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About Armando Flores

Armando Flores
Armando graduated from from Electronics Engineer in the The Public University Of Puebla (BUAP). He also has a Masters degree in Computer Sciences from CINVESTAV. He has been using the Java language for Web Development for over a decade. He has been involved in a large number of projects focused on "ad-hoc" Web Application based on Java EE and Spring Framework.

Java Array – java.util.Arrays Example

In this example, we will show the range of functionality provided by the Java Array class java.util.Arrays. The Arrays class of the java.util package contains several static methods that you can use to compare, sort, and search in arrays. In addition, you can use this class to assign a value to one or more elements of an array. This class is a member of the Java Collections Framework.

An array of integers (int[]) will be used as our base array in the following example to illustrate most of the methods provided by the java.util.Arrays class. But before dive into the practical examples for Arrays, let us understand the different types of arrays available in the Java programming language.

  • One-Dimensional Arrays: It is an array type that consists of the array type and name. The array type will determine the type of array and the elements will determine the type of element inside the array. Let us understand the declaration of One-D arrays with an example.
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    int[] arr1  // A one-dimensional array of integer elements.
    String[] arr2   // A one-dimensional array of string elements.
    float[] arr3    // A one-dimensional array of floating-point elements.
     
    Object[] arr4   // A one-dimensional array of object elements. This array can either consist of mixture of primitive type elements or secondary elements.
  • Multi-Dimensional Arrays: It is an array of arrays where each element holds a reference of another array. These types of arrays are also called Jagged Arrays and are defined in the following manner. Let us understand the declaration of Two-D arrays with an example.
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    int[][] arry1 = new int[10][20];    //a 2D array or matrix
    int[][][] arr2 = new int[10][20][10];   //a 3D array

    Please note, these days the IT industry has obsolete the use of multi-dimensional arrays due to the extensive use of collections.

  • Array Literals: These are used in a situation where the array size and variables are known. Let us understand the declaration of Array Literals with an example.
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    int[] intArray = new int[]{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };   // Declaring array literal

    In this, the array length is automatically determined by the number of elements.

1. Example of Java Arrays methods

Now let us start with an example to understand the basic declaration and different methods in Arrays. But before digging deep let us look at different methods we will be using in this example.

1.1 Arrays.toString() method

This method returns the String representation of the array enclosed in the square brackets ([]). Adjacent elements are separated by the comma character (i.e. a comma followed by a space). Let us understand this with a simple example.

Snippet

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Integer[] integerArray = { 2, 4, 3, 7, 21, 9, 98, 76, 74 };
System.out.printf("integerArray elements: %s\n", Arrays.toString(integerArray));

1.2 Arrays.asList() method

This method returns a list backed by a given array. In other words, both the list and array refer to the same location. Let us understand this with a simple example.

Snippet

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List integerList = Arrays.asList(integerArray);     // Returns a fixed-size list backed by the specified array.

1.3 Arrays.sort() method

This method sorts the specified array into ascending numerical order. Let us understand this with a simple example.

Snippet

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Arrays.sort(baseArray);

1.4 Arrays.binarySearch() method

This method returns an integer value for the index of the specified key in the specified array. Return a negative number if the key is not found and for this method to work properly, the array must be sorted. Let us understand this with a simple example.

Snippet

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int idx = Arrays.binarySearch(baseArray, 21);       // Searches the specified array of ints for the specified value using the binary search algorithm.

1.5 Arrays.copyOf() method

This method copies the specified array, truncates or pads with zeros (if necessary) so the copy has the specified length. Let us understand this with a simple example.

Snippet

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int[] copyOfArray = Arrays.copyOf(baseArray, 11);       // Copies the specified array, truncating or padding with zeros (if necessary) so the copy has the specified length.

1.6 Arrays.copyOfRange() method

This method copies the specified range of the specified array into a new array. The initial index of the range (from) must lie between zero and original.length, inclusive. Let us understand this with a simple example.

Snippet

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int[] copyOfRangeArray = Arrays.copyOfRange(baseArray, 5, 8);       // Copies the specified range of the specified array into a new array.

1.7 Arrays.fill() method

This method fills all elements of the specified array with the specified value. Let us understand this with a simple example.

Snippet

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int[] fillArray = new int[5];       // Assigns the specified int value to each element of the specified array of ints.
System.out.printf("fillArray (before): %s\n", Arrays.toString(fillArray));
Arrays.fill(fillArray, 1);
System.out.printf("fillArray (after): %s", Arrays.toString(fillArray));

1.8 Complete Example

Let us consider the below example where we will illustrate all the methods explained above.

