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Resize an array using ArrayList - WikiJava
Thursday, 30th October 2014
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Resize an array using ArrayList

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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

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