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Java ArrayList toString

Submitted by Sameera on Fri, 11/12/2010 - 19:40

This Java example shows how to use Java ArrayList toString method to display its elements.

import java.util.ArrayList;
 
//Java ArrayList toString
public class JavaArrayListToString {
    
    public static void main(String args[]){
       
        ArrayList<Integer> aListNumbers = new ArrayList<Integer>();
        aListNumbers.add(1);
        aListNumbers.add(2);
        aListNumbers.add(3);
       
        /*
         * This will call toString method of Java ArrayList, which in turn
         * calls toString method of Integer wrapper class.
         *
         * toString method of Integer wrapper class outputs underlying int
         * value.
         */
        System.out.println(aListNumbers);
 
        //Create objects of custom Person class
        Person p1 = new Person("Alex", 29);
        Person p2 = new Person("Tanya", 21);
       
        //Create an ArrayList of objects Person
        ArrayList<Person> aListPersons = new ArrayList<Person>();
       
        //add Objects of Persons to ArrayList
        aListPersons.add(p1);
        aListPersons.add(p2);
       
        /*
         * This will call toString method of ArrayList class and in turn
         * it will call toString method of underlying class, that is in this
         * case Person class.
         *
         * If the Person class does not have toString defined, toString method
         * of Object class is called which prints default output similar to
         * as shown below.
         *
         * [Person@1c161c16, Person@1c1c1c1c]
         *
         * This kind of output is not useful, as we expect it to print
         * name and age of person added to ArrayList. In this case we can
         * override toString method of Person class.
         *
         */
        System.out.println(aListPersons);
       
    }
}
 
class Person{
    
    String name;
    int age;
    
    public Person(String name, int age){
        this.name = name;
        this.age = age;
    }
    
    public String getName(){
        return this.name;
    }
    
    public int getAge(){
        return this.age;
    }
    
    public String toString(){
        return this.getName() + "-" + this.getAge();
    }
    
}
 
/*
Output of above given Java ArrayList toString method would be
[Alex-29, Tanya-21]
[1, 2, 3]
*/