Tuesday, 22nd June 2010
The new frontier for learning Java

Resize an array using ArrayList

From WikiJava

Jump to: navigation, search


This example shows how to use an ArrayList to get a dynamic size array.

Contents

the article

Arrays cannot be resized dynamically. If you want a dynamic data structure with random access, you use a Collection (Map, ArrayList,...).

If you need to expand, you can use System.arraycopy() method to copy the content of an array to another one.

But a better way is to use a Vector or an ArrayList. ArrayList is roughly equivalent to Vector, except that it is unsynchronized.

ArrayListDemo.java 

import java.util.ArrayList;
 
public class ArrayListDemo {
  public static void main (String arg[]) {
    ArrayListDemo x = new ArrayListDemo();
    x.doit1();
    x.doit2();
  }
 
  public void doit1() {
    // single dimension
    ArrayList<String> list = new ArrayList<String>();
    list.add("a");
    list.add("b");
    int size = list.size();  // 2
    System.out.println("Array 1 " +list.get(0));   // a
  }
 
  public void doit2() {
    // multi dimensions
    ArrayList<ArrayList<String>> list = new ArrayList<ArrayList<String>>();
    ArrayList<String> l1 = new ArrayList<String>();
    l1.add("a");
    ArrayList<String> l2 = new ArrayList<String>();
    l2.add("b");
    ArrayList<String> l3 = new ArrayList<String>();
    l3.add("c");
 
    list.add(l1);
    list.add(l2);
    list.add(l3);
 
    int size1 = list.size();  // 3
    int size2 = list.get(0).size();  // 1
    System.out.println("Array 2 " 
      + list.get(1).get(0));   // b
    }
}

See Also

Resize an array, Real's Java How To

Comments from the users

To be notified via mail on the updates of this discussion you can login and click on watch at the top of the page


Title (required):

Website:

Comment:

Retrieved from "http://www.wikijava.org/wiki/Resize_an_array_using_ArrayList"