Java Collections Framework:ArrayList-5(Get/Search )

 

How to get sublist of an ArrayList with example

In this tutorial we will see how to get a sublist from an existing ArrayList. We will be doing it using the subList method of ArrayList class.

List subList(int fromIndex, int toIndex)

Here fromIndex is inclusive and toIndex is exclusive. There are few important points regarding this method which I have shared at the end of this post.

Example of getting sub-list from an ArrayList

Points to Note in the below example:
The subList method returns a list therefore to store the sublist in another ArrayList we must need to type cast the returned value in same way as I did in the below example. On the other side if we are storing the returned sublist into a list then there is no need to type cast (Refer the example).

package beginnersbook.com;
import java.util.ArrayList;
import java.util.List;
public class SublistExample {

 public static void main(String a[]){
     ArrayList<String> al = new ArrayList<String>();

     //Addition of elements in ArrayList
     al.add("Steve");
     al.add("Justin");
     al.add("Ajeet");
     al.add("John");
     al.add("Arnold");
     al.add("Chaitanya");

     System.out.println("Original ArrayList Content: "+al);

     //Sublist to ArrayList
     ArrayList<String> al2 = new ArrayList<String>(al.subList(1, 4));
     System.out.println("SubList stored in ArrayList: "+al2);

     //Sublist to List
     List<String> list = al.subList(1, 4);
     System.out.println("SubList stored in List: "+list);
  }
}

Output:

Original ArrayList Content: [Steve, Justin, Ajeet, John, Arnold, Chaitanya]
SubList stored in ArrayList: [Justin, Ajeet, John]
SubList stored in List: [Justin, Ajeet, John]

Note:
The subList method throws IndexOutOfBoundsException – if the specified indexes are out of the range of ArrayList (fromIndex < 0 || toIndex > size).
IllegalArgumentException – if the starting index is greater than the end point index (fromIndex > toIndex).

Java ArrayList lastIndexOf(Object 0bj) Method example

The method lastIndexOf(Object obj) returns the index of last occurrence of the specified element in the ArrayList. It returns -1 if the specified element does not exist in the list.

public int lastIndexOf(Object obj)
This would return the index of last Occurrence of element Obj in the ArrayList.

Example

In the below example we have an Integer ArrayList which has few duplicate elements. We are fetching the last index of few elements using lastIndexof method.

package beginnersbook.com;
import java.util.ArrayList;
public class LastIndexOfExample {
  public static void main(String args[]) {
      //ArrayList of Integer Type
      ArrayList<Integer> al = new ArrayList<Integer>();
      al.add(1);
      al.add(88);
      al.add(9);
      al.add(17);
      al.add(17);
      al.add(9);
      al.add(17);
      al.add(91);
      al.add(27);
      al.add(1);
      al.add(17);

      System.out.println("Last occurrence of element 1: "+al.lastIndexOf(1));
      System.out.println("Last occurrence of element 9: "+al.lastIndexOf(9));
      System.out.println("Last occurrence of element 17: "+al.lastIndexOf(17));
      System.out.println("Last occurrence of element 91: "+al.lastIndexOf(91));
      System.out.println("Last occurrence of element 88: "+al.lastIndexOf(88)); 
   }
}

Output:

Last occurrence of element 1: 9
Last occurrence of element 9: 5
Last occurrence of element 17: 10
Last occurrence of element 91: 7
Last occurrence of element 88: 1

Java ArrayList get() Method example

ArrayList get(int index) method is used for fetching an element from the list. We need to specify the index while calling get method and it returns the value present at the specified index.

public Element get(int index)

This method throws IndexOutOfBoundsException if the index is less than zero or greater than the size of the list (index<0 OR index>= size of the list).

Example

In below example we are getting few elements of an arraylist by using get method.

package beginnersbook.com;
import java.util.ArrayList;
public class GetMethodExample {
   public static void main(String[] args) {
       ArrayList<String> al = new ArrayList<String>();
       al.add("pen");
       al.add("pencil");
       al.add("ink");
       al.add("notebook");
       al.add("book");
       al.add("books");
       al.add("paper");
       al.add("white board");

       System.out.println("First element of the ArrayList: "+al.get(0));
       System.out.println("Third element of the ArrayList: "+al.get(2));
       System.out.println("Sixth element of the ArrayList: "+al.get(5));
       System.out.println("Fourth element of the ArrayList: "+al.get(3));
   }
}

Output:

First element of the ArrayList: pen
Third element of the ArrayList: ink
Sixth element of the ArrayList: books
Fourth element of the ArrayList: notebook

Java ArrayList indexOf() Method example

Java.util.ArrayList class method indexOf(Object o) is used to find out the index of a particular element in a list.

