Java ArrayList add method

Java ArrayList add(E element) method

The ArrayListadd(E element) methodof Java ArrayList classappends a new value to the end of this list.

Syntax:

Parameter:

Here, "element" is an element to be appended to the list.

Return:

It always return "true". Don't worry about the Boolean return value. It always there as other classes in the collections family need a return value in the signature when adding an element.

Example 1

import java.util.ArrayList;
public class ArrayListAddExample1{
public static void main(String[] args) {
ArrayList list = new ArrayList();
list.add("element1");	// [element1]
list.add(Boolean.TRUE);	// [element1, true]
list.add("last element")	// [element1, true, last element]
System.out.println(list);	// [element1, true, last element]
}
}

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Output:

[element1, true, last element]

Example 2

import java.util.ArrayList;
public class ArrayListAddExample2{
public static void main(String[] args){
ArrayList<Integer> id = new ArrayList<>();
list.add(1); // [1]
list.add("student id");	// does not compile 
}
}

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Output:

does not compile.

This time the compiler knows that only Integer values are allowed in and prevents the attempt to add a String value.

Java ArrayList add(int index, E element) method

The add(int index, E element) method of Java ArrayList class inserts a specific element in a specific index of ArrayList. It shifts the element of indicated index if exist and subsequent elements to the right.

Syntax:

Parameter:

"index": index at which the element will be inserted.

"element": is an element to be inserted.

Return:

Return nothing.

Example 3

import java.util.ArrayList;
public class ArrayListAddExample3{
public static void main(String[] args){
List<String> colors = new ArrayList<>();
colors.add("red");		// ["red"]
colors.add("blue");		// ["red" , "blue"]
colors.add(1, "white");	// ["red" , "white", "blue"]
colors.add(0, "black");	// ["black", "red" , "white", "blue"]
System.out.println(colors);	// ["black", "red" , "white", "blue"]
}
}

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Output:

["black", "red" , "white", "blue"]

Example 4

import java.util.ArrayList;
public class ArrayListAddExample4{
public static void main(String[] args){
List<Object> list = new ArrayList<>();
list.add(0, "e1");		// ["e1"]
list.add(1);			// ["e1" , 1]
list.add(1, "e2");		// ["e1", "e2", 1]
list.add(0, 1);			// [1, "e1", "e2" , 1]
System.out.println(list);	// [1, "e1", "e2" , 1]
}
}

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Output:

[1, "e1", "e2" , 1]

Example 5

import java.util.ArrayList;
public class ArrayListAddExample5{
public static void main(String[] args){
List<Object> list = new ArrayList<>();
list.add(0, "element1");	// ["element1"]
list.add(1, "element2");	// ["element1", "element2"]
list.add(3, "element2");	// throws IndexOutOfBoundsException
}
}

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Output: