1. ArrayList get[] Method
ArrayList.get[int index] method returns the element at the specified position 'index' in the list.
1.1. Syntax
public Object get[ int index ];1.2. Method Parameter
index – index of the element to return. A valid index is always be between 0 [inclusive] to the size of ArrayList [exclusive].
For example, if ArrayList holds 10 objects then a valid argument index will be between 0 to 9 [both inclusive].
1.3. Return Value
The get[] method returns the reference of the object present at the specified index.
1.4. IndexOutOfBoundsException
An invalid index argument will cause IndexOutOfBoundsException error.
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 4, Size: 4 at java.util.ArrayList.rangeCheck[ArrayList.java:653] at java.util.ArrayList.get[ArrayList.java:429] at com.howtodoinjava.example.ArrayListExample.main[ArrayListExample.java:12]Method indexOf[] Signature
public int indexOf[Object o]
This method returns -1 if the specified element is not present in the list.
ArrayList get[index] Method in Java with Examples
The get[] method of ArrayList in Java is used to get the element of a specified index within the list.
Syntax:
get[index]Parameter:Index of the elements to be returned. It is of data-type int.
Return Type:The element at the specified index in the given list.
Exception:It throws IndexOutOfBoundsException if the index is out of range [index=size[]]
Note: Time Complexity: ArrayList is one of the List implementations built a top an array. Hence, get[index] is always a constant time O[1] operation.
Example:
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// Java Program to Demonstrate the working of
// get[] method in ArrayList
// Importing ArrayList class
import java.util.ArrayList;
// Main class
public class GFG {
// Main driver method
public static void main[String[] args]
{
// Creating an Empty Integer ArrayList
ArrayList arr = new ArrayList[4];
// Using add[] to initialize values
// [10, 20, 30, 40]
arr.add[10];
arr.add[20];
arr.add[30];
arr.add[40];
// Printing elements of list
System.out.println["List: " + arr];
// Getting element at index 2
int element = arr.get[2];
// Displaying element at specified index
// on console inside list
System.out.println["the element at index 2 is "
+ element];
}
}
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Example 2: Program to demonstrate the error
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// Java Program to Demonstrate Error Generated
// while using get[] method in ArrayList
// Importing ArrayList class
import java.util.ArrayList;
// Main class
public class GFG {
// Main driver method
public static void main[String[] args]
{
// Creating an Empty Integer ArrayList
ArrayList arr = new ArrayList[4];
// Using add[] method to insert elements
// and adding custom values
arr.add[10];
arr.add[20];
arr.add[30];
arr.add[40];
// Getting element at index 2
int element = arr.get[5];
// Print all the elements of ArrayList
System.out.println["the element at index 2 is "
+ element];
}
}
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Output :
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 5, Size: 4 at java.util.ArrayList.rangeCheck[ArrayList.java:657] at java.util.ArrayList.get[ArrayList.java:433] at GFG.main[GFG.java:22]Java.util.Arraylist.indexOf[] in Java
The indexOf[] method of ArrayList returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
Syntax :
public int IndexOf[Object o] obj : The element to search for.
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// Java code to demonstrate the working of
// indexOf in ArrayList
// for ArrayList functions
import java.util.ArrayList;
public class IndexOfEx {
public static void main[String[] args] {
// creating an Empty Integer ArrayList
ArrayList arr = new ArrayList[5];
// using add[] to initialize values
arr.add[1];
arr.add[2];
arr.add[3];
arr.add[4];
// printing initial value
System.out.print["The initial values in ArrayList are : "];
for [Integer value : arr] {
System.out.print[value];
System.out.print[" "];
}
// using indexOf[] to find index of 3
int pos =arr.indexOf[3];
// prints 2
System.out.println["\nThe element 3 is at index : " + pos];
}
}
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Output:
The initial values in ArrayList are : 1 2 3 4 The element 3 is at index : 2Practical Application : The index functions are mostly useful to determine last or first occurrence of events, for example last occurrence of 6 in a throw of a die, or 1st occurrence of any letter in a name etc.
One more example:
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// Java code to demonstrate the application of
// index functions in ArrayList
// for ArrayList functions
import java.util.ArrayList;
public class AppliIndex {
public static void main[String[] args] {
// creating an Empty Integer ArrayList
ArrayList arr = new ArrayList[10];
// using add[] to initialize dice values
arr.add[1];
arr.add[2];
arr.add[4];
arr.add[6];
arr.add[5];
arr.add[2];
arr.add[6];
arr.add[1];
arr.add[6];
arr.add[4];
// using IndexOf[] to find first index of 6
int pos1 =arr.indexOf[6];
// using lastIndexOf[] to find last index of 6
int pos2 =arr.lastIndexOf[6];
// to balance 0 based indexing
pos1 = pos1+1;
pos2 = pos2+1;
// printing first index of 6
System.out.println["The first occurrence of 6 is : " + pos1];
// printing last index of 6
System.out.println["The last occurrence of 6 is : " + pos2];
}
}
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Output:
The first occurrence of 6 is : 4 The last occurrence of 6 is : 9This article is contributed by Shambhavi Singh. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to . See your article appearing on the GeeksforGeeks main page and help other Geeks.
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