Method indexOf() Signature

public int indexOf(Object o)
This method returns -1 if the specified element is not present in the list.

ArrayList indexOf() Method example

In the following example we have an arraylist of strings and we have added few elements to the arraylist. Here we are using the indexOf() method to find the index of few specified elements in the ArrayList.


import java.util.ArrayList;
public class IndexOfExample {
  public static void main(String[] args) {
      ArrayList<String> al = new ArrayList<String>();
      al.add("AB");
      al.add("CD");
      al.add("EF");
      al.add("GH");
      al.add("IJ");
      al.add("KL");
      al.add("MN");

      System.out.println("Index of 'AB': "+al.indexOf("AB"));
      System.out.println("Index of 'KL': "+al.indexOf("KL"));
      System.out.println("Index of 'AA': "+al.indexOf("AA"));
      System.out.println("Index of 'EF': "+al.indexOf("EF"));
  }
}
Output:
Index of 'AB': 0
Index of 'KL': 5
Index of 'AA': -1
Index of 'EF': 2
As you can see in the output that the index of element ‘AA’ is returned as -1 because this element does not exist in the ArrayList.

ArrayList indexOf() Method example if duplicate elements are present

In the following example, the element 90 is present twice in ArrayList, at the index 0 and index 3. When we used the indexOf() method to find the index of 90, we got the index of first occurrence of 90, this is because this method returns the index of first occurrence of the specified element. If you want to find out the last occurrence of the specified element use lastIndexOf() method instead.
import java.util.ArrayList;
public class JavaExample {
   public static void main(String[] args) {
      ArrayList<Integer> al = new ArrayList<Integer>();
      al.add(90);
      al.add(15);
      al.add(20);
      al.add(90);

      System.out.println("Index of 90: "+al.indexOf(90));
      System.out.println("Index of 20: "+al.indexOf(20));
      System.out.println("Index of 15: "+al.indexOf(15));
   }
}
Output:

Java ArrayList contains() Method example

ArrayList contains() method is used for checking the specified element existence in the given list.

public boolean contains(Object element)

It returns true if the specified element is found in the list else it gives false.

Example

In this example we have two array lists (ArrayList<String> and ArrayList<Integer>) and we are checking the existence of few elements in both the lists.

package beginnersbook.com;
import java.util.ArrayList;
public class ContainsExample {
   public static void main(String[] args) {

      ArrayList<String> al = new ArrayList<String>();
      al.add("pen");
      al.add("pencil");
      al.add("ink");
      al.add("notebook");

      System.out.println("ArrayList contains the string 'ink pen': "
                                           +al.contains("ink pen"));
      System.out.println("ArrayList contains the string 'pen': "
                                             +al.contains("pen"));
      System.out.println("ArrayList contains the string 'pencil': "
                                          +al.contains("pencil"));
      System.out.println("ArrayList contains the string 'book': "
                                           +al.contains("book"));

      ArrayList<Integer> al2 = new ArrayList<Integer>();
      al2.add(1);
      al2.add(99);
      al2.add(56);
      al2.add(13);
      al2.add(44);
      al2.add(6);

      System.out.println("'1' is present in arraylist: "+al2.contains(1));
      System.out.println("'55' is present in arraylist: "+al2.contains(55));
      System.out.println("'44' is there in arraylist: "+al2.contains(44));
      System.out.println("'7' is there in arraylist: "+al2.contains(7));
   }
}

Output:

ArrayList contains the string 'ink pen': false
ArrayList contains the string 'pen': true
ArrayList contains the string 'pencil': true
ArrayList contains the string 'book': false
'1' is present in arraylist: true
'55' is present in arraylist: false
'44' is there in arraylist: true
'7' is there in arraylist: false