Java ArrayList example

abstract

Java class ArrayList(java.util.ArrayList) is a fast and easy to use class representing one-dimensional array. ArrayList is not synchronized i.e. using it in more that one thread may cause problems.

compatible

Sun Java 1.5 or higher (because this example uses generics)

ArrayList class provides methods for basic array operations:

add( Object o ) - puts reference to object into ArrayList
get( int index ) - retrieves object reference from ArrayList index position
size() - returns ArrayList size
remove( int index ) - removes the element at the specified position in this list. Shifts any subsequent elements to the left and returns the element that was removed from the list.
indexOf( Object o) - finds the index in this list of the first occurrence of the specified element
clear() - removes all of the elements

Following example ask user for his/her name, and suggests him/her a vacation place.

ArrayList "myarr" is filled with resort names(add method). After user enters his name, we calculate residue of division of user's name length by myarr size -- operation result is a number from 0 to myarr.size()-1 -- which is suitable as array index.

 
 
import java.io.BufferedReader; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.util.ArrayList; 
 
public class Ex01 { 
 
    public static void main(String[] args) throws IOException { 
 
        BufferedReader userInput = new BufferedReader 
            (new InputStreamReader(System.in));
 
        ArrayList<String> myArr = new ArrayList<String>();
        myArr.add("Italian Riviera");
        myArr.add("Jersey Shore");
        myArr.add("Puerto Rico");
        myArr.add("Los Cabos Corridor");
        myArr.add("Lubmin");
        myArr.add("Coney Island");
        myArr.add("Karlovy Vary");
        myArr.add("Bourbon-l'Archambault");
        myArr.add("Walt Disney World Resort");
        myArr.add("Barbados");
 
        System.out.println("Stupid Vacation Resort Adviser");
        System.out.println("Enter your name:");
        String name = userInput.readLine();
        Integer nameLength = name.length();
        if (nameLength == 0) 
        { 
            System.out.println("empty name entered");
            return;
        } 
 
        Integer vacationIndex = nameLength % myArr.size();
 
        System.out.println("\nYour name is "+name+", its length is " + 
                        nameLength + " characters,\n" +
                        "that's why we suggest you to go to " 
                        + myArr.get(vacationIndex));
    } 
}

warning

ArrayList stores only object references. That's why, it's impossible to use primitive data types like double or int. Use wrapper class (like Integer or Double) instead.

For multi-theaded(synchronized) array class use Vector (java.lang.Vector)

tested

JDK 1.5