Java subarray without copy

Get a subarray of an array between specific index in Java

This post will discuss several methods to get a subarray of a non-primitive array between specified indices in Java.

1. Using Arrays.copyOfRange() method

The standard way to get a subarray of an array is to use the Arrays.copyOfRange() , which returns a subarray containing the specified range from the original array, as shown below:

Output:

[B, C, D, E]

2. Using Java 8

We can use the Java Stream, introduced in Java SE 8, to get a subarray from an array. The idea is to get a stream of elements between the specified range and then call the toArray() method to accumulate the stream elements into a new array.

Output:

[B, C, D, E]

3. Using System.arraycopy() method

System.arraycopy() method can also be used to get a copy from the specified position in the source array to the specified position of the destination array.

Output:

[B, C, D, E]

4. Converting to List

Here, the idea is to convert the array into a list and use the subList() method to get elements between the desired range. Then, we use the toArray(T[]) method to copy the list into a newly allocated array.

Please note that this method doesn’t actually copy the array. Both the resultant list and the sublist are backed by the original array and just references the array.

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Obtaining a Subarray in Java: A Guide

The function copies a specific range of an array into a newly created slice array and returns the slice array. The specified range is taken from the original array. For example, if you want to create a smaller array, you can adjust the start and end points of the loop and the indices accessed within the loop. Solution 3 involves creating a new array and initializing the subarray by looping through the relevant indices of the original array.

How to get a sub array of array in Java, without copying data?

Arrays.asList(array).subList(x, y). 

Instead of providing an array, this approach yields a List that offers greater versatility.

It is possible that the subset of an array would suffice as a parameter for several Java classes. For instance, the method Writer.write(char cbuf[], int off, int len) accepts such a subset.

In Java, it is impossible to wrap data without copying it and obtain an actual array. It is not feasible to generate a new array over current memory. Essentially, you have two alternatives.

• Employ techniques that can handle arrays with a variety of values, as previously suggested.
• Below, we will discuss a wrapper that provides an abstraction similar to an array and is appropriate for various applications.

Utilizing the class hierarchy of java.nio.Buffer is recommended, particularly java.nio.ByteBuffer , as it provides buffer abstraction for an entire array or sub-ranges, which is commonly sought after. Additionally, it presents various advantageous features such as the ability to perform ‘zero copy’ flip and represent flexible byte areas.

An instance of wrapping is demonstrated by utilizing java.nio.ByteBuffer . This should be almost identical to what you require, particularly for certain operations.

byte [] a1 = ; ByteBuffer buf = ByteBuffer.wrap(a1,1,2); 

Perform any operation on buf using ByteBuffer .

Please be advised that utilizing buf.array() will yield the unaltered a1 array from the backend, containing all of its original elements.

Get only part of an Array in Java? [duplicate], The length of an array in Java is immutable. So, you need to copy the desired part into a new array. Use copyOfRange method from java.util.

Print all subarrays of a given array

To master practice data structure and algorithm programs, you can explore over 100 data structure and algorithm programs.

This article will demonstrate the process of displaying all subarrays that belong to a specified array.

Problem

Generate subarrays for a given array and print them out. As an illustration, consider the following:

Solution

Given an array with n elements, the total number of subarrays can be calculated using the formula (n*n+1)/2. An algorithm to compute this can be easily implemented.

• We will employ a triplet of loops to display subarrays.
• The start index will be obtained through the utilization of the outer loop.
• The initial inner loop will retrieve the ending index.
• The second loop will be employed to display the elements between the start and end indices.

A straightforward code is available to display every subarray of a provided array.

How to count the number of subarrays within a bigger array using, Note: I left an intentional flaw with this code. You don’t actually want to use the Arrays.copyOf() in this use-case because it could get very

Array Slicing in Java

Array slicing is a method in Java for obtaining a subarray from an existing array. Consider an array a[], which contains eight elements that are indexed from a[0] to a[7].

Our objective is to retrieve a portion of the array, specifically the index range between a[3] and a[6]. The starting index is a[3], while the end index is a[6]. As a result, we obtain a sliced array.

This segment will cover the process of locating a section of an array in Java.

To obtain a segment of an array, there are three methods available:

Let’s discuss each method in detail.

By Copying Elements

The process of obtaining a section of an array is done through a built-in technique. Initially, the beginning and ending points of the array are determined. Then, a vacant array (sliced array ) with dimensions equal to (endIndex — startIndex) is produced. The elements of the original array are then copied starting from the startIndex and are placed in the sliced array. Finally, the sliced array is output.

We can apply the previously mentioned technique in a Java code to obtain a subset of the provided array. The program will utilize an array of basic data types.