JavaUtilArraysExample.java

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package com.javacodegeeks.examples;
 
import java.util.Arrays;
import java.util.List;
 
public class JavaUtilArraysExample {
 
    public static void main(String[] args) {
 
        Integer[] integerArray = { 2, 4, 3, 7, 21, 9, 98, 76, 74 };     // Base array for the example. It contains 9 elements.
        System.out.printf("integerArray size: %d\n", integerArray.length);
        System.out.printf("integerArray elements: %s\n", Arrays.toString(integerArray));
 
        List<Integer> integerList = Arrays.asList(integerArray);      // Returns a fixed-size list backed by the specified array.
        System.out.printf("integerList size: %d\n", integerList.size());
        System.out.printf("integerList elements: ");
        for (Integer i : integerList) {
            System.out.printf("%d ", i);
        }
        System.out.printf("\n\n");
 
        int[] baseArray = { 2, 4, 3, 7, 21, 9, 98, 76, 74 };
        System.out.printf("Unsorted baseArray: %s\n", Arrays.toString(baseArray));
 
        Arrays.sort(baseArray);
        System.out.printf("Sorted baseArray: %s\n", Arrays.toString(baseArray));
 
        int idx = Arrays.binarySearch(baseArray, 21);       // Searches the specified array of ints for the specified value using the binary search algorithm.
        System.out.printf("Value \"21\" found at index: %d\n\n", idx);
 
        System.out.printf("baseArray size: %d\n", baseArray.length);
        System.out.printf("baseArray elements: %s\n", Arrays.toString(baseArray));
 
        int[] copyOfArray = Arrays.copyOf(baseArray, 11);       // Copies the specified array, truncating or padding with zeros (if necessary) so the copy has the specified length.
        System.out.printf("copyOfArray size: %d\n", copyOfArray.length);
        System.out.printf("copyOfArray elements: %s\n\n", Arrays.toString(copyOfArray));
 
        System.out.printf("baseArray: %s\n", Arrays.toString(baseArray));      
        int[] copyOfRangeArray = Arrays.copyOfRange(baseArray, 5, 8);       // Copies the specified range of the specified array into a new array.
        System.out.printf("copyOfRangeArray: %s\n\n", Arrays.toString(copyOfRangeArray));
 
        int[] fillArray = new int[5];       // Assigns the specified int value to each element of the specified array of ints.
        System.out.printf("fillArray (before): %s\n", Arrays.toString(fillArray));
        Arrays.fill(fillArray, 1);
        System.out.printf("fillArray (after): %s", Arrays.toString(fillArray));
    }
}

If everything goes well, we will get the following results in the console.

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integerArray size: 9
integerArray elements: [2, 4, 3, 7, 21, 9, 98, 76, 74]
integerList size: 9
integerList elements: 2 4 3 7 21 9 98 76 74
Unsorted baseArray: [2, 4, 3, 7, 21, 9, 98, 76, 74]
Sorted baseArray: [2, 3, 4, 7, 9, 21, 74, 76, 98]
Value "21" found at index: 5
baseArray size: 9
baseArray elements: [2, 3, 4, 7, 9, 21, 74, 76, 98]
copyOfArray size: 11
copyOfArray elements: [2, 3, 4, 7, 9, 21, 74, 76, 98, 0, 0]
baseArray: [2, 3, 4, 7, 9, 21, 74, 76, 98]
copyOfRangeArray: [21, 74, 76]
fillArray (before): [0, 0, 0, 0, 0]
fillArray (after): [1, 1, 1, 1, 1]

2. Some more methods of the Arrays class

Java Arrays add some interesting method arguments to the existing sort() and fill() method i.e.

  • Arrays.sort(int[] a, int fromIndex, int endIndex): Sorts the specified range of the array into ascending order. The range to be sorted extends from the index fromIndex, inclusive, to the index toIndex, exclusive. If fromIndex == toIndex, the range to be sorted is empty
  • Arrays.fill(int[] a, int fromIndex, int endIndex): Fills elements of the specified array with the specified value from the fromIndex element, but not including the toIndex element

Let us understand these modifications with an example.

JavaUtilArraysMoreMethodsExample.java

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package com.javacodegeeks.examples;
import java.util.Arrays;
public class JavaUtilArraysMoreMethodsExample {
    public static void main(String[] args) {
        // Base array for the example. It contains 9 elements.
        int[] baseArray = { 2, 4, 3, 7, 21, 9, 98, 76, 74 };
        
        // Sorts the specified range of the array into ascending order.
        System.out.printf("Unsorted baseArray: %s\n", Arrays.toString(baseArray));
        
        Arrays.sort(baseArray, 1, 6);
        
        System.out.printf("Sorted baseArray: %s\n\n", Arrays.toString(baseArray));
        
        // Assigns the specified int value to each element of the
        // specified range of the specified array of ints.
        int[] fillArray = new int[10];     
        
        System.out.printf("fillArray (before): %s\n", Arrays.toString(fillArray));     
        
        Arrays.fill(fillArray, 1, 7, 3);
        
        System.out.printf("fillArray (after): %s", Arrays.toString(fillArray));
    }
}

If everything goes well, we will get the following results in the console.

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Unsorted baseArray: [2, 4, 3, 7, 21, 9, 98, 76, 74]
Sorted baseArray: [2, 3, 4, 7, 9, 21, 98, 76, 74]
fillArray (before): [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
fillArray (after): [0, 3, 3, 3, 3, 3, 3, 0, 0, 0]

That is all for this tutorial and I hope the article served you whatever you were looking for. Happy Learning and do not forget to share!

3. Download the Source Code

Download
You can download the source code of this example from here: Java Array – java.util.Arrays Example

Java Array – java.util.Arrays Example was last updated on Aug. 13th, 2019

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