To add values to a Java List there are numerous ways. We will discuss it one by one in detail.
- Insert elements using the list add method
- Convert Arrays to List
- Get input from other sources and add it to list
Add values using Arrays.asList
//Add Numbers
List<Integer> numbers = Arrays.asList(1, 5, 4, 3, 2);
//Add Strings
List<String> strings = Arrays.asList("Java", "First", "Hello", "World", "Program");
//Add Object
List<Item> items = Arrays.asList(
new Item("Pen"),
new Item("Paper"),
new Item("Pencil"));
Add Elements to the List
Elements are added to the list using add() method.
//Add Numbers
List<Integer> numbers = new ArrayList();
numbers.add(1);
numbers.add(5);
numbers.add(4);
numbers.add(3);
numbers.add(2);
//Add Strings
List<String> strings = new ArrayList();
strings.add("Java");
strings.add("First");
strings.add("Hello");
strings.add("World");
strings.add("Program");
//Add Object
List<Item> items = new ArrayList();
items.add(new Item("Pen"));
items.add(new Item("Paper"));
items.add(new Item("Pencil"));
The constructor Integer(int) is deprecated. So I added numbers.add(1) instead of numbers.add(new Integer(1)) .
Convert Integer Array to List
When the input is an array of integer values it can be converted to a list.
Integer[] intValues = new Integer[]{ 1, 3, 2 };
List<Integer> numbers = Arrays.asList(intValues);
Convert String Array to List
When the input is an array of strings it is converted to a list.
String[] strValues = new String[]{ "List", "Insert", "Values" };
List<String> strings = Arrays.asList(strValues);
Add Elements To Specific Index
The add method takes index and element as two arguments. The elements can be added to a specific index.
//Add Numbers to index
List<Integer> numbers = new ArrayList();
numbers.add(0,1); // start with 0 index
numbers.add(5);
numbers.add(4);
numbers.add(2,3); //add to 2 index position
numbers.add(2);
The elements are printed according to inserted index position. The index starts with 0 (zero). Value 3 is inserted in the 2nd index.
1
5
3
4
2
Complete Code
public class Item {
String itemName;
public Item(String itemName) {
super();
this.itemName = itemName;
}
// setter/getter
}
package com.digitizedpost.list;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class ListInsertElement {
private void addValues() {
//Add Numbers
List<Integer> numbers = Arrays.asList(1, 5, 4, 3, 2);
for(Integer number : numbers) {
System.out.println(number);
}
//Add Strings
List<String> strings = Arrays.asList("Java", "First", "Hello", "World", "Program");
for(String string : strings) {
System.out.println(string);
}
//Add Object
List<Item> items = Arrays.asList(
new Item("Pen"),
new Item("Paper"),
new Item("Pencil"));
for(Item item : items) {
System.out.println(item.getItemName());
}
}
private void addElements() {
//Add Numbers
List<Integer> numbers = new ArrayList();
numbers.add(1);
numbers.add(5);
numbers.add(4);
numbers.add(3);
numbers.add(2);
for(Integer number : numbers) {
System.out.println(number);
}
//Add Strings
List<String> strings = new ArrayList();
strings.add("Java");
strings.add("First");
strings.add("Hello");
strings.add("World");
strings.add("Program");
for(String string : strings) {
System.out.println(string);
}
//Add Object
List<Item> items = new ArrayList();
items.add(new Item("Pen"));
items.add(new Item("Paper"));
items.add(new Item("Pencil"));
for(Item item : items) {
System.out.println(item.getItemName());
}
}
private void addFromOtherSource() {
//From Integer Array. When the input is a integer array
Integer[] intValues = new Integer[]{ 1, 3, 2 };
List<Integer> numbers = Arrays.asList(intValues);
for(Integer number : numbers) {
System.out.println(numbers);
}
//From String Array. When the input is a string array
String[] strValues = new String[]{ "List", "Insert", "Values" };
List<String> strings = Arrays.asList(strValues);
for(String string : strings) {
System.out.println(string);
}
}
private void addElementsToSpecificIndex() {
//Add Numbers to index
List<Integer> numbers = new ArrayList();
numbers.add(0,1); // start with 0 index
numbers.add(5);
numbers.add(4);
numbers.add(2,3); //add to 2 index position
numbers.add(2);
for(Integer number : numbers) {
System.out.println(number);
}
}
public static void main(String[] args) {
new ListInsertElement().addValues();
new ListInsertElement().addElements();
new ListInsertElement().addFromOtherSource();
new ListInsertElement().addElementsToSpecificIndex();
}
}