An example Java file that demonstrates slicing an array is called SliceArrayExample1.java.

import java.util.Arrays; public class SliceArrayExample1 < //creating a functiion to the slice of an array public static int[] getSlice(int[] array, int startIndex, int endIndex) < // Get the slice of the Array int[] slicedArray = new int[endIndex - startIndex]; //copying array elements from the original array to the newly created sliced array for (int i = 0; i < slicedArray.length; i++) < slicedArray[i] = array[startIndex + i]; >//returns the slice of an array return slicedArray; > //main() method public static void main(String args[]) < //array from which we will find the slice int[] array = ; //start index and end index denotes the part of the original array to be slice int startIndex = 3, endIndex = 8; //Get the slice of the array int[] slicedArray = getSlice(array, startIndex, endIndex + 1); //prints the slice array System.out.println("Slice of Array: "+Arrays.toString(slicedArray)); > >

Slice of Array: [22, 45, 90, 67, 91, 0]

By Using the copyOfRange() Method

The Java Arrays class includes the copyOfRange() method, which generates a new array (known as a slice array) containing the designated range from the original array and returns it. Creating a slice array requires O(n) time and O(n) space to store elements, where n represents the number of elements in the resulting array.

public static int[] copyOfRange(int[] original, int from, int to)

The three parameters are parsed by the method.

• The objective is to locate the slice of an array.
• The starting index must be within the range of 0 to the length of the given array.
• The final index has been reached.

It throws the following exceptions:

• An ArrayIndexOutOfBoundsException occurs when the value of «from» is either negative or exceeds the length of the array specified.
• An IllegalArgumentException will occur if the value of the «from» parameter is larger than the «to» parameter.
• In case the array provided is null, a NullPointerException will occur.

The Java file example named «SliceArrayExample2» is being referred to.

import java.util.Arrays; public class SliceArrayExample2 < //function to get slice of a primitive array in Java public static int[] slice(int[] array, int startIndex, int endIndex) < // Get the slice of the Array int[] slicedArray = Arrays.copyOfRange(array, startIndex, endIndex); // return the slice return slicedArray; >public static void main(String args[]) < //get the array, startIndex and endIndex int[] array = ; int startIndex = 2, endIndex = 6; //get the slice of the array int[] sliceArray = slice(array, startIndex, endIndex + 1); //prints the slice of an array System.out.println("Slice of Array: "+Arrays.toString(sliceArray)); > >

Slice of Array: [56, 90, 111, 901, 251]

By Using Java 8 Stream

The slice of an array can be obtained through the Java 8 Stream by following the subsequent steps.

• Begin by locating the array’s startIndex and endIndex.
• Utilize the range() method to transform the elements that fall within a specific range into a Primitive Stream.
• Employ the map() function to extract specific elements from an array.
• Use the toArray() method to transform the mapped array into a regular array.
• Produce the portion that has been cut.

Example3.java, which demonstrates how to slice an array, is presented in SliceArrayExample3.

import java.util.Arrays; import java.util.stream.IntStream; public class SliceArrayExample3 < //user defined function that finds the sslice of an specified array public static int[] findSlice(int[] array, int startIndex, int endIndex) < //getting the slice of an array and storing it in array slcarray[] //the range() method converts the elements into stream //getting the elments of the int stream using lambda expression //converting the mapped elements into sliced array using the toArray() method int[] slcarray = IntStream.range(startIndex, endIndex).map(i ->array[i]).toArray(); //returns the slice of array return slcarray; > //main() method public static void main(String args[]) < //Get the array, startIndex and endIndex int[] array = ; int startIndex = 5, endIndex = 10; //Get the slice of the array int[] slcarray = findSlice(array, startIndex, endIndex + 1); //Print the slice of the array System.out.println("Slice of array for the specified range is: "+Arrays.toString(slcarray)); > >

Slice of array for the specified range is: [100, 345, 897, 67, 123, 0]

Find subarray with given sum | Set 1 (Non-negative Numbers), The idea is to consider all subarrays one by one and check the sum of every subarray. Following program implements the given idea. Run two loops

How to get 2D subarray from 2D array in JAVA?

 int[][] temp = < < 1, 2, 3, 4 >, < 5, 6, 7, 8 >, < 9, 10, 11, 12 >>; int[][] a = new int[temp.length][]; for (int i = 0; i < temp.length; i++) < a[i] = Arrays.copyOfRange(temp[i], 1, 3); >System.out.println(Arrays.deepToString(a)); 

In response to your comment, if our aim is to solely retrieve the elements of [[6, 7], [10, 11]], we can do so.

 int[][] a = new int[2][]; for (int i = 1, j = 0; i

For instance, by not utilizing the Arrays class.

int[][] temp = < < 1, 2, 3, 4 >, < 5, 6, 7, 8 >, < 9, 10, 11, 12 >>; int[][] subArray = new int[temp.length][]; for (int i = 0; i

After obtaining the subArray, you would have the ability to retrieve any desired component. For instance, accessing [[6, 7], [10, 11]] would be feasible.

To cater to the revised query,

To generate a reduced array, you can experiment with altering the loop’s start and end points, as well as the indices accessed inside the loop. For instance, the following code will yield the desired array.

int[][] subArray = new int[2][]; for (int i = 1; i

One option is to create a new array and use a loop to initialize the subarray with the corresponding indices from the original array.

How can use stream API for divide the array into sub array, You could either use Collectors.partitioningBy : Map> map = list.stream().collect(Collectors.partitioningBy(element ->

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