Searching in Java Array sounds familiar? should be, because its one of frequently used operations
in Java programming. Array is an index based data structure which is used to
store elements but unlike Collection classes like ArrayList or HashSet which has contains() method, array
in Java doesn't have any method to check whether an element is inside array or
not. Java programming language provides several ways to search
any element in Java array. In this Java tutorial we will see 4 examples of
searching Array in Java for an element or object. Every example is different than other and some
of them are faster and others are slow but take less memory. These technique
also valid for different types of array e.g. primitive and object array. I
always suggest to prefer
List over Array until you need every bit of performance from your Java
application, it not only convenient to work but also more extensible.
4 ways to search array in Java
Here are my 4 ways to search Java Array with examples
1) Searching Array by converting Array to ArrayList in Java
ArrayList in Java has a convenient method called contains() whichreturns true if object passed to it are inside ArrayList. by converting
an array into ArrayList in Java we can easily use this option for searching
any element in Java array.
2) Search Java array by converting Array to HashSet
Just like we can leverage ArrayList's contains
method we can also use HashSet contains() method which has O(1) response
time for search. So if you need constant search time to find an element in array,
consider converting your Array into HashSet in Java. see the code section for complete
example of searching elements in Java array using HashSet's contains()
method.
3) Searching Java Array using Arrays.binarySearch()
Binary Search is another faster way of searching elements in Java array but it requires array to be sorted
while earlier examples of finding elements on Array can be used with both sorted
and unsorted array. java.util.Arrays class provides both sort() and binarySearch() for first
sorting an array and than performing binary search on it. Arrays.binarySearch() method returns
>=0 if it finds elements in Array. see code section for full code example of
binarySearch in Java array.
4) Finding element in Java array using foreach loop
This is plain, old, brute force way of searching elements on array in Java
or any other programming language like C or C++. You iterate
through array comparing each elements to input and returning true once you
have matched. this is a completely linear operation and if your array is large
and input is at rear end it can take long time to search array. O(n) operations
are also not preferred.
One more way of searching an element in array is by using Apache commons ArrayUtils class. ArrayUtils class provide several overloaded method which accept array and item to be found e.g. int array, long array or Object array and returns true or false if Array contains that element. This requires just one line of code but you need to include Apache commons library in your classpath. See How to find index of element in Java array for complete code example in Java.
Code Example of Searching Java array to find elements
here is complete code examples of all 4 ways of searching java arrays.
you can use any way as per your need but HashSet() is best in
terms of speed and consider using that.
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
public class
SearchTest {
public static void
main(String args[])
{
//searching element
on unsorted Java array
//searching java
array using ArrayList
List<Integer> array = Arrays.asList(1, 3, 5, 2, 4);
if (array.contains(3)) {
System.out.println("Element found
inside Java array using" +
"ArrayList
contains() method");
};
Set<Integer> arraySet = new
HashSet<Integer>(array);
if (arraySet.contains(3)) {
System.out.println("Element found on
Java array using" +
"HashSet contains method");
};
//searching element
on sorted Java array
//unsorted String
array
String[] cities = new
String[]{"Washington",
"London", "Paris",
"NewYork"};
//sorting array in
java
Arrays.sort(cities);
//searching on
sorted array in java using Arrays binarySearch() method
if(Arrays.binarySearch(cities, "Paris") >=0 ){
System.out.println("Element found on
sorted String Java" +
"array
using binary search");
}
//plain old for loop
for searching elements in Java array
String input = "London";
for(String city: cities){
if(city.equals(input)){
System.out.println("Found elements in
Java array using for loop");
}
}
}
}
Output
Element found inside Java
array using ArrayList contains() method
Element found on Java
array using HashSet contains method
Element found on sorted
String Java array using binary search
Found elements in Java
array using for loop
That’s all on How to search an element inside Array in Java. You can use
any of the above method to search your Java array for any object. Remember that Collection classes like HashSet and ArrayList use equals()
method to determine if two objects are equal or not. So if your testing for
custom objects make sure you override equals and hashCode method and follow equals
and hashCode contract in Java.
Other Java Collection tutorials and examples from Javarevisited
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