ArrayList contains() method is used to check if the specified element exists in the given arraylist or not. If element exist then method returns true, else false.
1. ArrayList contains() syntax
The contains() method is pretty simple. It simply checks the index of element in the list. If the index is greater than '0' than element is present in the list.
public boolean contains(Object o) {
return indexOf(o) >= 0;
}
2. ArrayList contains() example to check element exists
In given Java program, we have few alphabets stored in the arraylist. We will try to find out if letter “A” and “Z” are present in the list or not.
public class ArrayListExample
{
public static void main(String[] args)
{
ArrayList<String> list = new ArrayList<>(2);
list.add("A");
list.add("B");
list.add("C");
list.add("D");
System.out.println( list.contains("A") ); //true
System.out.println( list.contains("Z") ); //false
}
}
Program output.
true false
3. ArrayList indexOf() example to check if element exists
As noted above, contains() method uses indexOf() method to determine if a specified element is present in the list or not. So we can also directly use the indexOf() method to check the existance of any supplied element value.
public class ArrayListExample
{
public static void main(String[] args)
{
ArrayList<String> list = new ArrayList<>(2);
list.add("A");
list.add("B");
list.add("C");
list.add("D");
System.out.println( list.indexOf("A") > 0 ); //true
System.out.println( list.indexOf("Z") > 0); //false
}
}
Program output.
true false
Happy Learning !!
Read More:
A Guide to Java ArrayList
ArrayList Java Docs