Peter, Martin, Mike, Anand, Ashja]
v.removeElementAt(2);
System.out.println(v);//[Peter, Martin, Anand, Ashja]
v.remove("Martin");
System.out.println(v);//[Peter, Anand, Ashja]
v.removeIf(name -> name.contains("A"));
System.out.println(v);//[Peter]
v.removeAllElements();
System.out.println(v);//[]
}
}
Output :
[Peter, Martin, Mike, Anand, Ashja] [Peter, Martin, Anand, Ashja] [Peter, Anand, Ashja] [Peter] []
7. Iterate Vector elements
There are several ways to iterate Java Vector, in this example demonstrating how we iterate Vector using Enumeration with elemetnts() of Vector class.
public class JavaVectorIterateElementsDemo {
public static void main(String[] args) {
Vector<String> v = new Vector<>();
v.addElement("Peter");
v.addElement("Martin");
v.addElement("Mike");
v.addElement("Anand");
v.addElement("Ashja");
v.addElement("John");
System.out.println("---- Iterate using Enumeration ----");
Enumeration<String> enumeration = v.elements();
while (enumeration.hasMoreElements())
System.out.println(enumeration.nextElement());
System.out.println("---- Iterate using Stream.forEach() ----");
v.stream().forEach(name -> System.out.println(name));
System.out.println("---- Iterate using enhanced for-each loop ----");
for(String name : v)
System.out.println(name);
System.out.println("---- Iterate using java 8 forEach() ----");
v.forEach(name -> System.out.println(name));
}
}
Output :
---- Iterate using Enumeration ---- Peter Martin Mike Anand Ashja John ---- Iterate using Stream.forEach() ---- Peter Martin Mike Anand Ashja John ---- Iterate using Stream.forEach() ---- Peter Martin Mike Anand Ashja John ---- Iterate using java 8 forEach() ---- Peter Martin Mike Anand Ashja John
8. Filter Vector elements
Since java 8, we can apply Stream operations to collections implementation classes.
public class JavaVectorFilterElementsDemo {
public static void main(String[] args) {
Vector<String> v = new Vector<>();
v.addElement("Peter");
v.addElement("Martin");
v.addElement("Mike");
v.addElement("Anand");
v.addElement("Ashja");
v.addElement("John");
v.stream().filter(name -> name.startsWith("A"))
.forEach(name -> System.out.println(name));
}
}
Output :
Anand Ashja
Conclusion :
In this article we have covered what is Vector class in Java, when do we use it, the key features of Vector class, creating and iterating a vector and its other common methods with the examples.
