Arrays In Java

Detailed explanation of Java arrays: one-dimensional arrays and multi-dimensional arrays

Hello everyone?! Today we will talk about arrays in Java. Arrays are used to store multiple values ​​in one variable instead of declaring separate variables for each value. There are two types of arrays in Java: one-dimensional arrays and multi-dimensional arrays.

An array is an object, so it stores a reference to the data it stores. Arrays can store two types of data:

• A collection of basic data types
• Collection of objects

Arrays of primitive types store the collection of values ​​that make up the primitive value itself. Object arrays store collections of values, which are actually heap memory addresses or pointers.

Members of an array are defined in contiguous memory locations, thus improving access speed.

The following code creates a basic data array:

public class Main {
    public static void main(String[] args) {

        // 初始化数组
        int[] arr = {1, 2, 3, 4, 5};

        // 数组大小
        int n = arr.length;

        // 遍历数组
        for (int i = 0; i < n; ++i)
            System.out.print(arr[i] + " ");
    }
}

Examples of int basic data type array and String object array

A one-dimensional array is an object that references a collection of scalar values. Two-dimensional arrays are called multidimensional arrays. A two-dimensional array refers to a collection of objects, where each object is a one-dimensional array.

One-dimensional array in Java

• A one-dimensional array in Java is a linear array that allows the storage of multiple values ​​of the same data type.
• It is a data collection that stores elements of the same type in sequentially allocated space in memory.
• One-dimensional arrays can be used to store simple and complex data types, anything from strings, integers, and Boolean values ​​to classes customized to user needs.

Multidimensional arrays in Java

• A multidimensional array in Java is an array of arrays, i.e. it is an array object with multiple dimensions.
• Multidimensional arrays are very useful when working with large amounts of data because of their ability to store and access data from a single variable, but with multiple hierarchies.
• This multi-dimensional array can be expanded to a certain number of dimensions, such as two-dimensional, three-dimensional, etc.

The number of bracket pairs indicates the depth of array nesting. Java has no theoretical limit on the level of array nesting. Square brackets can follow the array type or its name.

The array type can be any of the following:

• Basic data types
• Interface
• Abstract class
• Concrete class

Combined array declaration, allocation and initialization

int intArray[] = {0, 1};
String[] strArray = {"Summer", "Winter"};
int multiArray[][] = {{0, 1}, {3, 4, 5}};

Above code:

• Do not use keyword new to initialize array
• Do not specify the size of the array
• Use one pair of brackets to define the value of a one-dimensional array, and use multiple pairs of brackets to define a multi-dimensional array

All previous array declaration, allocation and initialization steps can also be combined in the following way:

public class Main {
    public static void main(String[] args) {

        // 初始化数组
        int[] arr = {1, 2, 3, 4, 5};

        // 数组大小
        int n = arr.length;

        // 遍历数组
        for (int i = 0; i < n; ++i)
            System.out.print(arr[i] + " ");
    }
}

Unlike the first method, the previous code uses the keyword new to initialize the array. If you try to specify the size of the array using the previous method, the code will not compile. Here are some examples:

int intArray[] = {0, 1};
String[] strArray = {"Summer", "Winter"};
int multiArray[][] = {{0, 1}, {3, 4, 5}};

Key points

1. Multidimensional arrays in Java are implemented as arrays of arrays, not true matrices.
2. The array length may be different for each row (jagged array).
3. You can access elements using indexes, such as arrayName[rowIndex][columnIndex].
The
4. length attribute provides the number of rows or the size of a specific row.

I will introduce it in detail in the next article tomorrow.

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